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Engineering Structures
Journal Prestige (SJR): 1.69
Citation Impact (citeScore): 3
Number of Followers: 15  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0141-0296
Published by Elsevier Homepage  [3168 journals]
  • Temperature-stress-time methodology for flat-patterning ETFE cushions in
           use for large-span building structures
    • Abstract: Publication date: Available online 30 November 2019Source: Engineering StructuresAuthor(s): Jianhui Hu, Wujun Chen, Yipo Li, Yegao Qu, Bing Zhao, Deqing YangAbstractEthylene tetrafluoroethylene (ETFE) cushion structures with excellent building aesthetics and reasonable structural behavior can be utilized as roofs and facades of large-span building structures. The form and force of such structures interact due to structural flexibility and complexity. The determination of a suitable form needs form-finding and cutting pattern for conventional ETFE cushions, which incorporates complex theoretical analysis and fabrications. To obtain a structural form without complex cutting pattern, a flat-patterning ETFE cushion is proposed based on creep properties of polymer materials. This methodology facilitates to achieve desired forms using creep models of ETFE foils. Moreover, time-temperature superposition of polymer materials is employed to improve this method. Therefore, this paper focuses on a modified creep model of ETFE foils and utilizes it to assess form and force of flat-patterning ETFE cushion structures.The Bailey-Norton model with Modified Time Hardening effect results in a creep model that describes creep strains at high temperature. To integrate this model into software, a multi-linear model is used where parameters are determined with experimental results. The related numerical simulations demonstrate the suitability of reproducing creep strains. For structural analysis, two typical cushions with inverse temperatures and pressures are simulated with multi-linear models. It is found that the maximum stress and strain exist near middle area of long edges and propagate towards cushion center. The final deformations of two cushions are 21.2 mm and 19.4 mm; the ratios of heights to edge length are larger than the engineering ratio of 1/8, resulting in a suitable structural form. A further ratio of stress to yield stress suggests the easy operation to achieve desired forms for small pressure at high temperature than large pressure at low temperature. In general, the proposed method to reveal form and structural behavior is useful for promoting utilizations of flat-patterning ETFE cushions.
       
  • Multi-hazard fragility analysis for a wind turbine support structure: An
           application to the Southwest of Mexico
    • Abstract: Publication date: Available online 30 November 2019Source: Engineering StructuresAuthor(s): J.O. Martín del Campo, A. Pozos-EstradaAbstractThe scenario of growing demand for construction of wind turbine structures in Mexico poses the need of analyzing the hazards that affect this kind of structures in that country. Current Mexican standards include wind turbine support structures in their earthquake design chapter, but no information is included regarding the wind design. This work focuses on the analysis of an onshore 5 MW wind turbine structure, similar to those currently installed in Mexico, under the simultaneous action of wind and earthquake for different intensities. The analyses performed consider the rotor in both: parked and in operation conditions. Wind speed records are obtained from simulations based on an Auto Regressive and Moving Average model and the Veers’ method, while the ground motion records are simulated to be consistent with design spectra for a zone in the Southwest of Mexico, near the coast of the Pacific Ocean, which happens to be the region with the greatest installed wind capacity in Mexico and also a region of strong seismic hazard. The numerical results obtained are employed in a multi-hazard fragility analysis, which shows that the critical action for the structure depends on the operational state of the turbine.
       
  • Experimental and numerical study of honeycomb structural fuses
    • Abstract: Publication date: Available online 30 November 2019Source: Engineering StructuresAuthor(s): T.Y. Yang, Tianyi Li, Lisa Tobber, Xiao PanAbstractThis paper presents a novel metallic damper, named Honeycomb Structural Fuse (HSF), for seismic applications. The HSF utilizes commonly available welded wide flange sections with honeycomb-shape perforations on web. The HSF is designed to dissipate earthquake energy through plastic deformation of the web in shear, while the flanges remain elastic. The HSF can be fabricated into different shapes to fit different structural demands. To investigate the seismic performance of the HSF, a total of nine specimens with different honeycomb cell wall aspect ratios (cell wall thickness to cell wall center length) and honeycomb cell combinations (number of rows and columns) were manufactured and tested under displacement-based static cyclic loading. The influence of the different geometry parameters on the initial stiffness, yield force, yield drift, force-drift relationship, buckling, and failure modes are summarized in this paper. Finally, a robust finite element model was built to simulate the hysteresis behavior of the HSF. The effectiveness of the proposed model was validated using experimental results. The study shows that the newly proposed HSF has stable energy dissipation, which can be used as an efficient metallic damper for seismic applications.
       
  • Experimental investigation on axial compression behavior of steel
           reinforced concrete columns with welded stirrups
    • Abstract: Publication date: Available online 30 November 2019Source: Engineering StructuresAuthor(s): Lele Sun, Qijie Ma, Fei Han, Zexin Liu, Jinglong Li, Peijun Wang, Hui Zhao, Jian SunAbstractTest results on Steel Reinforced Concrete Column with Welded Stirrups (SRCC-WS) were presented and a simplified design method was proposed. The SRCC-WS had no longitudinal steel bars to reduce the labor forces and avoid the difficulty in connecting longitudinal bars at construction site, and stirrups were welded directly to the steel reinforcement to ensure they worked together. Five SRCC-WSs were tested under axial compression; and two traditional Steel Reinforced Concrete Columns (SRCCs) were tested for comparison. Failure modes, load-displacement curves, and strain evolution curves measured from tests were presented. Test results showed that the ultimate axial compression strength and ductility of a SRCC-WS was a little higher than that of a SRCC having the same overall steel ratio. A simplified design method for calculating the effective lateral confined pressure on the core concrete provided by the combined action of welded stirrups and steel reinforcement flanges was proposed. The calculated yield compression strength of a SRCC-WS based on the proposed concrete model agreed better with the experimental value than that calculated by the method in Eurocode 4.
       
  • Theoretical method of determining pier settlement limit value for
           China’s high-speed railway bridges considering complete factors
    • Abstract: Publication date: Available online 30 November 2019Source: Engineering StructuresAuthor(s): Zhaowei Chen, Wanming ZhaiAbstractReasonable pier settlement is an extremely important limit value in the design of high-speed railway bridges, which directly affects the service performance of bridges and the running safety of trains. Comprehensively considering complete factors affecting the determination of pier settlement limit value (PSLV), this paper presents a method to investigate PSLV for simply supported girder bridges in China’s high-speed railways. First of all, an investigation on PSLV written in China’s current codes is conducted to explain the necessity of this present work. Then based on the train-track-bridge dynamic interaction theory, the methodology for determining PSLV for China’s high-speed railway bridges is proposed, in which the complete factors affecting the determination of PSLV are emphatically discussed and summarized. Adopting the established model, the bridge deformations caused by different factors are calculated, and the PSLV for China’s high-speed railway bridges is then obtained according to the running safety and ride comfort of high-speed trains. Results show that important factors written in codes, including self-weight, prestress, creep, shrinkage, temperature and rail random irregularity, should be fully considered in determining PSLV due to these factors greatly affect bridge deformations and dynamic behaviors of running trains. According to the running safety and ride comfort of high-speed trains, the PSLV for simply supported girder bridges in China’s high-speed railways is suggested to 12.7 mm.
       
  • Acoustic emission monitoring of containment structures during
           post-tensioning
    • Abstract: Publication date: Available online 30 November 2019Source: Engineering StructuresAuthor(s): Arvin Ebrahimkhanlou, Jongkwon Choi, Trever D. Hrynyk, Salvatore Salamone, Oguzhan BayrakAbstractThis paper introduces a method based on acoustic emission (AE) to monitor the onset of delamination in post-tensioned concrete containment structures. The method is based on clustering AE occurring during post-tensioning and/or re-tensioning such structures. In particular, the investigation is focused on AE of a large-scale, curved concrete wall subject to monotonically increasing prestressing forces. This specimen is a representative of typical cylindrical concrete structures, such as water storage tanks, silos, bins, and nuclear containment structures. To analyze AE data, this paper uses both time-driven and hit-driven features extracted from AE. To this end, a novel approach is proposed to analyze and visualize hit-driven features. To detect and localize such defects, the proposed approach identifies an optimal number of clusters in AE data and interprets each cluster based on the physical mechanism that generates it. Such interpretations are compared with the state of stresses and modified Mohr–Coulomb failure criteria. The results show that the AE events are due to three categories of source mechanisms, micro shear cracking, micro tensile cracking, and macro delamination cracking. To validate the results, comparisons are made with through-thickness expansion measurements of the wall. The results demonstrate that the proposed approach can detect delamination defects and enable decision makers to take remedial and preventive actions.
       
  • Blast-induced damage and evaluation method of concrete gravity dam
           subjected to near-field underwater explosion
    • Abstract: Publication date: Available online 30 November 2019Source: Engineering StructuresAuthor(s): Xiao-hua Wang, She-rong Zhang, Chao Wang, Wei Cui, Ke-lei Cao, Xin FangAbstractBomb attacks from terrorists have become potential risks to important infrastructures, most of which were built without considering their vulnerability to such events. This paper focuses on the blast-induced damage to concrete gravity dams subjected to near-field underwater explosions. Different from direct damage mode analysis, a novel vibration-based damage evaluation method is proposed to illustrate the damage state of a dam after an explosion. To this end, a three-dimensional fluid-solid coupling numerical model in LS-DYNA is proposed for simulating the shock wave propagation and its interaction with dam structures, in which the explosive, air, and water are meshed by an arbitrary Lagrangian-Eulerian (ALE) formulation, while the dam and its foundation are meshed by the Lagrange formulation. Then, the structural responses and damage characteristics of the dam are investigated under various explosion scenarios considering changes in explosive charge, standoff distance and detonation depth. On this basis, the optimized vibration characteristics, including peak velocity summation (PVS) and mean frequency (MF), are adopted to evaluate the vulnerability of concrete gravity dams subjected to underwater explosions, which is better than the traditional damage evaluation method based solely on the peak particle velocity (PPV). The PVS-MF spectrum criterion proposed in this study is feasible to evaluate the damage state of concrete gravity dams after underwater explosions, and the results can be used in the blast-resistance design of similar hydraulic engineering.
       
  • Testing and numerical modelling of S960 ultra-high strength steel angle
           and channel section stub columns
    • Abstract: Publication date: Available online 29 November 2019Source: Engineering StructuresAuthor(s): Fangying Wang, Ou Zhao, Ben YoungAbstractA comprehensive experimental and numerical study of the cross-sectional compressive behaviour and resistances of press-braked S960 ultra-high strength steel (UHSS) angle and channel section stub columns is reported in this paper. The experimental study was carried out on four equal-leg angle sections and eight plain channel sections, and comprised material testing, initial local geometric imperfection measurements and 18 stub column tests. The experimental setups, procedures and key observations were fully presented. The experimental study was then supplemented by a finite element (FE) simulation programme, in which FE models were firstly developed to replicate the test structural responses and subsequently used to generate further numerical data over a wide variety of cross-section sizes. It is worth noting that the current international standards established in Europe, America and Australia/New Zealand only cover the design of structural members with material grades up to S700, and thus the examined S960 UHSS angle and channel section stub columns are out of the scope of the existing design standards. In this study, the experimentally and numerically acquired data was adopted to assess the applicability of the codified provisions and formulations to the design of S960 UHSS angle and channel section stub columns. The assessment results generally indicated that the current European code leads to overall consistent and accurate predictions of cross-section compression resistances, but with many overestimated predicted resistances for S960 UHSS channel section stub columns, while the American and Australian/New Zealand standards yield unduly scattered design cross-section compression resistances, with unsafe and overly conservative predicted resistances respectively for S960 UHSS channel section stub columns and slender angle section stub columns. Revised codified design rules were also proposed, and shown to yield safe, accurate and consistent design cross-section compression resistances for S960 UHSS angle and channel section stub columns.
       
  • Transient analysis of hybrid SMA-FRP reinforced concrete beams under
           sequential impacts
    • Abstract: Publication date: Available online 29 November 2019Source: Engineering StructuresAuthor(s): Erfan Shafei, Reza KianoushAbstractDamage growth and plasticity under impact loads is a major concern in steel reinforced concrete (RC) structures. Yielding of steel reinforcements results in delay in repair of RC members after impacts and shock loads. In an effort to mitigate the impact-induced damage, this paper investigates numerically a hybrid type of reinforcing rebar made of fiber reinforced polymer (FRP) with integrated super-elastic shape memory alloy (SMA) fibers. Hybrid SMA-FRP rebar has both ductility and super-elasticity features, which is used to improve the sequential impact response in current work. Primarily, the experimentally validated constitutive models are used to simulate the transient response of RC beams. Moreover, hybrid SMA-FRP reinforced beams with various rebar ratios are modeled and subjected to sequential drop weight impacts. The results of regular and hybrid SMA-FRP reinforced beams are compared based on the damage growth, energy balance of materials, maximum and residual displacement, acceleration, and reaction forces. Numerical results show enhanced performance of SMA-FRP rebar in terms of energy dissipation and damage mitigation. The accumulation of concrete damage and rebar yielding resulted in increasing residual displacement in regular beams. However, super-elasticity of SMA and high strength of FRP lead to remarkable displacement recovery in hybrid SMA-FRP RC beams.
       
  • Experimental investigation of the hysteretic performance of self-centering
           buckling-restrained braces with friction fuses
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Qin Xie, Zhen Zhou, Shao-Ping MengAbstractThe dual-tube self-centering buckling-restrained brace (SC-BRB) is a new bracing system with self-centering and energy dissipation capacity. The current dual-tube SC-BRB is limited by the elastic elongation of the tendons. When the lateral deformation of existing dual-tube SC-BRBs exceeds 2.6% of a typical building story height, the tendons will be fractured, and this fracture will lead to a sudden drop of the bearing capacity of the brace and loss of the self-centering capacity. In this paper, an SC-BRB with a friction fuse (SC-BRB-FS) is proposed by introducing a friction device at the end of the brace to increase the deformation capacity of the dual-tube SC-BRB. At the same time, two bracing specimens are built for a quasi-static test. Activation of the friction fuse can efficiently increase the deformation capacity of the brace. When the displacement reaches 36 mm (corresponding to a story drift of 4%), the tendons are still not damaged. The nonlinear dynamic time-history analysis of the structure shows that compared with the fracture of tendons, the use of a friction fuse not only restrains the soft-story effect and reduces the collapse probability of the structure but also reduces the residual deformation of the structure.
       
  • Initial motion analysis of traditional Chinese rocking timber frame
           subjected to horizontal ground motion: Theoretical and numerical
           investigations
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Jia Wan, Qingshan Yang, Jianwei Wei, Tieying LiAbstractThe traditional Chinese timber structure with columns directly placed on the foundation has the characteristics of the rocking structure. Determining initial modes of response under horizontal acceleration is essential to the analysis of subsequent response for rocking structures. This paper extends the initial mode criteria of the rigid free-standing column to the plane motion of the traditional Chinese timber frame to obtain the analytical distribution of the timber frame. A finite element model of the typical traditional Chinese timber frame was established and then a parameter analysis was performed; the simulation results were consistent with the analytical distribution. The results have identified four types of initial modes: rest, slide, pure-rock, and slide-rock. For the traditional Chinese timber frame with column aspect ratio 0.14, only two initial modes (rest and pure-rock), which were mutually exclusive, appeared in the initial response. The initial response study presented here provides a theoretical route to the dynamic response of traditional Chinese timber structures for earthquake hazard mitigation and structural health monitoring.
       
  • Composite Action Assessment of Concrete-Filled FRP Tubes Subjected to
           Flexural Cyclic Load
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Ahmed M. Ali, Radhouane MasmoudiAbstractConcrete filled fiber-reinforced polymer (FRP) tubes (CFFT) is a principal competitor to replace the conventional reinforced concrete (RC) members in severe environmental conditions. This paper investigates the composite action (interfacial bond) between the FRP tube and its concrete core. Four full-scale CFFT columns associated with RC footings were tested under lateral cyclic load without axial load. Two different diameters of CFFT columns were tested to study the size effect on the bond performance then consequently on the flexural behavior of the CFFT column. The interior surface of two FRP tubes have been covered by sand coating to improve the interfacial bond between the FRP tube and the concrete core. A new approach was proposed to evaluate the composite action between the FRP tube and the concrete core based on measuring strains inside the concrete core by using embedded concrete strain gauges. The assessment of the composite action between the FRP tube and the concrete core was implemented by comparing the interior concrete strains and the corresponding strains on the external tube skin. The experimental results illustrated that the bond significantly influences the flexural strength and stiffness of the CFFT column. Increasing the tube diameter leads to reduce the interfacial bond between the FRP tube and its concrete core. Using sand-coating as a bond enhancer improved the bond between the FRP tube and the concrete core, minimize the adverse effect of increasing the tube diameter, and increased the flexural capacity and stiffness of tested CFFT columns. An analytical model was developed to estimate the flexural capacity of the fully bonded CFFT member.
       
  • Probabilistic prediction of mechanical characteristics of corroded strands
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Jaebeom Lee, Young-Joo Lee, Chang-Su ShimAbstractSteel strands are widely used as important structural members of bridges. Their failure can be detrimental to the structure; therefore, various studies on predicting their mechanical characteristics have been conducted. However, explaining the mechanical characteristics of steel strands is difficult because of geometric complexity, difficulty in corrosion modeling, and various uncertain factors. This paper proposes a new method for the probabilistic prediction of the mechanical characteristics of corroded steel strands. First, finite element (FE) models are built for several types of corroded wires. Second, based on the FE analysis results, a nonparametric surrogate model is constructed using Gaussian process regression. Third, the ultimate strength and strain of the corroded steel strands are predicted probabilistically by conducting a Monte Carlo simulation with a theoretical strand model. As a result, the probabilistic ranges of 50% and 95% are estimated. Based on the prediction results, appropriate probabilistic distributions for the ultimate strength and strain are studied. The proposed method is applied to several specimens of corroded seven-wire strands. The prediction results are in good agreement with the test results. Additionally, a failure probability assessment is conducted as an application example based on the goodness-of-fit test.
       
  • Modal analysis method for tensegrity structures via stiffness
           transformation from node space to task space
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Xin Li, Jingfeng He, Mantian Li, Hongzhou Jiang, Yunqi HuangAbstractA tensegrity structure is a type of hybrid soft-rigid system, whose high compliance is prone to induce an oscillatory motion. The oscillatory characteristics can be exploited to control a tensegrity structure efficiently, and modal analysis is beneficial in guiding the exploration of the oscillatory characteristics of this type of structures. We derive node-based modes of tensegrity structures using the finite element method. By freezing the substructures as a rigid body, the node-based stiffness is converted into a task-space stiffness, during which the elasticity within the substructures is filtered out from the final modal analysis results. Compared with the node-based modal analysis results, the transformation method proposed in this paper significantly reduces the mode dimension. Concurrently, the low-order modes almost remain unchanged when the stiffness of the substructures is much higher than that of the interconnecting cables. We select two tensegrity structures as examples to demonstrate our method.
       
  • Partially corroded reinforced concrete piers under axial compression and
           cyclic loading: An experimental study
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Haijun Zhou, Yanan Xu, Yanrong Peng, Xuebing Liang, Dawang Li, Feng XingAbstractTwelve reinforced concrete (RC) pier specimens were developed and partially corroded to simulate severe corrosion in splash and tidal zones. Six target corrosion levels were applied to rebars and stirrups using an electrochemical accelerated corrosion technique. Axial compression loading and cyclic loading tests were carried out with six specimens per group. The test results showed that mechanical parameters of pier specimens degraded with an increase in corrosion. The ultimate load, ductility factor, energy dissipation decreased by 29.96%, 9.26%, 67.44% for axial compression specimen with 15.82% rebar mass loss compared to those of intact specimen; for cyclic loading specimens, they decreased by 10.69%, 21.47%, 57.46% with 15.71% rebar mass loss, respectively. Comparative analysis showed that the difference for the degradation level of dimensionless parameters was not obvious between axial compression loading and cyclic loading tests. Findings also showed that for severely corroded specimens, the plastic hinge zone transferred from the bottom of RC piers to the splash and tidal zones. Although the extent of the degradation of the results between the published paper and this test shows significant variations; degradation of dimensionless energy dissipation was always the most serious one.
       
  • A series of forecasting models for seismic evaluation of dams based on
           ground motion meta-features
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Mohammad Amin Hariri-Ardebili, Sasan BarakAbstractUncertainty quantification (UQ) due to seismic ground motions variability is an important task in risk-informed condition assessment of infrastructures. Since performing multiple dynamic analyses is computationally expensive, it is valuable to develop a series of forecasting models based on the unique ground motion characteristics.This paper discusses the application of six different machine learning techniques on forecasting the structural behavior of gravity dams. Various time-, frequency-, and intensity-dependent characteristics are extracted from ground motion signals and used in machine learning. A large set of about 2000 real ground motions are used, each includes about 35 meta-features. The major outcome of this study is to show the applicability of meta-modeling-based UQ in seismic safety evaluation of dams. As an intermediary result, the advantages of different machine learning algorithms, as well as meta-feature selection possibility is discussed for the current dataset. This paper proposes a feasibility study to reduce the computational costs in UQ of large-scale infra-structural systems.
       
  • Polynomial chaos expansion for uncertainty quantification of dam
           engineering problems
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Mohammad Amin Hariri-Ardebili, Bruno SudretAbstractUncertainty quantification is an inseparable part of risk assessment in dam engineering. Many probabilistic methods have been developed to deal with random nature of the input parameters or the system itself. In this paper, the polynomial chaos expansion (PCE) is adopted as an effective technique for uncertainty quantification of variety of dam engineering problems (specially with small data sets). Four different case studies are investigated with increasing complexities in which the static and dynamic responses are sought to predict. The limit state functions in the form of implicit and explicit are studied. Uncertainties are propagated in material properties and modeling. Depending on the problem at hand, a validation set from several thousands to couple of hundreds are used. Overall, it is found that the PCE is an effective technique to deal with uncertainty quantification in concrete dams.
       
  • Reliability analysis of footbridges pre-tensioned with carbon fiber
           reinforced polymer tendons under flexural loading
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Sophia Kueres, Josef HeggerAbstractA common problem of concrete bridges is corrosion damages of the steel reinforcement. The related loss of capacity as well as visual effects often require expensive and elaborate refurbishment or even reconstruction. To overcome these drawbacks, the application of non-corrosive fiber reinforced polymer (FRP) reinforcement in concrete structures has been established and investigated throughout the last three decades. The successful application of prestressed carbon fiber reinforced polymer (CFRP) reinforcement in bridge constructions was demonstrated by several projects realized in the United States and Canada. Nevertheless, despite the successful realization of these projects, a widespread application has not yet been possible due to the lack of consistent and approved design regulations. In Germany and Europe, the use of FRP reinforcement in bridge construction is even limited to individual cases and non-prestressed reinforcement. Thus, further investigations are necessary to develop a comprehensive guideline for the design of members with pre-tensioned CFRP tendons in compliance with current codes of practice.In order to achieve this objective, a flexural design model for the design of bridge girders prestressed with CFRP reinforcement was developed. In this paper, the reliability analysis of the flexural design model applied to a modular footbridge system pre-tensioned with CFRP tendons is presented. Stochastic simulations are conducted to evaluate the safety of the developed footbridge concepts and to determine an appropriate partial safety factor for the CFRP tendons. For this purpose, the reliability requirements according to the specifications of Eurocode 0 (EC0) are analyzed and evaluation benchmarks are defined to allow for a sufficient reliability of the bridges. The statistical characteristics of the variable parameters needed for the analysis were defined based on a literature review and own investigations.
       
  • Benefits of inclined pile foundations in earthquake resistant design of
           bridges
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Francisco González, Sandro Carbonari, Luis A. Padrón, Michele Morici, Juan J. Aznárez, Francesca Dezi, Orlando Maeso, Graziano LeoniAbstractThis paper studies the effects of the use of inclined pile foundations on the seismic response of bridges, and shows that this type of foundation is able to promote significant reductions in the ductility demand of reinforced concrete piers. To this end, a set of nine multi-span roadway viaducts with different pier heights and span lengths is defined. Each configuration is designed and dimensioned in detail following a displacement-based approach, considering both linear and non-linear expected behaviours and assuming different target ductilities for piers. The systems are assumed to be founded on a specific soil profile, and suitable pile foundation layouts and dimensions are determined for each case, with four different pile rake angles (including the vertical case) in each configuration. Soil-structure interaction phenomena are incorporated through the corresponding frequency-dependent impedance functions and kinematic interaction factors. The transverse response of the viaducts, subject to a set of seven suitable scaled real accelerograms, is computed and analysed making use of a substructuring approach and non-linear time-domain analysis in which a lumped parameter model is adopted to represent the foundation response. Results, presented not only in terms of ductility demand but also of energy dissipated in the structural system by damping or by yielding, suggest that inclined piles are clearly beneficial to the seismic response of bridges, contributing to significant reductions in ductility demand due to the particular kinematic seismic response of this type of foundations and associated reductions in the input seismic energy to the system.
       
  • Instability characteristics analysis of a simply supported cylindrical
           shell subjected to swirling annular flow of viscous fluid
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Wen-Bo Ning, Minglin Shi, Suqin Jiang, Yundong Li, Mingjun ZhongThe instability characteristics of an out cylindrical shell subjected to an annular flow, where the fluid is flowing through the annulus between the inner shell and the outer shell, are investigated based on the zero-level contour method and the travelling wave solutions. The inviscid fluid-dynamic forces, related to shell vibrations, are determined by the potential flow theory. The time-mean Navier-Stokes equations are utilized to obtained steady viscous forces based on the fully developed turbulent flow theory. The Flügge's thin shell theory is used for shell motions. Adopting the zero-level contour method and the Galerkin's method, the behaviors of losing stability of the flow-shell system are given and physical reasons for the instability of the system are explained. Detailed studies are performed in order to elucidate quantificationally the effects of pre-loads related to the steady viscous forces, geometry parameters on the loss of stability. Especially, the influence of the swirl number on the instability characteristics of the system is discussed.Graphical abstractThe swirl lowers the stability of the fluid-shell system and the two critical fluid velocities decline with the increase of the swirl number. The form of the stability loss of such system does not change when the swirl number grows considerable big.Graphical abstract for this article
       
  • Seismic mitigation performance of structures with viscous dampers under
           near-fault pulse-type earthquakes
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Gaoxing Hu, Yanan Wang, Wei Huang, Bin Li, Bin LuoAbstractThis study is aimed at clarifying the seismic mitigation performance of structures with fluid viscous dampers (FVDs) as a function of the characteristics of the near-fault pulse-type (NP) ground motion and the structural dynamic properties. For this purpose, the response spectra and energy response of single-degree-of-freedom (SDOF) structures with FVDs subjected to 20 NP ground motions with different pulse periods Tp are discussed. The seismic response and energy dissipation distribution of multi-degree-of-freedom (MDOF) structures with FVDs are also investigated and compared with those of SDOF structures. The results revealed that although the presence of FVDs produces significant improvements in the seismic response of the structures, the structure may still experience large plastic deformation, which always occurs when T/Tp is less than ‘1’ and T1/Tp is greater than ‘1’, T and T1 being pre-earthquake and post-earthquake structural periods. For short period structures (multi-storey) with FVDs, the plastic deformation can be further slightly reduced by making T/Tp and T1/Tp less than ‘1’ at the same time, so that the structure can be basically kept within the elastic range. However, the intermediate and long period structures (mid-rise and high-rise) with FVDs are more likely to experience large plastic deformation when T/Tp is less than ‘1’, and the floor shear forces may be slightly reduced or even obviously amplified. Furthermore, the current research findings on SDOF structures with FVDs may not be extended directly to MDOF structures with FVDs due to the more complex dynamic properties of MDOF structures.
       
  • Shallow buried RC structures behavior under airblast in the time and P-I
           domains
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Kay Hyang Chee, Theodor Krauthammer, Serdar AstarliogluAbstractThe behavior of shallow-buried reinforced concrete box structures under the effects of airblast load is of interest. Analyzing such complicated nonlinear behavior would typically require advanced numerical computer codes, and extensive computational resources. Therefore, developing simplified, physics-based, numerical approaches that could be used for expedient numerical analyses, in support of design and/or assessment of shallow-buried RC structures is of great interest. A numerical method for the dynamic analysis of the box structure was developed, based on the Single-Degree-of-Freedom (SDOF) approach. The effects of the roof slab’s flexural and direct-shear modes of response were combined with the effects of compressive and tensile membrane actions in reinforced concrete slabs under externally-applied in-plane thrust on the resistance functions were addressed in the study. Soil-structure interaction, in terms of soil arching effect, on the load distribution and reduction also were addressed. The resistance functions for each structural response mode of the structure were generated and used in the SDOF dynamic analysis and the corresponding load-impulse (P-I) diagrams. A rational model was proposed to incorporate varying SDOF equivalent load and mass factors in relation to the resistance function. The results were derived in the time and P-I domains, and were validated using available experimental data that had been obtained by other investigators.
       
  • Constructal Design for the ultimate buckling stress improvement of
           stiffened plates submitted to uniaxial compressive load
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): João Paulo Silva Lima, Marcelo Langhinrichs Cunha, Elizaldo Domingues dos Santos, Luiz Alberto Oliveira Rocha, Mauro de Vasconcellos Real, Liércio André IsoldiAbstractSeveral engineering structures used in civil, aeronautical and, mainly, naval and offshore industries consist of steel stiffened panels formed by beams welded into thin plates. These beams are called stiffeners, being arranged longitudinally and/or transversely aiming to increase the mechanical strength of the plate. So, it is desirable to obtain an optimal geometric configuration for these structures which maximizes its ultimate buckling stress. In this context, it has been used the Constructal Design Method associated with the Exhaustive Search technique and the Finite Element Method (by ANSYS software) in a geometric optimization study of plates with stiffeners subjected to elasto-plastic buckling. Initially, it was adopted a simply supported thin plate without stiffeners (called reference plate), using its ultimate buckling stress as a reference value for the study. After that, part of its volume has been transformed into stiffeners, which were incorporated into the plate. For this, the volume fraction (ϕ) parameter, which represents the ratio of the volume of stiffeners (Vs) and the total volume of the structural element plate/stiffeners (VT), has been adopted, without varying the final volume of the plate. Moreover, the number of longitudinal (Nls) and transverse (Nts) stiffeners, as well as the ratio between the height of the stiffener and its thickness (hs/ts), were considered as degrees of freedom. The study considered two total steel volume values VT1 = 0.040 m3 and VT2 = 0.028 m3. The results indicated that the variation of the geometrical configuration significantly affects the mechanical behavior of stiffened panels under buckling. Therefore, it was possible to determine the optimum geometry that leads to a maximized ultimate buckling stress, near the yield strength of the material. The stiffened plates with volume VT1 did not present relevant improvements if compared with the reference plate, since the optimal geometry achieved an improvement of 7.38% concerning the ultimate buckling stress of the reference plate. On the other hand, the study of the plates with volume VT2 showed significant improvements in the value of the ultimate buckling stress, so that the optimized geometric configuration among all analyzed geometries reached an improvement of 88.50% when compared with the ultimate buckling stress of the reference plate.
       
  • Load identification for a viscoelastic solid by an accurate meshfree
           sensitivity analysis
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): B. Jamshidi, M.R. Hematiyan, M. Mahzoon, Y.C. ShiahAbstractThis article presents a novel inverse method for identification of a space- and time-dependent load, applied to a two-dimensional viscoelastic solid. Measured strains at several points are considered as sampling quantities. An improved meshfree radial point interpolation method is employed to solve the direct problem. The inverse problem is treated by an optimization approach, where the cost function is described in terms of the differences between measured and computed strains. The damped Gauss Newton method is utilized to solve the inverse problem. A new approach for the sensitivity analysis based on direct differentiation of governing equations is presented. The Tikhonov regularization method is employed to eliminate the undesired oscillations of the solutions of the inverse problem. Using a method based on the condition number of the sensitivity matrix, an appropriate configuration for sensors is determined. The effects of the location and the number of sensors on the accuracy of the identified loads are investigated. The robustness of the presented method to handle noisy measured data is investigated too.
       
  • Cyclic loading test of steel coupling beams with mid-span friction dampers
           and RC slabs
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Zhe Qu, Xiaodong Ji, Xiao Shi, Yandong Wang, Hanquan LiuAbstractIn coupled wall systems, coupling beams distributed along the structural height are intended to yield and dissipate seismic energy under moderate and severe earthquakes. The use of specifically designed dampers in coupling beams can greatly enhance the seismic performance of a structure. In the present study, a friction damper incorporating brake pad-to-mild steel friction interfaces is proposed for installation in a steel coupling beam at the mid-span. Cyclic loading tests were conducted on the friction coupons and subassemblages of steel coupling beams with mid-span friction dampers. An RC slab, which rested on the top flange of the steel coupling beam without shear connectors, was included in one of the subassemblage specimens. The test results show that the friction dampers exhibited stable and full hysteretic responses with up to 8% chord rotation of the coupling beams. The friction coefficients were gradually increased and the clamping forces of the dampers relaxed during the cyclic loading. The average friction coefficient was close to the nominal value with a small deviation. However, the unintended out-of-plane bending of the steel teeth of the friction dampers reduced the effective normal force on the friction interfaces and, thus, led to a lower-than-expected shear strength of the damper. Though not composited with the steel coupling beam, the RC slab sustained severe flexural cracks as wide as 6 mm at 4% chord rotation of the coupling beam and, thus, might influence the postquake recovery of a building. A simple numerical model was established to investigate the respective contribution of each part of the coupling beam. The results show that the post-sliding stiffness introduced by the RC slab was less than 1% of the initial stiffness of the coupling beam and decreased rapidly with increasing deformation amplitudes. The shear force in the slab exceeded 10% of the strength of the friction damper at 4% chord rotation and is deemed to be a potential source of overstrength for the design of a coupling beam and the surrounding elements.
       
  • Dynamic characteristic analysis and shaking table test for a curved
           surface isolated structure
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Kun Tian, Wenguang Liu, Demin Feng, Qiaorong YangAbstractTo reduce the displacement of an isolation layer, an innovative curved surface isolated structure (CSIS) system was put forward by using the curved surface characteristics of the isolation layer and the weight of the structure. Firstly, a simplified analysis model with multiple isolators considering the rotation of the upper structure around the center of curvature of the isolation layer and the oscillation around the center of the isolation layer was established. Subsequently, two CSIS models, with 4 degrees inclined isolators and 8 degrees inclined isolators, separately, were produced and a shaking table test was conducted. For comparison purpose, a normal isolated structure (NIS) model and a non-isolated structure (NS) model were also tested. The dynamic characteristics, acceleration and displacement responses of different models are compared and discussed. Finally, finite element models of the CSIS were established by using the software ABAQUS and the numerical simulation results were compared with the test results. The results show that the displacement responses of a CSIS are reduced and the CSIS can return to the initial position faster than the NIS; the acceleration response of a CSIS is slightly increased relative to the NIS, but significantly reduced compared to the NS; the acceleration time-history curves of each floor and the displacement time-history curves of the isolation layer for numerical simulation results show good agreement with experimental data.
       
  • Numerical simulation of beam-to-column connections in precast reinforced
           concrete buildings using fibre-based frame models
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Romain Sousa, Nádia Batalha, Hugo RodriguesAbstractRecent earthquakes exposed the poor performance of precast RC structures, imposing damage on both structural and non-structural elements. The concentration of damage at the beam-to-column connections highlights the vulnerability of these systems and the need to understand and improve its seismic performance. The numerical simulation of connection systems in efficient software packages has been addressed in the past by several authors. However, these models fail in describing the different mechanisms independently and, therefore, are difficult to apply to generic connection solutions. Once identified the main lateral load resisting mechanisms involved, a new numerical model is proposed accounting for friction, dowel behaviour and the contribution of the neoprene components. The proposed model was validated against different experimental tests and a parametric study was performed to understand the contribution of the different components, especially in what concerns to the maximum horizontal strength and hysteretic energy dissipation.
       
  • Study on compressive bearing capacity and axial stiffness of welded hollow
           spherical joints with H-shaped steel member
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Xiangyu Yan, Yan Duan, Yuxuan Zhang, Zhihua Chen, Qiwu ZhangAbstractTo study the compressive bearing capacity and stiffness of welded hollow spherical joints with H-shaped steel member(WHS-HSM joints), axial compression test was conducted on eight specimens of WHS-HSM joints. By verifying the correctness of the numerical model, the parametric analyses were done considering the following factors, such as the welded hollow sphere diameter (D), the wall thickness of the welded hollow sphere (t), and the height (h) and width (b) of the H-shaped steel member(HSM). The calculation methods of the compressive capacity and axial stiffness of WHS-HSM were proposed. The results show that the failure mode of the joints under axial compressive load is the hollow sphere’s concave failure starting from the flange edge of H-beam. Under axial compressive load, the joints show good ductility. The bearing capacity and initial axial stiffness of the joints are positively related with the wall thickness of the welded hollow sphere (t), the section height(h) and width(b) of HSM, but are negatively correlated with the diameter(D) of the welded hollow sphere. The formulas for calculating the compressive bearing capacity and initial axial stiffness proposed in this paper have high accuracy.
       
  • Response attenuation of cable-stayed bridge subjected to central US
           earthquakes using neuro-fuzzy and simple adaptive control
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Rachel W. Soares, Luciana R. Barroso, Omar A.S. Al-FahdawiAbstractCable-stayed bridges generally present high flexibility, little redundancy, and complex dynamic behavior, which may lead to excessive dynamic responses. Structural control is an option to limit dynamic responses of these structures in order to avoid excessive damage and guarantee an acceptable level of comfort. Most studies in the field of control of cable-stayed bridges are performed considering their nominal parameters. However, bridges are subjected to extreme changes in temperature, cracking, corrosion, snow accumulation, extreme loading and fatigue. Additionally, engineering modeling simplifications, estimates, and assumptions also result in estimation of parameters that are different from the actual ones. Earthquake excitation prediction also involves a great amount of uncertainties. The development of a control scheme that presents satisfactory performance and presents enough robustness is fundamental for its successful operation. The main goal of this study is to find control solutions that are able to attenuate seismic induced responses, while providing enough predictability and robustness in face of parametric changes and the variability of earthquake loads. The implementation of a control approach that is cost effective, dependable, predictable and effective may lead to the possibility of accounting for this control solution in design, allowing for more flexible but safe structures. A control approach that is dependable and robust has the potential to guarantee performance limits and impact how structures are designed in the future. Adaptive control is presented in this research as a suitable and robust control alternative to deal with the many uncertainties related to the prediction of bridge structural parameters and earthquake loading. Adaptive control schemes based on the simple adaptive control and the neuro-fuzzy adaptive control theoretical basis are proposed to attenuate the seismic responses of the benchmark for cable-stayed bridges, considering different parametric scenarios, as well as site conditions and seismic characteristics of the central US region. The performances of the adaptive schemes are compared to non-adaptive control before and after two parametric variations are introduced to the bridge, considering earthquakes matched to the American Association of State Highways and Transportation Officials’ most recent design spectra. Probability density functions are developed in order to capture the controlled performance representative of the earthquake suite. The adaptive methods performances are compared to uncontrolled and passive schemes before and after two parametric variations are considered. The bridge controlled by the passive-on case presents a satisfactory performance for the nominal structure. However, once the parameters are changed, the performance of the control scheme deteriorates. The passive-off scheme sustains performance well; however, the control scheme does not reduce overall responses significantly. The neuro-fuzzy control displays improved performance in comparison to the passive cases. The simple adaptive control scheme gives an overall successful reduction in both peak and normed responses, sustaining performance for most criteria and shows improved performance and robustness compared to the other schemes.
       
  • Designing efficient grid structures considering structural imperfection
           sensitivity
    • Abstract: Publication date: Available online 29 November 2019Source: Engineering StructuresAuthor(s): Fengcheng Liu, Ruoqiang Feng, Konstantinos Daniel Tsavdaridis, Guirong YanAbstractAt the initial design stage of a grid structure, shape optimisation is an effective way to find the optimal structural form. However, most of the shape optimisation methods do not take into consideration the imperfections, thus the actual buckling load capacity of the optimised structure is usually low. In this paper, an improved shape optimisation method is proposed, one that is considering the effect of structural imperfection sensitivity. In this method, the bending strain energy ratio is taken as a constraint, and when the total strain energy decreases, yet there is a certain proportion of bending strain energy in the structure. Consequently, the resulted shape is not sensitive to the initial geometry imperfection, and therefore, an efficient structure with higher buckling load capacity and low imperfection sensitivity is obtained. In order to evaluate the redundancy performance of the optimised structure, an index called structural overall redundancy, based on damage model is proposed herein. The damage model is simulated by removing a key rod of the structure. The results demonstrate that the overall redundancy of the structure obtained by the proposed method is higher than that obtained by the traditional method, thus an optimal design of a grid structure is obtained.
       
  • Numerical out-of-plane stability analysis of long span timber trusses with
           focus on buckling length calculations
    • Abstract: Publication date: Available online 29 November 2019Source: Engineering StructuresAuthor(s): Petr Sejkot, Sigurdur Ormarsson, Johan Vessby, Bo KällsnerAbstractAccording to the harmonized European design code for timber structures, Eurocode 5, all pitched timber trusses are designed as an in-plane structure, meaning that the bracing systems used are assumed to prevent the out-of-plane failure of the truss if sufficient strength and stiffness are provided. The present paper studies how the stiffness of a wooden bracing system contributes to the out-of-plane stability of a trussed roof structure. Results from numerical simulations indicate that significant bracing forces may occur in compressed structural members for long-span timber structures. As well, the values obtained from the calculations according to Eurocode 5 are occasionally far from the results obtained by numerical simulations.
       
  • Design recommendations for stainless steel I-sections under concentrated
           transverse loading
    • Abstract: Publication date: Available online 29 November 2019Source: Engineering StructuresAuthor(s): G.B. dos Santos, L. GardnerAbstractRecent investigations have highlighted the need for improved provisions for determining the resistance of stainless steel I-sections under concentrated transverse loading. Such provisions, which reflect the particular characteristics of the material, have been developed and are described herein. A review of the existing European design formulae for members under concentrated transverse loading is firstly presented. Then a series of parametric studies, based on validated finite element models are described covering I-sections with a range of web slenderness values and different stainless steel grades. On the basis of the numerical results, together with existing experimental data, revised design equations are presented and assessed through reliability analysis performed in accordance with Annex D of EN 1990. The new provisions yield enhanced ultimate load predictions and are expected to be included in the next revision of EN 1993-1-4.
       
  • Shear buckling strength of web-posts in castellated steel beams in fire
    • Abstract: Publication date: Available online 28 November 2019Source: Engineering StructuresAuthor(s): Larice Gomes Justino, José Carlos Lopes Ribeiro, Gustavo de Souza Veríssimo, José Luiz Rangel Paes, Leonardo Gonçalves PedrotiAbstractMost existing formulations for determining shear strength due to web-post buckling by shear (WPBS) in castellated steel beams depend on many variables, are not applicable to fire situation or do not have a normative approach. In order to provide a simpler and more practical formulation, also applicable to the fire situation, this study presents a semi-empirical formulation based on numerical results of validated models, considering the hypothesis of uniform temperature distribution along the profile and the analogy between the strut model and the compressed diagonal of a web-post subject to WPBS. This semi-empirical model is based on the formulation of EN 1993-1-2:2005 and ABNT NBR 14323:2013 to obtain the resistance of compressed members at elevated temperatures and it is applicable to Litzka, anglo-saxon and Peiner type castellated beams.
       
  • Shear strength estimation of masonry walls using a panel model
    • Abstract: Publication date: Available online 28 November 2019Source: Engineering StructuresAuthor(s): Leonardo M. Massone, Daslav F. OstoicAbstractMasonry walls are structural elements generally used in housing or small buildings. Given their structural configuration, they commonly present shear failure due to seismic actions, characterized by a fragile response. Thus, it is important to have simple, yet reliable tools that correctly estimate the shear capacity of walls. For that, a simple existing model developed for reinforced concrete elements and based on a panel model is used and adapted to masonry walls, providing a novel formulation that can be applicable to both materials. For compression and tension behavior, the prismatic resistance of the panel is used, which, due to the anisotropy of the material, degrades with the angle formed by the load with the vertical mortar joint. Strain values are set for compression and tension failure modes, and a degradation coefficient in compression due to the biaxial strain loading is included. Additionally, bond failure is also incorporated into the model. A database of 41 tests of reinforced masonry walls and 12 tests of confined masonry walls is used for model validation. The strength ratio between the shear strength obtained by the model and the test is compared, giving an average and a coefficient of variation (COV) of 1.0 and 0.15, respectively for reinforced walls, and 1.08 and 0.14 for confined walls, showing a satisfactory performance and better behavior than simple models from the literature. The analysis of general trends of the strength ratio reveals that there is a low dependence between the strength ratio and the studied parameters, implying that the model captures the physical behavior of masonry walls.
       
  • Dynamic analysis of laminated piezoelectric cylindrical shells
    • Abstract: Publication date: Available online 27 November 2019Source: Engineering StructuresAuthor(s): Yunying Zhou, Jun Zhu, Dongying LiuAbstractThe method of reverberation-ray matrix (MRRM) has been successfully utilized to study the transient waves in beams, plates and laminated solids. In this work, the MRRM is adopted to study the transient responses and wave propagation of piezoelectric cylindrical shells with finite size. Based on the Donnell shell theory, the reverberation matrix formulation in the cylindrical shell is derived. Using Laplace transformation, the transient responses under imposed impact load can be predicted. Through the numerical simulations, the early short time transient responses can be further elucidated. Furthermore, the effects of the geometric parameters of the composite shells on the wave propagating in the laminated piezoelectric shells are also analyzed.
       
  • Experimental and numerical investigation of usp for optimization of
           transition zone of railway
    • Abstract: Publication date: Available online 27 November 2019Source: Engineering StructuresAuthor(s): Yusuf Çati, Sercan Gökçeli, Özgür Anil, Canan S. KorkmazAbstractTo meet the increasing demands and be competitive in the market, railway systems must be sustainable. One of the important criteria for sustainability is to have lower life cycle costs (LCC). Several statistics report higher track geometry degradation in transition zones, and maintenance of these zones has a large share in LCC. One of the reasons behind the accelerated track degradation is the wear and the breakage of ballast in transition zones due to sudden stiffness changes and ballast vibrations. Optimized track support solutions can have a positive impact on track degradation in transition zones. Under sleeper pads (USP) as supporting elastic elements are being used to decrease stress and vibration on the ballast. In this study, numerical models with and without USP components are built for the selected transition zone. Numerical models simulate dynamic load from train passages and impact hammer load. Thus, the USP component effect on vibrational behavior of the track is analyzed. For the validation of simulations, several experiments were carried out on the selected transition zone. In addition to them, vibration mitigation experiments were performed. According to the simulation and experimental outcomes of the study, the developed models are satisfactorily in compliance with experimental results. It has been observed from simulation results that the integration of the USP component into track provides an approximately 25% decrease in ballast acceleration. On the other hand, it has a negative effect on rail and sleepers by increasing their vibration. Since this is an expected outcome of USP, the methodology in the study can be beneficial in the design phase.
       
  • Statistical modelling of seismic vulnerability of RC, timber and masonry
           buildings from complete empirical loss data
    • Abstract: Publication date: Available online 27 November 2019Source: Engineering StructuresAuthor(s): Bjarni Bessason, Jón Örvar Bjarnason, Rajesh RupakhetyAbstractIn June 2000 two shallow, strike slip, Mw6.5 earthquakes occurred in the middle of the largest agricultural region in Iceland. The epicentres were close to small towns and villages and almost 5000 residential buildings were affected. A great deal of damage occurred but no residential buildings collapsed and there was no loss of life. Insurance against natural disasters is compulsory for all buildings in Iceland and they are all registered in a comprehensive official property database. Therefore, to fulfil insurance claims, a field survey was carried out after the two earthquakes where repair cost was estimated for every damaged building. By combing the loss data with the property database it was possible to establish a complete loss database, where all residential buildings in the affected area were included, both buildings with loss as well as buildings with no-loss. The main aim of the study was to fit a statistical vulnerability model to the data. Due to the high proportion of no-loss buildings in the database (~84%) a new and novel vulnerability model was used based on a zero-inflated beta regression model. The model was fitted to the three main building typologies in the affected region, i.e. low-rise structural wall RC, timber, and masonry buildings. The proposed model can be used to predict the mean and desired prediction limits of the losses for a given intensity level as well as to create fragility functions. All the typologies showed outstanding performance in the two destructive earthquakes, which is important to report, model and learn from.
       
  • Impact of horizontal soil strain on flexible manhole riser deflection
           based on laboratory test results
    • Abstract: Publication date: Available online 26 November 2019Source: Engineering StructuresAuthor(s): Magdalena Zięba, Piotr KaliszAbstractUnderground mining extraction causes deformation of the rock mass and the surface, which may cause damage to the construction of manholes, thus leading to the failure of the sewage system. To ensure the proper operation of sewer systems in mining areas, it is important to consider the interaction between the manhole and the horizontally strained soil. The impact of continuous mining deformations of the ground around the manhole manifests itself through the impact of horizontal strains, which mainly affect the manhole riser. These strains cause the horizontal cross-sectional deflection of the flexible manhole riser, which is made of thermoplastics.This article presents the results of laboratory (model) tests conducted in conditions similar to in-situ conditions. The aim of these studies was to determine the impact of horizontal strains of the non-cohesive soil on the relative deflection of the horizontal cross-section of the manhole riser, which was made of thermoplastic. The laboratory tests have been performed for manhole riser models with various ring stiffnesses, which are used in practice, and at various manhole foundation depths. The values of the relative cross-sectional deflection of the manhole riser models have been determined for both the horizontal loosening and horizontal compaction of the soil. The research methodology has been presented, and the results of laboratory tests have also been analysed. The horizontal cross-sectional deflection of the flexible manhole riser depends not only on the values of the horizontal soil strain but also on the ring stiffness and the foundation depth of the discussed cross-section of the riser.
       
  • Progressive collapse resistance of steel self-centering MRFs including the
           effects of the composite floor
    • Abstract: Publication date: Available online 26 November 2019Source: Engineering StructuresAuthor(s): Christoforos A. Dimopoulos, Fabio Freddi, Theodore L. Karavasilis, George VasdravellisAbstractThis paper presents progressive collapse simulations to assess the robustness of a seismic-resistant building using self-centering moment resisting frames (SC-MRFs) under a sudden column loss scenario. The first floor of the building, including the composite floor, was modelled in ABAQUS using a mixture of finite element types and simulation methods to balance computational cost and accuracy. First, key components of the numerical model, including the composite beams, the fin-plate beam-column connections, and the perimeter SC-MRFs, were validated against available experimental results to ensure a reliable simulation. The validated model was then used to study the robustness of the building under a sudden column loss event. Both nonlinear static and dynamic analyses were employed. The simulations allowed for the identification of all possible failure modes and the quantification of the contribution of the composite floor to the robustness of the frame. The results show that the building can withstand the code-prescribed load with a safety factor of 2 and that the structural limit state that triggers progressive collapse is the buckling of the gravity columns. The Dynamic Increase Factor (DIF) was also identified by comparing the static and dynamic responses.
       
  • Robust decision-making design for sustainable pedestrian concrete bridges
    • Abstract: Publication date: Available online 26 November 2019Source: Engineering StructuresAuthor(s): Vicent Penadés-Plà, Víctor Yepes, Tatiana García-SeguraAbstractIn recent years, there is a trend toward the construction of sustainable structures. The goal of sustainability in structures involves several criteria that are normally opposed, leading to a decision-making process. In this process, there is a subjective portion that cannot be eliminated, such as qualitative criteria assessment of and assigning criteria importance. In these cases, decision-makers become part of the decision-making process, assessing it according to their preferences. In this work, a methodology to reduce the participation of decision-makers in achieving the goal of sustainability in structures is proposed. For this purpose, principal component analysis, kriging-based optimization, and the analytical hierarchy process are used. Principal component analysis is used to reduce the complexity of the problem according to the highly correlated criteria. Kriging-based optimization obtains sustainable solutions depending on all the perspectives of sustainability. Finally, the analytical hierarchy process is applied to reduce the optimized sustainable solutions according to the decision-maker’s views. This methodology is applied a continuous concrete box-girder pedestrian bridge deck to reach sustainable designs. This methodology allows a reduction of the complexity of the decision-making problem and also obtains sustainable robust solutions.
       
  • Vibration-assisted installation and decommissioning of a slip-joint
    • Abstract: Publication date: Available online 26 November 2019Source: Engineering StructuresAuthor(s): Alessandro Cabboi, Maxim Segeren, Hayo Hendrikse, Andrei MetrikineAbstractThe structural failure of grouted connections for offshore wind turbines focused the industrial attention towards different and innovative solutions to guarantee a safe connection between the monopile foundation and the turbine tower. An alternative option to the traditional grouted joint is a direct steel-to-steel connection, also called a slip-joint which was sporadically used for onshore wind turbines. To such regard, a proof of concept is illustrated concerning a new installation and decommissioning technique of a slip-joint. The key aspect of the proposed method is to guarantee a proper fit and sound contact of the slip-joint by means of vibration-assisted settlements. Therefore, the effectiveness of applying a harmonic excitation during the installation and decommissioning procedure is experimentally investigated using a 1:10 scaled model of the slip-joint. During the dynamic tests, the applied static load and the settlements of the joint are monitored using load cells, displacement sensors and strain gauges placed both inside and outside the conical surfaces. For the installation tests, the results show that settlement occurs when applying a harmonic load at specific forcing frequencies. All the vibration-induced settlements tend to stabilize in time, indicating that a sound contact through vibration-assisted installation can be achieved. In a similar way, the decommissioning proved to be effective at certain forcing frequencies. According to all the tests performed during this experimental campaign, both the installation and decommissioning tests showed to be more sensitive to the forcing frequency rather than to the dynamic forcing amplitude.
       
  • A mixture distribution with fractional moments for efficient seismic
           reliability analysis of nonlinear structures
    • Abstract: Publication date: Available online 26 November 2019Source: Engineering StructuresAuthor(s): Chao Dang, Jun XuAbstractIn this paper, an efficient approach is proposed for seismic reliability analysis of nonlinear structures with random parameters subjected to non-stationary stochastic ground motions. First, the first-passage reliability problem is equivalently transformed to the evaluation of the extreme value distribution (EVD) of the response. A mixture of inverse Gaussian and Lognormal distributions (MIGLD) is then proposed to reconstruct the EVD in the entire distribution domain, where the fractional moments are suggested as constraints to specify the unknown parameters. Only five low-order fractional moments of the EVD are actually required in the proposed method due to the inherent advantages of fractional moments. Then, the recently developed Latinized partially stratified sampling (LPSS) approach, is introduced to evaluate the fractional moments of the EVD with a small sample size. In this regard, the EVD could be reconstructed accurately in the entire distribution domain with high efficiency, particularly in the distribution tail, and the corresponding failure probabilities can be obtained in a straightforward way. Two numerical examples involving both linear and nonlinear shear-frame structures under non-stationary stochastic seismic ground motions are investigated to verify the efficacy of the proposed approach. The results indicate that the proposed method can result in accurate seismic reliability of nonlinear structures with high efficiency.
       
  • Testing of insulated sandwich panels with GFRP shear connectors
    • Abstract: Publication date: Available online 26 November 2019Source: Engineering StructuresAuthor(s): Hetao Hou, Wenhao Wang, Bing Qu, Chunxue DaiAbstractThis paper focused on the panel which sandwiches an Expanded Polystyrene (EPS) layer between two Steel Reinforced Concrete Layers (SRCLs). The EPS layer provides thermal insulation in the panel while the two exterior SRCLs are connected by Glass Fiber Reinforced Plastic (GFRP) shear connectors to form the composite action and hence achieve a higher flexural resistance in the panel. Four types GFRP shear connectors which consist of diagonal web members, webs with circular perforations, webs with slotted perforations and solid webs, respectively, were considered in this research. To experimentally address the flexural responses of the panels with the four types of GFRP shear connectors, four full-scale experimental specimens were constructed and tested. The test results show that generally any of the four GFRP shear connectors can enable the panel to exhibit satisfactory flexural performance although the GFRP shear connectors with the solid webs tend to increase the ultimate flexural resistance of the panel. Beyond the experimental work, an analysis model based on the transformed cross-section approach and elastic beam theory was developed for capturing the flexural response of the panel up to the cracking limit state. Moreover, an analysis model based on the assumed strain and stress diagrams was established to compute the ultimate flexural resistance of the panel.
       
  • Full-scale test and numerical failure analysis of a latticed steel tubular
           transmission tower
    • Abstract: Publication date: Available online 26 November 2019Source: Engineering StructuresAuthor(s): Li Tian, Haiyang Pan, Ruisheng Ma, Lijuan Zhang, Zhengwei LiuAbstractUltimate capacity evaluation is of vital importance for electricity transmission tower-line systems, which are well recognized as the lifeline engineering in modern society. Undoubtedly, full-scale tests are the most effective and straightforward method for an in-depth understanding of the structural ultimate capacity. In the present study, full-scale tests of a latticed steel tubular transmission tower are performed with emphasis on the failure mechanism of the tower under extreme wind load. Structural responses, ultimate capacity and failure mechanism of the transmission tower in the tests are presented and discussed, respectively. Numerical simulations are then carried out to reproduce the failure of the transmission tower in the tests. In the finite element (FE) model, a buckling and softening failure model is developed to capture the behaviors of the transmission tower. Finally, numerical results are investigated and compared with those obtained in the full-scale tests. Experimental and numerical results demonstrate that the latticed steel tubular transmission tower is designed with enough capacity to resist the designed loads, and the buckling failures of leg members are the dominant cause of the collapse of the transmission tower. Additionally, the developed buckling and softening failure model can accurately reproduce the displacements, ultimate capacity and failure mechanism of the transmission tower. This research can extend the current state of knowledge concerning full-scale tests of latticed transmission towers, and provide a more comprehensive understanding of the performance of latticed steel tubular transmission towers under extreme loads.
       
  • Design method of structural retrofitting using viscous dampers based on
           elastic–plastic response reduction curve
    • Abstract: Publication date: Available online 26 November 2019Source: Engineering StructuresAuthor(s): Hua Shen, Ruifu Zhang, Dagen Weng, Qingzi Ge, Chao Wang, Md Mofakkharul IslamAbstractInstallation of viscous dampers has been demonstrated to be an effective method to perform seismic retrofitting of a structure. However, most of the existing design methods are based on the elastic stage of the primary structure. The proposed study presents an alternate method for retrofit design of a structure using viscous dampers whilst considering inelastic behaviour of the primary structure. The said method makes use of the elastic–plastic response reduction curve (EPRRC) to reflect the relationship between characteristic parameters of the viscous damper, supporting brace, and response of the viscous-damper-equipped primary structure. Use of this method ensures that reduction in storey drift as well as shear force is simultaneously realized within the EPRRC coincident reduction region. Thus, parameters concerning the required dampers and supporting braces can be obtained from EPRRC in accordance with target performances of the damped structure. Comparison between a traditional elastic response reduction curve (ERRC) and EPRRC indicates that ERRC tends to overestimate the performance of damped structures. Nonlinear time-history analysis was performed to verify the effectiveness of the proposed method when applied to a benchmark model. Additionally, probabilistic reliability of the said method was determined via incremental dynamic analysis. Results demonstrate that the proposed design method can effectively satisfy design requirements under different seismic intensities.
       
  • Collapse of steel-concrete composite frame under edge-column
           loss—Experiment and its analysis
    • Abstract: Publication date: Available online 26 November 2019Source: Engineering StructuresAuthor(s): Jing-Zhou Zhang, Guo-Qiang Li, Jian JiangAbstractPrevious studies on steel frames cannot consider the effect of concrete slabs on the collapse behavior of structures, while recent experimental studies on steel-concrete composite frames fail to fully mobilize the tensile membrane action in slabs and catenary action in beams which have great influence on the failure mode of the frame. Large-scale experiments are conducted in this study on steel frames with flat concrete slabs to investigate the resistance mechanisms and typical failure modes of the structure. An edge-column removal scenario is used to consider a worse condition than an internal-column removal case. The resistance-vertical displacement relationship at the column-removal location, horizontal displacements at the structural edges and final failure patterns of main structural components are reported. Parametric studies are conducted using a validated numerical model to further quantify the effect of concrete slab thicknesses, reinforcement diameters, and beam section dimensions on the collapse resistance of composite structures. A simplified calculation method is also proposed to predict the resistance-displacement curve of composite framed structures under an edge-column loss scenario. The experimental results show that even without external horizontal restraints, tensile catenary action and membrane action can significantly develop in the steel beams and concrete slabs, respectively, at large deflections of structures under an edge-column loss scenario. Positive yield lines are found to distribute diagonally in the slab extending from the column-removal location to the two corners of the slab, while negative yield lines elliptically distribute along the edges of the slab. The numerical results highlight that the contribution of tensile membrane action in concrete slabs to the collapse resistance is less significant than that of catenary action in steel beams. Moreover, increasing the section height of beams guarantees a greater plastic bearing capacity of composite structures, but it fails to always provide a larger ultimate bearing capacity due to a poorer ductility.
       
  • A time series based damage detection method for obtaining separate mass
           and stiffness damage features of shear-type structures
    • Abstract: Publication date: Available online 26 November 2019Source: Engineering StructuresAuthor(s): Ngoan T. Do, Mustafa GülAbstractOne of the main challenges in damage detection of in-service civil structures is the effect of operational and environmental changes. This paper presents a novel output-only vibration based method for detection of stiffness and mass changes in shear-type structures using a proposed time series analysis along with sensor clustering technique. AutoRegressive Moving Average models with eXogenous inputs (ARMAX) are incorporated with the equations of motion written for different sensor clusters. Together with two assumptions, changes in the ARMAX model coefficients are employed to build Stiffness Damage Features (SDF) and Mass Damage Features (MDF). Using SDFs and MDFs, existence, location, severity of changes, i.e., stiffness reduction due to damage, and changes in mass due to operational conditions, can be identified separately and accurately. To demonstrate the effectiveness of the proposed method in its current form, first, the shear-type IASC-ASCE numerical benchmark problem is employed. Subsequently, a laboratory-scale four-storey steel structure is developed and tested to study the proposed approach with experimental data. The results show that the approach can successfully identify the location and severity of damage and mass changes separately and very accurately using output-only vibration data.
       
  • Distributive relationship of anchorage force relative to reinforcement and
           headed bars
    • Abstract: Publication date: Available online 24 November 2019Source: Engineering StructuresAuthor(s): Tianming Miao, Wenzhong ZhengAbstractWhen using headed bars, the distributive relationship of anchorage force between reinforcement and headed bars is crucial. This study conducted pull-out tests on 120 specimens, categorized into 24 groups, with a cross-sectional area of 150 × 150 mm, and the parameters considered were diameter (d), yield strength of reinforcement (fy), embedment length (lah), and strength grades of concrete (fcg). The corresponding programs were proposed and verified based on test results. The concept of a stable development length (las) was proposed as the critical length to determined whether the headed bars entered a working state. An analysis indicated that the ratio of las to d increased linearly with the ratio of fy to the tensile strength of concrete (ft,m), and decreased nonlinearly with the ratio of the protective thickness (c) to d. A formula was established for las using two independent variables. las and the critical development length (lac) were determined to be 1.28 times and 0.66 times the general development length (la), respectively. A further analysis demonstrated that the ratio of the pressure of headed bars (Fp) to fy and the ratio of lah to las were only related to the ratio of c to d. Thus, the distributive relationship of the anchorage force between the reinforcement and the headed bars was obtained.
       
  • 3D small strain large deflection beam shape sensing including poisson
           effect
    • Abstract: Publication date: Available online 24 November 2019Source: Engineering StructuresAuthor(s): Pierre-Loup Schaefer, Grégory Chagnon, Alexandre Moreau-GaudryAbstractThis article presents a new method to monitor beam shapes from strain measures. The beam is instrumented with strain sensors placed on its surface with an angle of orientation. The method developed is a 3D large deflection beam shape reconstruction based on a beam model incorporating Poisson effect and is thus able to take into account bending, torsion, shearing and tensile-compression deformations. Exemple of application on circular beams is conducted with beam shape reconstructed from FEM simulations strain measures. Results show that, compared to beam shape sensing methods using axial strain, the beam shape method proposed provides a significant increase in the reconstruction accuracy when the beam is subject to deformations containing torsion.
       
  • Best non-polynomial shear deformation theories for cross-ply single skin
           and sandwich shells
    • Abstract: Publication date: Available online 23 November 2019Source: Engineering StructuresAuthor(s): J.C. Monge, J.L. MantariAbstractThis paper presents Best Theory Diagrams (BTDs) constructed from non-polynomial terms to identify best shell theories for bending analysis of cross-ply single skin and sandwich shell panels. This structure presents a constant radii of curvature. The shell theories are constructed using Axiomatic/Asymptotic Method (AAM). The different shell theories are described using the Carrera’s Unified Formulation. The governing equations are derived from the Principle of Virtual Displacement (PVD). Navier-Type closed form solution is used for solving the bending problem of simply supported doubly curved shell panels subjected to bi-sinusoidal transverse pressure. The BTDs built from non-polynomial functions are compared with Maclaurin expansions. Spherical shell panels with different layer-configurations are investigated. The results demonstrated that the shell models obtained from the BTD using non-polynomial terms can improve the accuracy obtained from Maclaurin expansion for a given number of unknown variables of a displacement field.
       
  • A practical methodology for optimum seismic design of RC frames for
           minimum damage and life-cycle cost
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): Payam Asadi, Iman HajirasoulihaAbstractThe design criteria in current seismic design codes are mainly to control lateral displacements and provide adequate strength to sustain expected design load combinations. However, to achieve the most economic design solutions, the life-cycle total cost (TLCC), which includes both initial structural cost and expected damage cost, should be also considered for the probable earthquakes during the lifetime of the structure. In the present study, the TLCC of the buildings is used as the main objective function for optimum seismic design of reinforced concrete (RC) frames. First, it is demonstrated that the blind increase of the reinforcement ratios does not necessarily reduce the displacement demands and the damage costs. Subsequently, a practical methodology is developed for the optimum seismic design of RC frames based on the concept of uniform damage distribution (UDD). Using an adaptive iterative procedure, the distribution of inter-storey drifts and TLCC of the floors is modified along the height of the structure. To demonstrate the efficiency of the method, 5, 8 and 12 storey RC frames are optimized using the proposed algorithm. The results indicate that, while all predefined performance targets are satisfied, the maximum inter-storey drift ratio and TLCC of the frames are considerably reduced (up to 56% and 45%, respectively) only after a few steps. The proposed method should prove useful for more efficient performance-based design of RC frames in practice.
       
  • Hysteretic behavior of multi-cell L-shaped concrete-filled steel tubular
           columns at different loading angles
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): Yongqian Zheng, Shaokun Yang, Pengsong LaiAbstractMulti-cell L-shaped concrete-filled steel tubular (CFST) columns have the advantages of avoiding column protrusion, saving room space and good mechanical behavior. They can be used as the corner columns in building structures. In practical engineering, the columns may be subjected to earthquake action from different directions. However, there are few experimental and numerical studies on this kind of columns at different loading angles. This paper presents four tests carried out on multi-cell L-shaped CFST columns subjected to combined constant compression and lateral cyclic loads. The main variables were loading angles (0°, 45° and 135°) and axial load levels (0.25 and 0.5). The failure modes, lateral load – displacement hysteretic curves, envelope curves, stiffness degradation, ductility, energy dissipation, deformation and moment – curvature curves were obtained. A finite element model was developed to simulate the multi-cell L-shaped CFST columns at different loading angles, and the predicted results agreed well with the test results. Moreover, the parametric analysis was conducted to investigate the effects of various parameters on lateral load – displacement curves of the columns under diagonal loading.
       
  • Behaviour and residual compression resistances of circular high strength
           concrete-filled stainless steel tube (HCFSST) stub columns after exposure
           to fire
    • Abstract: Publication date: Available online 22 November 2019Source: Engineering StructuresAuthor(s): An He, Yating Liang, Ou ZhaoAbstractThe structural behaviour and residual compression resistances of circular high strength concrete-filled stainless steel tube (HCFSST) stub columns after exposure to fire were experimentally and numerically investigated in this paper. The experimental study was performed on 12 circular HCFSST stub column specimens after exposure to the ISO-834 standard fire for three levels of heating durations (15 min, 30 min and 45 min) as well as 4 unheated circular HCFSST stub column specimens (i.e. reference specimens). The experimental study was supplemented by a numerical modelling study, where two types of finite element (FE) models, namely heat transfer and mechanical FE models, were firstly developed to simulate the thermal and mechanical responses of the circular HCFSST stub column specimens, and then used to perform parametric studies to derive additional numerical results. Due to the lack of existing design codes for concrete-filled stainless steel tube members and concrete-filled carbon steel tube members after exposure to fire, the corresponding codified design provisions for circular concrete-filled carbon steel tube members at room temperature, as established in Europe, Australia and America, were evaluated for their suitability to circular HCFSST stub columns after exposure to fire, based on the test and numerical parametric study results. It was generally found that both the European and Australian codes yield a high level of accuracy and consistency in predicting the residual compression resistances of circular HCFSST stub columns after exposure to fire, while the American specification leads to rather conservative and scattered design residual compression resistances.
       
  • Inelastic lateral buckling of steel cantilevers
    • Abstract: Publication date: Available online 22 November 2019Source: Engineering StructuresAuthor(s): N.S. TrahairAbstractSteel cantilevers are very different from the simply supported beams under uniform bending which provide the basis for designing steel members against lateral buckling. Cantilevers have different end restraint conditions, while the most critical loading condition for cantilevers is one of concentrated end load leading to a linear moment distribution. Thus the elastic lateral buckling formulations for uniform bending of simply supported beams used more generally for design are inappropriate for cantilevers.The mono-symmetric yield patterns in simply supported beams with residual stresses in uniform bending are of opposite sense to those of cantilevers because of the opposite sense of the bending moments. Thus formulations which take account of the effect of mono-symmetry on the inelastic lateral buckling of simply supported beams are inappropriate for cantilevers. Further, the linear cantilever moment distribution leads to very localised yielding instead of the uniform yielding of beams under uniform bending.This paper studies the inelastic lateral buckling of cantilevers in order to produce better design guidance than that currently based on the inelastic buckling of simply supported beams in uniform bending. The effects of mono-symmetry on the elastic buckling of beams and cantilevers are first investigated, and then the effects of the mono-symmetric non-uniform yielding patterns which complicate the prediction of the inelastic buckling resistances of cantilevers are studied. Cantilevers with reduced (instead of rigid) end warping restraints occur in overhanging beams, and so the effects of yielding on overhanging segments are also studied.These studies are used to develop simple approximate methods for designing cantilevers and overhanging segments against inelastic lateral buckling.
       
  • Characterization of debris throw from masonry wall sections subjected to
           blast
    • Abstract: Publication date: Available online 21 November 2019Source: Engineering StructuresAuthor(s): J.M. Schneider, M. von Ramin, A. Stottmeister, A. StolzAbstractThe failure of structural components, e.g. masonry walls, due to accidental or intentional explosions exhibits a considerable risk to the health of persons, operational safety, and surrounding structures. The debris throw originating from overloaded structural elements poses a significant threat to structures and persons in the surrounding environment in distances, which may exceed the hazard-range of the blast wave itself. Insights into the break-up process during structural failure and the resultant debris throw characteristics expressed in terms of fragment mass distributions, initial velocities and launch angles, are thus essential to assess the significant potential explosion hazard. However, to date the data basis for hazard assessment and model development on debris throw of masonry structures is limited. In this article, we present the results from shock-tube experiments of single-span masonry walls subjected to dynamic blast loads characteristic for far-field explosions and free-field blast propagation. Reflected peak overpressures in the tests ranged from 100 to 150 kPa with corresponding maximum impulses of approximately 2000 kPa ms to 3000 kPa ms. A new methodology based on high-speed stereo video imaging allows to analyze the break up process and the resulting debris sizes, launch velocities and three-dimensional launch angles before the debris hit the ground. The data derived can be used for empirical predictions of debris launch characteristics as well as for the validation of numerical simulations aimed at the proper assessment of hazardous secondary blast effects from masonry failure.
       
  • Nonlinear dynamic analysis method for large-scale single-layer lattice
           domes with uncertain-but-bounded parameters
    • Abstract: Publication date: Available online 21 November 2019Source: Engineering StructuresAuthor(s): Huidong Zhang, Xinqun Zhu, Shu YaoAbstractCurrently, nonlinear dynamic analysis for large-scale single-layer domes is commonly performed using deterministic numerical methods. However, in practical engineering cases, complex large-scale single-layer domes have many uncertain parameters that cannot be considered using deterministic methods. Therefore, there is a growing awareness that classical deterministic methods need to be extended towards the introduction of the uncertain aspects in dynamic analysis, and a non-deterministic analysis method for large-scale spatial structures is required. In this paper, a new method is presented by introducing uncertainties into the nonlinear dynamic analysis for large-scale single-layer lattice domes. The method accounts for uncertainties in material properties, structural imperfections, loads, and damping with bounds. The focus is on the treatment of uncertainty in damping and the adopted geometric shape, which is different from that of conventional approaches. Finite element dynamic analyses for sample structures with multiple sources of uncertainty subjected to dynamic loads are performed. Results show that the variability of the variables with an associated uncertainty imposes significant negative effects on the dynamic properties, dynamic demands, and safety of a dome. Uncertain damping in a structure plays the most important role in determining structural performance. The numerical results reveal the differences between conventional analysis methods with deterministic parameters used in previous practical applications and the uncertain analysis method. Finally, a parametric study is performed, and the impacts of sample size on statistical dynamic demands, single uncertain source on structural failure, and single uncertain source on damping coefficients are discussed.
       
  • Initial stiffness of self-centering systems and application to
           self-centering-beam moment-frames
    • Abstract: Publication date: Available online 21 November 2019Source: Engineering StructuresAuthor(s): Xiaogang Huang, Matthew R. Eatherton, Zhen ZhouAbstractThere has been considerable development of self-centering seismic force resisting systems in the past few decades, many of which incorporate gap opening mechanisms. Experiments on these self-centering systems often result in an initial stiffness that is less than the predicted theoretical stiffness. While the discrepancy has often been attributed to uneven bearing surfaces at the gap opening mechanism, the cause of the low stiffness is not well understood and can have critical importance for drift-controlled systems such as moment frames.Concepts related to the initial stiffness of self-centering systems are investigated and the difference between experimental and theoretical initial stiffness is evaluated for a range of previous testing programs on different types of self-centering systems. Seven sources of added flexibility are identified. Then, the concepts for improving initial stiffness are applied to one specific system, the self-centering beam moment frame (SCB-MF). The self-centering beam consists of a two-part beam (upper and lower parts), post-tensioning strands to keep the parts aligned, and bolted friction elements to dissipate seismic energy. The initial stiffness of the SCB-MF is predicted using derived equations and finite element analyses and then the predictions are evaluated against experimental results. It is shown that if the added sources of flexibility are neglected (which is typical practice), the ratio of the average initial secant stiffness from five experiments to the predicted value is 38%, but that if the sources of flexibility are considered, the initial stiffness can be captured. The average ratio of measured to predicted stiffness for the theoretical model including pin flexibility is 59%, while the average ratio for finite element analyses including pin flexibility and beam length tolerance is 102%, demonstrating a significant improvement in accuracy. Using this new understanding about the sources of flexibility in self-centering systems, methods for increasing the stiffness of the SCB-MF are proposed and evaluated.
       
  • Experimental investigation of a timber-concrete floor panel system with a
           hybrid glass fibre reinforced polymer-timber corrugated core
    • Abstract: Publication date: Available online 21 November 2019Source: Engineering StructuresAuthor(s): Ya Ou, Joseph M. Gattas, Dilum Fernando, José L. ToreroAbstractHybrid timber-concrete (HTC) floor systems are well-suited for prefabricated construction and so have seen widespread use in modern sustainable buildings. This paper investigates a novel extension to such systems by introducing a corrugated core between tensile timber and compressive concrete layers. This new ‘HTCC’ floor panel system is hypothesised to have an increased weight-specific flexural capacity relative to HTC systems, by reducing the volume of concrete below the panel neutral axis without decreasing flexural capacity. This paper experimentally investigates the flexural performance of the new system, acting in two configurations: with core orientation parallel to the span for maximum longitudinal one-way spanning capacity; and with core orientation transverse to the span for generation of a novel transverse spanning capacity. In total, eight HTCC floor panels were prepared and tested, with the flexural capacities and critical failure modes analysed for each. Effects of different core geometries, shear force transfer methods, and manifested composite action are also closely studied. Longitudinal specimens achieved the best composite action and correspondingly the highest panel performance, with a 73% ultimate moment carrying efficiency and an 85% stiffness efficiency at SLS, compared to an idealised HTC section with full composite action.
       
  • Procedure for parameter identification and mechanical properties
           assessment of CLT connections
    • Abstract: Publication date: Available online 16 November 2019Source: Engineering StructuresAuthor(s): Jixing Cao, Haibei Xiong, Lin ChenAbstractConnections in cross-laminated timber (CLT) structures are crucial components that can affect the behaviour of the whole structure. A novel framework that integrates the unscented Kalman filter (UKF) as an estimation tool with a hysteretic model is developed to identify the model parameters of a nonlinear system. The UKF estimates the mean and covariance of the model parameters using unscented transformation (UT) by a set of deterministically chosen sample points. The proposed framework is applied to identify the unknown model parameters of CLT connections using available experimental data, where the cycle behaviour of CLT connections is simulated using a spring element assigned to the hysteretic model. The comparison of hysteretic curves between the test and model shows that the results identified with UKF are precise. Two different approaches are proposed: an assessment according to the EN 12512 standard, and a damage accumulation assessment. The EN 12512 standard assessment is evaluated from the elastic stiffness, ductility ratio, and energy dissipation, whereas the damage accumulation assessment considers the effects of low amplitude and accumulated damage. Together, these two methods fully evaluate the identified result and the mechanical characteristics of CLT connections. The proposed procedure of parameter identification using the UKF (together with the mechanical properties assessment) can be applied to other connections in timber engineering.
       
  • Transverse reinforcement optimization of a precast special roof element
           through an experimental and numerical procedure
    • Abstract: Publication date: Available online 15 November 2019Source: Engineering StructuresAuthor(s): Patrizia Bernardi, Roberto Cerioni, Elena Michelini, Alice SiricoAbstractThe transverse behavior of a long span three-plate precast roof element is investigated by means of an experimental and numerical research. The performed study highlights that the failure mode of this folded-plate element is strongly influenced by the amount of transverse reinforcement in the wings. This latter is usually designed through simplified methods, which often lead to over-dimensioning in terms of steel welded mesh. To avoid excessive costs for the producers, transverse reinforcement optimization should be required. In this work, a non-linear FE modelling was applied for this purpose. The reliability of the followed numerical procedure was first verified by an initial type testing (i.e. experimental load test up to failure). The agreement between numerical and experimental results showed the efficiency of the model in simulating all the main sources of non-linearity related to both material behavior and element geometry. Numerical analyses were so used to perform a parametric study as a function of transverse reinforcement amount, aimed at determining a coefficient of “model inaccuracy”. This coefficient should be used as a correction factor for the element design in routine calculations based on beam theory.
       
  • Nonlinear analysis of compact and thin-walled metallic structures
           including localized plasticity under contact conditions
    • Abstract: Publication date: Available online 15 November 2019Source: Engineering StructuresAuthor(s): M.H. Nagaraj, I. Kaleel, E. Carrera, M. PetroloAbstractThis work presents the numerical analysis of elastoplastic contact problems of compact and thin-walled metallic structures. The emphasis is on the use of higher-order 1D elements with pure displacement variables and based on the Carrera Unified Formulation (CUF) to capture localized effects and cross-sectional distortions. Contact interactions are normal and frictionless via a node-to-node contact algorithm with the penalty approach for contact enforcement. The analysis considers the material nonlinearity via the von Mises constitutive law. Numerical assessments compare the CUF solutions with 3D finite element analysis concerning the solution quality, computational size, and analysis time. The results show the ability of 1D CUF models of accurately evaluating localized deformations and plasticity. The CUF results are in good agreement with reference 3D finite element solutions, and require an order of magnitude fewer degrees of freedom and analysis time, making them computationally efficient.
       
  • Updated evaluation metrics for optimal intensity measure selection in
           probabilistic seismic demand models
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): Farid Khosravikia, Patricia ClaytonAbstractThis study proposes an update on the criteria that are typically used to select the optimal intensity measures (IMs) for development of probabilistic seismic demand models (PSDMs), which relate the input seismic hazard and structural responses. Employing an optimal IM contributes to decreasing the uncertainty in the PSDMs, which, in turn, increases the reliability of the PSDMs used in performance-based earthquake engineering analyses. In the literature, the optimality of the IMs is generally evaluated by the following metrics: efficiency; practicality; proficiency, which is the composite of efficiency and practicality; sufficiency; and hazard computability. The present study shows that the current criteria for evaluating the practicality and proficiency features may mislead the selection of the optimal IM when IMs with different ranges and magnitudes are investigated. Moreover, the efficiency metric can provide biased results when comparing IMs for predicting demands of different structural components or types of systems. As a result, alternative solutions are proposed to investigate the efficiency, practicality, and proficiency features of the IMs. The suggested metrics are employed in a case study to evaluate the IMs used to develop PSDMs for multi-span continuous steel girder bridges in Texas subjected to human-induced seismic hazard.
       
  • Behavior of lightly reinforced fiber reinforced concrete panels under pure
           shear loading
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): Luca Facconi, Fausto MinelliAbstractThe load-deformation response of Fiber Reinforced Concrete (FRC) elements subjected to pure shear is still matter of strong debate within the scientific community. In this paper, the tests on six fiber reinforced concrete panels under pure shear are presented and discussed. The tests were conducted under displacement control and a peculiar loading frame was designed to ensure that a pure shear state of stress was established. Steel fibers were added in relatively low amounts (20 and 50 kg/m3), and two steel reinforcements (0.21% and 0.74%) were selected, aiming at simulating lightly reinforced elements. A critical discussion on the influence of fibers on both global and local behavior (tension stiffening, cracking formation and propagation, post-cracking stiffness and residual strength) is presented. Finally, a novel crack spacing formulation, extended to FRC, is proposed and compared against available experimental data.
       
  • Simulation and design of semi-compact elliptical hollow sections
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): Xin Meng, Leroy GardnerAbstractCurrent structural steel design codes typically feature a step in the cross-sectional resistance functions at the Class 2 slenderness limit due to the abrupt switch between elastic and fully plastic capacities. To address this issue, new design rules, featuring a gradual transition between elastic and plastic resistances, have been recently developed for semi-compact (Class 3) I- and box sections to account for the partial spread of plasticity. This approach is extended herein to the cross-section and member buckling design of semi-compact elliptical hollow sections (EHS). Finite element models were first established and validated against previous test results; particular attention was given to the modelling of local geometric imperfections. Parametric studies were then conducted, where over 4000 structural performance data were numerically generated covering a wide range of cross-section aspect ratios, material properties, local and global slendernesses and load combinations. Upon completion of the numerical simulation programme, structural design rules of semi-compact EHS were developed. The classification of EHS under biaxial bending and compression plus biaxial bending was initially addressed. Following this, new design expressions featuring elasto-plastic section properties were developed to exploit partial plastification at both cross-section and member buckling levels. The accuracy of the design proposals was evaluated through comparisons between the test/numerical data and the resistance predictions; the comparisons revealed that the proposed elasto-plastic cross-section and member buckling design rules lead to both improved accuracy and consistency over the existing elastic provisions. The reliability of the proposals was verified through statistical analyses in accordance with EN 1990, demonstrating their suitability for incorporation into the next revision to EN 1993-1-1.
       
  • Shear behavior of novel hybrid composite beams made of self-consolidating
           concrete and engineered cementitious composites
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): K.M.A. Hossain, S. Hasib, T. ManzurAbstractShear performances of hybrid composite beams, a combination of two different layers of self-consolidating concrete (SCC) and engineered cementitious composites (ECC) were investigated. Composite beams were made with two different ECC to SCC depth ratios. Full depth beams, consisting of a single layer of either SCC or ECC, were also made and tested to compare their performance with respect to that of hybrid composite beams. Both full depth and composite beams were made with and without shear reinforcement. The performance of shear beams was evaluated in terms of load-deflection response, first diagonal crack load, post-cracking shear resistance, energy absorption, and ductility index. Compared to the full depth SCC and full depth ECC beams, non-shear reinforced hybrid composite beams showed higher ductility and energy absorption capacity which indicates suitability of hybrid composite to be used in earthquake resisting elements. Hybrid composite beams also showed higher number of cracks with lower crack width. Code based equations and other design specifications were found to be conservative in predicting shear strength of hybrid composite beams. However, the theoretical capacity was found to be higher than that of experimental shear resistance in case of full depth ECC beams.
       
  • Probabilistic evaluation of earthquake-induced sloshing wave height in
           above-ground liquid storage tanks
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): R.J. Merino, E. Brunesi, R. NascimbeneAbstractPast earthquakes have repeatedly demonstrated the need to properly design above-ground liquid storage tanks to mitigate their potential for damage due to seismic actions. One important damage mechanism in these plant items is the height of the sloshing wave exceeding the freeboard height provided to the tank. This paper proposes and presents a probabilistic framework to evaluate risk-oriented safety factors that can aid in the design of the freeboard height. The procedure is based on a series of dynamic analyses performed over a tank portfolio. The process accounts for record-to-record variability by using a set of 50 historical ground motion records, while it accounts for the variability in the geometric properties of tank prototypes by generating a random population of 100 cylindrical tanks through Monte Carlo simulation. The randomly generated tank properties are used to develop a simple mechanics-based model for each simulated tank, which is then subjected to the 50 ground motion records scaled to three seismic intensities by using two record scaling strategies. The trends in the resulting sloshing wave height values in relation to the randomly generated tank geometric properties are thoroughly analyzed and discussed, indicating that large and squat tank archetypes are particularly sensitive to sloshing. Finally, two sets of risk-oriented safety factors are developed by comparing the results of the set of dynamic simulations with those computed by using the prescriptions given by American standards.
       
  • Thrust Surface Method: An innovative approach for the three-dimensional
           lower bound Limit Analysis of masonry vaults
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): Aguinaldo Fraddosio, Nicola Lepore, Mario Daniele PiccioniAbstractWe propose a new computational equilibrium approach for the structural safety assessment of historical masonry vaults of any geometry under general loading conditions. This approach, called Thrust Surface Method (TSM), represents an innovative application of the lower bound theorem of Limit Analysis to masonry vaults modeled as continuous No-Tension bodies. In particular, on allowing for singular stresses, the search of statically admissible stress field is reduced to the search of purely compressed membranes in equilibrium with the applied loads and entirely contained into the thickness of the vault. Based on a convenient numerical procedure and the formulation of a suitable constrained optimization problem, TSM is a method of practical application that, looking for “extremal” or “optimal” solutions, is capable of fully exploring the entire load-bearing capacity spectrum of a vault having an arbitrary geometry. Since the particular formulation, TSM can take into account not only any kind of vertical loads, but also horizontal loads like those simulating the maxima inertia effects related to seismic actions. In addition, the proposed approach could be a useful tool for visualizing and understanding the complex three-dimensional behavior and the close relationship between form and structure characterizing masonry vaults.The effectiveness and the capabilities of the method are discussed in light of some representative case studies, allowing for suitable comparisons with the results of other analytical and experimental approaches in the literature.
       
  • Robustness quantification of reinforced concrete structures subjected to
           progressive collapse via the probability density evolution method
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): De-Cheng Feng, Si-Cong Xie, Jun Xu, Kai QianAbstractRobustness is the most comprehensive and acceptable index that describes the ability of structures to withstand progressive collapse induced by accidental extreme events such as impact, explosion and terrorist attacks. As found in the literature, several approaches have been proposed to quantify the robustness of a structure, e.g., approaches based on deterministic structural performance, failure probabilities (or the collapse reliabilities), and collapse risks. In this paper, the reliability-based approach is adopted to quantify the structural robustness of reinforced concrete (RC) structures subjected to progressive collapse since it is a trade-off between comprehensiveness and operability. An efficient calculation framework is developed based on the probability density evolution method (PDEM). Emphasis is placed on two aspects, i.e., the progressive collapse behavior modeling and the evaluation of the structural reliability. The static nonlinear pushdown method is employed to represent the progressive collapse capacity of the structures, and the force-based frame element is used to generate the finite element model. Then, the PDEM incorporated with the equivalent extreme value event is used to capture the reliability indices before and after progressive collapse. With the reliability indices, the robustness index can be easily computed. The developed framework is applied to two prototype RC frames designed in accordance with the Chinese design code. The reliability and robustness indices of the frames under different initial local damage scenarios (namely, removal of columns in typical pushdown method) are obtained, and the influences of the position of the initial damage scenarios on the robustness are also discussed.
       
  • Modelling unsteady self-excited wind force on slender prisms in a
           turbulent flow
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): Zengshun Chen, K.T. Tse, K.C.S. Kwok, Bubryur Kim, Ahsan KareemAbstractA mathematical model to quantify the unsteady self-excited forces (USEFs) acting on a slender prism was developed, to address the shortcomings of the classical quasi-steady theory employed to predict the galloping instability of slender prisms. The unsteady aerodynamic force and galloping response of a prism were measured from a hybrid aeroelastic-pressure balance (HAPB) that can synchronously observe unsteady pressure and aeroelastic response. It was found that the galloping response predicted by the unsteady aerodynamic force is in close agreement with the experimental result whereas the quasi-steady theory cannot predict the galloping instability. According to an energy equivalent method, the unsteady aerodynamic force was quantitatively decomposed into three components: an aerodynamic damping force component, an aerodynamic stiffness force component and a residual force (buffeting force) component. Subsequently, a nonlinear mathematical model for the USEF which is a 1st-order polynomial function representing the aerodynamic damping and stiffness force components, was established. The results indicated that the 1st-order model was effective in predicting the galloping response of the prism. It was also demonstrated that the model can be used to predict the galloping instability of prisms with different mass-damping ratios.
       
  • Comprehensive analysis of Fiber Reinforced Concrete beams with
           conventional reinforcement
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): Paula Folino, Marianela Ripani, Hernán Xargay, Nicolás RoccaAbstractThe aim of this work is to analyze the failure and mechanical behavior of full-scale reinforced concrete beams elaborated with fiber reinforced concrete. Although several researches can be found in the literature related with the study of the mechanical behavior of fiber reinforced concrete, only few of them are related to real-scale structural elements. With the purpose of characterizing the material, in the first part of the paper experimental results corresponding to compressive tests and splitting tensile tests on cylindrical specimens, as well as three point bending tests on small notched beams considering plain and fiber reinforced concrete are addressed. Then, experimental results corresponding to four point bending tests on real-scale reinforced concrete beams, including different contents of industrial steel fibers in conjunction with different conventional reinforcement layouts, are presented and discussed. As expected, it was observed that fibers contribute to enhance structural integrity in post-peak behavior, both in small and structural elements. It was also observed that although the addition of fibers caused an increase in tensile strength on small samples, no evident differences were detected among cracking load values of full-scale beams with different fiber contents under bending. The evolution of crack widths with increasing loads was measured and analyzed in the experimental campaign in this work. In the last part of the paper, experimental results corresponding to ultimate bending and shear loads were compared with numerical estimations proposed in available international recommendations for structural design. It was detected that for the considered materials, current recommendations seem to be not enough conservative for predicting bending strength, contrary to the case of shear strength, where higher residual strengths were evidenced.
       
  • Seismic performance of innovative hybrid precast reinforced concrete
           beam-to-column connections
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): Haider Hamad Ghayeb, Hashim Abdul Razak, N.H. Ramli SulongAbstractPrecast construction of structural buildings requires connection techniques that can shorten the process using only simple on-site activities while still guaranteeing adequate strength, energy dissipation, stiffness, and ductility. The construction methods should decrease the use of formwork and temporary bracing to save time and costs. In this study, innovative hybrid connections using steel tubes, steel plates, and steel couplers to join beams and columns were proposed and tested under reversed cyclic loading. Five half-scale samples of the hybrid precast joints, including the monolithic and precast joints, were examined to evaluate the seismic performance of the connections. The hybrid connections showed better performance in terms of load, displacement, drift ratio, ductility, strength, stiffness, and energy dissipation compared to a monolithic connection. The drift ratio, moment capacity, strength, and total cumulative energy dissipation of the hybrid connections were higher by 12.5–50.0%, 34.68–59.57%, 35.0–60.0%, and 50.99–331.32%, respectively, when compared with a monolithic connection. The failure modes of the hybrid connections were governed by yielding steel reinforcement, yielding steel plate, and flexural failure, with less extensive damage compared to the monolithic joint. The hybrid connections were effective in shifting the plastic hinges to outside the connection zone. Therefore, the hybrid connections can be used in high seismic zones because the superior performance results meet the requirements of the seismic codes.
       
  • Experimental study of isolation in the backfill zone of the foundation pit
           (IBF) method to reduce ground-borne vibration in buildings
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): Yi Zeng, Peng Pan, Dongbin Zhang, Jun YangAbstractStructural vibration caused by road traffic disturb the comfort of people in nearby buildings and induce various public health hazards Isolation trenches can reduce vibration but are often not practical in large cities. This paper proposes the isolation in the backfill zone of the foundation pit (IBF) method to reduce the building vibration using the existing construction backfill zone. A new isolation product, which has high axial stiffness and low shear stiffness, was developed. The IBF method, which employed the product, can restrain the building foundation and provide good vibration isolation. A method for designing the high axial stiffness and low shear stiffness (HALS) vibration isolation product was also proposed. Two four-story test buildings were constructed and full-scale on-site tests were conducted. The vibration transmitted through the basement sidewalls was measured and the effectiveness of the IBF method was investigated. It was observed that the IBF method can reduce 31–53% of the vibration transmitted to the building.
       
  • Drying shrinkage model for recycled aggregate concrete accounting for the
           influence of parent concrete
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): Qinghe Wang, Yue Geng, Yuyin Wang, Huan ZhangAbstractThe drying shrinkage of recycled aggregate concrete (RAC) varies considerably owing to the extensive sources of parent concrete from which recycled aggregates are obtained. This paper proposes a theoretical drying shrinkage model for RAC considering the properties of the parent concrete, including its service time and strength. To achieve this, shrinkage tests were conducted on 60 concrete specimens over 360 days. Five types of parent concrete with different service times (1 year, 20 years, and 42 years) and water-to-cement ratios (0.30, 0.45, and 0.60) were crushed to obtain recycled coarse aggregates (RCAs) that were used to prepare the RAC specimens. Three RCA replacement ratios (0%, 50%, and 100%) and three RAC water-to-cement ratios (0.30, 0.45, and 0.60) were assessed. The results indicated that the drying shrinkage of RAC was effectively reduced by an increase in the parent concrete strengths and vice versa. A theoretical RAC shrinkage model was developed considering the influence of the residual mortar content and parent concrete strength. A benchmarking analysis using 262 shrinkage samples demonstrated that the proposed model offers improved accuracy for estimating the long-term drying shrinkage of RAC over existing methods, particularly when the parent concrete and RAC have large strength variations.
       
  • Evaluation of optimal sensor placement algorithms for the Structural
           Health Monitoring of architectural heritage. Application to the Monastery
           of San Jerónimo de Buenavista (Seville, Spain)
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): Pablo Pachón, María Infantes, Margarita Cámara, Víctor Compán, Enrique García-Macías, Michael I. Friswell, Rafael Castro-TrigueroAbstractIn recent years, Structural Health Monitoring (SHM) based on Operational Modal Analysis (OMA) and damage detection tools has become a popular non-destructive solution to assess the real-time integrity of any kind of structure. This technique is especially well-suited for the condition-based conservation of historical structures, where minimal invasiveness must be ensured owing to their high cultural and architectural value. Optimal Sensor Placement (OSP) techniques represent a valuable tool for efficiently designing the sensor layout in a SHM system in order to achieve an effective modal identification with a reduced number of sensors and, consequently, an improved cost efficiency. In this light, this paper proposes a design methodology of sensor networks based on OSP techniques suitable for historical structures. To do so, a preliminary extensive OMA campaign is conducted in order to construct a reliable finite element (FE) model by fitting the identified modal properties. Afterwards, an optimal sensor arrangement with a limited number of sensors is obtained by applying different model-based OSP techniques. In order to improve the robustness of the solution, material uncertainties are included in the model and the optimal sensor placement is conducted within a statistical framework. This methodology is presented and evaluated with a case study of a Spanish secular building: the Monastery of San Jerónimo de Buenavista in Seville (Spain). In particular, this paper presents the results of the preliminary ambient vibration test and the modal identification of the monastery, the updating process of the FE model, as well as a critical review of the different OSP techniques within a framework of material parameter uncertainty. The presented analysis demonstrate that OSP techniques based on the rank optimization of the kinetic energy matrix of the structure yield robust sensor layout.
       
  • Experimental and numerical investigation of low-yield-strength (LYS) steel
           plate shear walls under cyclic loading
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Mojtaba Gorji Azandariani, Majid Gholhaki, Mohammad Ali KafiAbstractSteel plate shear walls (SPSWs) are lateral load resisting systems with a significant energy dissipation potential under cyclic loading. This research performed experimental and numerical investigation of the cyclic behavior of low-yield-strength (LYS) SPSW. Two specimens with 1:3 scale three-story single-bay SPSW with unstiffened infill plates were tested using cyclic loading. The steel plate shear walls had two types of moment-resistant and pinned beam-to-column connections. Also, low-yield-strength (LYS) and high-yield-strength (HYS) steel were used for the infill plates and boundary frames, respectively. The results indicated that the test specimens had good stiffness, high ductility, significant energy dissipation, and stable cyclic behavior. Also, the results revealed that the type of beam-to-column connection affects ductility, strength, and energy dissipation and has a negligible effect on the initial stiffness. In addition, the nonlinear finite element (FE) models were developed to predict the hysteresis behavior of SPSWs. In the FE models, the nonlinear behavior of geometric and materials, large deformations, and initial geometric imperfections were considered. The nonlinear FE models of SPSWs were verified against experimental results. The hysteresis curves, failure modes, and base shear capacity FE models were compared with the experimental results. The numerical investigation showed that the cyclic behavior of the SPSW could be simulated using a simplified FE model. It is demonstrated that rigid and pinned beam-column connection can influence the strength performance and total energy dissipation of an SPSW system and material properties of the infill plate components, especially LYS steel, can further advance the impact of such connection.
       
  • Seismic performance of predamaged RC columns strengthened with HPFL and
           BSP under combined loadings
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Hua Huang, Min Huang, Wei Zhang, Mengxue Guo, Stanislav PospisilThis paper presents an experimental investigation of the seismic behavior of coupling predamaged reinforced concrete (RC) columns strengthened with high-performance ferrocement laminate (HPFL) and bond steel plate (BSP) that are subjected to combined loadings. A total of four specimens were fabricated. After they were predamaged with corrosion and an earthquake environment, they were strengthened with HPFL and BSP, and then tested under four different combined loadings, separately, which are unidirectional compression, bending, and shear (CBS); bidirectional CBS; unidirectional compression, bending, shear, and torsion (CBST); and bidirectional CBST. Their seismic behavior, including failure mode, bearing capacity, ductility, energy dissipation, stiffness degradation, damage index and residual displacement, was analyzed. The results revealed that the coupling predamaged RC columns still had retrofit value and that the retrofitting method utilized in this paper was effective. After repairing with HPFL and BSP, the bearing capacity can be significantly improved especially for torsional specimens, which increased by more than 100%. Other seismic behavior like ductility coefficient, stiffness, and single cyclic energy dissipation can be recovered well. In addition, the horizontal eccentricity had a negative effect on the seismic behavior of specimens, while the negative effect was reduced after strengthening.Graphical abstractCorrosion-post strengthened RC columns subjected combined loadings.Graphical abstract for this article
       
  • Local stability of press-braked stainless steel angle and channel
           sections: Testing, numerical modelling and design analysis
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Lulu Zhang, Kang Hai Tan, Ou ZhaoAbstractThis paper reports an experimental and numerical investigation into the local stability of press-braked stainless steel angle and channel sections. The experimental programme was performed on two equal-leg angle sections and two plain channel sections, and included material testing, initial local geometric imperfection measurements, eight stub column tests and ten laterally restrained beam tests (about the geometric axes for angle sections and minor principal axes for channel sections). This was supplemented by a numerical simulation programme, where finite element models were firstly established to replicate the test structural responses and then employed to derive further numerical data through parametric studies. The results obtained from the structural testing and numerical modelling were adopted to evaluate the accuracy of the codified local buckling design provisions established in America, Europe and Australia and New Zealand. The evaluation results revealed that all the design codes greatly underestimate the cross-section resistances of press-braked stainless steel equal-leg angle and plain channel section stub columns and laterally restrained beams, mainly attributed to the neglect of the pronounced material strain hardening effect of stainless steel in the design. The continuous strength method (CSM) is an advanced deformation-based design method, allowing for a rational utilisation of material strain hardening in determining cross-section resistances, and its scope of application has been recently extended from doubly-symmetric (I- and tubular) sections to mono-symmetric and asymmetric (angle, channel and T-) sections. Quantitative evaluation of the CSM was conducted through comparing the predicted cross-section resistances against the experimental and numerical results. The CSM was found to yield substantially more accurate and consistent design cross-section resistances for press-braked stainless steel equal-leg angle and plain channel section stub columns and laterally restrained beams than the established design codes.
       
  • Propagation and quantification of uncertainty in the vulnerability
           estimation of tall concrete bridges
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): Farahnaz SoleimaniAbstractBridges are critical links in a transportation network, and their seismic vulnerability can lead to substantial economic losses, particularly the ones located in high-risk seismic zones. Bridge vulnerability can be assessed by developing fragility curves that indicate the probability of reaching or exceeding a specific level of damage. Past earthquakes have revealed a high likelihood to experience seismic damage for bridges with irregularities in their configurations. Since the research on the seismic reliability of irregular bridges with consideration of uncertainty is limited, this paper aims to address this deficiency by analyzing the impacts of typical sources of uncertainties including ground motion, material, and geometric attributes on the vulnerability of tall and normal box-girder concrete bridges. This study compares the fragility of considered cases by performing nonlinear time history analysis of representative bridges and developing probabilistic seismic demand models in order to generate the corresponding fragility curves. During this process, the influence of each type of uncertainty is investigated through statistical analysis of the bridge responses. The findings demonstrate a noticeable seismic risk of tall bridges compared to the normal ones, and among the evaluated categories, the uncertainties associated with the geometric attributes showed the highest influence on the seismic demands.
       
  • A stress-path dependent stress-strain model for FRP-confined concrete
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): M.H. Lai, Y.W. Liang, Q. Wang, F.M. Ren, M.T. Chen, J.C.M. HoAbstractHigh-strength concrete (HSC) has higher strength-to-weight ratio and stiffness than normal-strength concrete (NSC). Therefore, the use of HSC can decrease the construction and demolition waste and embodied carbon content of structural members that enhances the urban sustainability. However, HSC is more brittle than NSC. To further push up the maximum concrete strength limit in practical construction, confining concrete by fibre-reinforced polymer (FRP) has been advocated to restore ductility. Compared with using hollow-steel tube as confinement, FRP has lighter weight, higher tensile strength, better corrosion resistance, and is more durable and flexible. Nevertheless, it is up to now a difficult task to predict accurately the uni-axial stress-strain behaviour of FRP-confined concrete since the effect of confining stress, concrete strength, hoop and axial strains are inter-related and need to be determined simultaneously. Herein, to better understand and simulate the behaviour of FRP-confined concrete, a stress-strain model has been developed, which consists of the following three main components: (1) A hoop strain equation elaborated from the authors’ previous study on steel-confined concrete columns for application to FRP-confined concrete; (2) A modified confined concrete model considering stress-path of confining stress (or history of hoop strain); (3) Interaction between FRP and concrete. The model was verified based on 321 test results obtained from the literature, the design application of the which to a broad range of FRP-confined concrete structures is thus ensured.
       
  • Ultimate shear resistance of ultra-high performance fiber reinforced
           concrete-normal strength concrete beam
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): He Ji, Chao LiuAbstractThe composite element of ultra-high performance fiber reinforced concrete (UHPFRC) and normal strength concrete (NC) is an effective way to take full advantage of the material properties of UHPFRC and NC. In this paper, the calculation method for UHPFRC-NC composite beams with stirrups based on ultimate equilibrium theory is proposed. The shear resistance of composite beams is divided into three parts: compression zone, stirrups and UHPFRC layer. The shear contribution of stirrups and compression zone is calculated according to the force equilibrium state of the free body of the composite beam. The shear contribution of the UHPFRC layer is calculated based on the fracture pattern of the single hinge in the UHPFRC layer. Then the calculation method is modified considering the size effect. Subsequently, the shear experiment of the UHPFRC-NC composite beams is conducted to test the validity of the calculation method and study the influence of the UHPFRC layer, longitudinal reinforcement and size effect on the composite beams. Meanwhile, the universality of the method is verified based on the cantilever shear experiments of other researchers.
       
  • Finite element model for bolted shear connectors in concrete-filled steel
           tubular columns
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Lucas Ribeiro dos Santos, Hermano de Sousa Cardoso, Rodrigo Barreto Caldas, Lucas Figueiredo GriloAbstractThis research presents a study on the numerical simulation of the structural behavior of bolted shear connectors used as force transfer device in concrete-filled composite columns. The numerical model was developed in ABAQUS software, using the constitutive model named Concrete Damaged Plasticity. In the study, the influence of different concrete stress-strain relationships on tensile and compressive strengths was analyzed, as well as the influence of the use of damage variables. Three different stress-strain relationships on concrete compressive strength were tested, and another three on concrete tensile strength, distinguished by the crack opening displacement. The obtained results were calibrated with the experimental results of four experimental models, and, next, the proposed calibration was compared with twelve other experimental results. Finally, the proposed parameters showed to be suitable to represent the structural behavior of bolted shear connectors applied in force transfer in concrete-filled composite columns.
       
  • Shear resistance of retrofitted castellated link beams: Numerical and
           limit analysis approaches
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Amin Mohebkhah, Mojtaba G. AzandarianiAbstractThis paper deals with the cyclic behavior and shear capacity of non-compact steel castellated link beams (CLBs) using finite element analysis. To enhance the shear resistance and inelastic rotation capacity of such vulnerable link beams, some retrofitting strategies are explored and examined. To this end, a three dimensional finite-element model using ABAQUS is developed for the inelastic nonlinear analysis of the unstiffened and stiffened CLBs. It was found that unstiffened short CLBs cannot reach the required inelastic rotation capacity of 0.08 rad as per the Seismic Provisions for shear links. However, two strengthening strategies were found that can be used to make their cyclic behavior more stable and increase their inelastic rotation capacity to an acceptable value as per the Provisions. Furthermore, in order to determine the ultimate shear resistance of unstiffened and stiffened CLBs, a theoretical formula based on the upper-bound theorem of limit analysis and a refined collapse mechanism was proposed. It was shown that the limit analysis results are in good agreement with the FEA predictions.
       
  • Study on the stiffness degradation and damping of pile foundations under
           dynamic loadings
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Zheng Li, Sandra Escoffier, Panagiotis KotronisAbstractThis paper presents a comprehensive study on the different behaviour of batter and vertical pile foundations in terms of stiffness degradation and damping properties under dynamic loadings. Firstly, dynamic centrifuge tests were carried out and the variations of translational/rotational stiffness and the associated damping properties were identified from a series of hysteretic loops. Results show that for the rocking behaviour, the presence of batter piles causes a small decrease of the rotational stiffness and a great increase of the rotational damping; for the horizontal translation behaviour, batter pile foundation has much higher horizontal stiffness and translational damping compared to the vertical foundation. Then, a set of stiffness degradation and damping curves for the translational and rotational behaviour of batter and vertical pile foundations are proposed. Finally, the proposed stiffness degradation and damping curves were validated numerically by using equivalent linear approach. The numerical validation shows a good agreement with the experimental results.
       
  • Hollow concrete columns: Review of structural behavior and new designs
           using GFRP reinforcement
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): O.S. AlAjarmeh, A.C. Manalo, B. Benmokrane, K. Karunasena, W. Ferdous, P. MendisAbstractHollow concrete columns (HCCs) reinforced with steel bars have been employed extensively for bridge piers, ground piles, and utility poles because they use fewer materials and offer higher structural efficiency compared to solid concrete columns with the same concrete area. Many experimental studies have been conducted to investigate the behavior of HCCs under different loading conditions and found that the structural performance of HCCs is critically affected by many design parameters. If not designed properly, HCCs exhibit brittle failure behavior, due to longitudinal bars buckling or the concrete wall failing in shear. In addition, the corrosion of steel bars has become an issue in reinforced-concrete structures. Therefore, this paper critically reviews the different design parameters that affect the performance of HCCs and identifies new opportunities for the safe design and effective use of this construction system. Moreover, the use of GFRP bars as reinforcement in hollow concrete columns is explored with the aim of developing a non-corroding and structurally reliable construction system.
       
  • Probabilistic analysis of a simple composite blast protection wall system
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Assal Hussein, Hussam Mahmoud, Paul HeyligerAbstractTerrorism has become a major challenge for the world. Terrorist organizations have raised their activities and their attacks in the last years using explosives. These attacks have left numerous numbers of victims, wreaked massive havoc to basic infrastructure, and increased global concern about the nature of these attacks. Blast wall protection systems can provide a required safety level to reduce injuries/casualties in different attack scenarios. Furthermore, installation and procurement costs could be greatly reduced using readily available materials. This paper investigates the performance of a composite wood-sand-wood blast wall by estimating the probability of exceeding a performance limit state for the wall for a suicide vest threat scenario. Fragility curves were devised using direct Monte Carlo simulations to predict the probability of failure of an equivalent simplified single degree-of-freedom system. The simplified model, calibrated to a 3D finite element analysis of the prototype wall, was used to determine the horizontal displacement at the back center of the wall. The analysis framework was developed to probabilistically evaluate the performance of the proposed blast wall in the presence of uncertainties in structural properties and blast load parameters under increasing intensity of the blast. Uncertainties in the random variables were modeled using appropriate statistical distributions. The analyses results show that under certain conditions the wall can provide the required level of protection for the considered threat scenarios.
       
  • New and extended design moment formulations for slender columns in frames
           with sway
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Jostein HelleslandAbstractPresent first-order based design code formulations for slender columns in frames with sway, employ sway magnification factors (for global second-order effects) also as moment magnifiers for the individual columns of the frame (storey). This approach ignores differences in magnification of individual column moments caused by local second-order effects in the columns. This difference can be significant. Better understanding of this aspect will strengthen approximate first-order based elastic methods, for which the important superposition principle is valid. Towards this end, local second-order effects are considered for shears, end moments and maximum moments, applicable over the full range of axial loads. Specifically, end moment and maximum moment expressions of columns with sway are derived. These represent novel contributions that are suitable in typical design code formats, and in practical design work. They will allow more rational column assessments, and will allow more economical designs than present structural code procedures. Proposals are verified by comparison with results from second-order in-plane elastic analyses of single restrained columns and columns in frame panels. Also, extensions to the general case of load combinations that include both gravity and sideways loading are briefly presented.
       
  • Reliability analysis of shear strength of reinforced concrete deep beams
           using NLFEA
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Rafael A. Sanabria Díaz, Silvia J. Sarmiento Nova, Maria C.A. Teixeira da Silva, Leandro Mouta Trautwein, Luiz C. de AlmeidaHighlights•This work investigates the safety level of a deep beam originally designed using the strut-and-tie model.•A methodology is proposed and tested coupling NLFEA and reliability methods for the structural safety assessment.•The probability of failure and the reliability index are obtained using RSM.•A sensitivity analysis is carry out to identify the key parameters for a deep beam reliability assessment.AbstractNonlinear finite element analysis (NLFEA) is an important tool for solving deterministic structural problems and predicting the behavior of concrete structures. Nevertheless, inherent uncertainties in structural engineering cannot be considered using deterministic approaches. For that reason, the inclusion of reliability concepts in NLFEA has been a frequent subject in recent investigations. This work aims to study the safety of the design of reinforced concrete deep beams. This is done by coupling the finite element analysis and reliability theory approaches. The assessment of the shear capacity of deep beams involves different phenomenons such as discontinuity regions and size effect. Therefore, this cannot be designed or analyzed by simple calculations. In this study, a simply supported deep beam designed with the strut-and-tie method (STM) is used as an example of structural reliability assessment. The nonlinear analyses were performed in the software ATENA, based on concrete fracture and plasticity theory. For reducing computational effort, the reliability analysis was performed using two different Response Surface Method (RSM) strategies. Uncertainties from concrete properties and geometrical dimensions were considered using probability density functions. As a result, the safety of the deep beam design was expressed in terms of the reliability index β and the probability of failure Pf. According to the results obtained, the conclusion was that NLFEA combined with the reliability theory concept can allow an advanced safety assessment of deep beam design.
       
  • Out-of-plane closed-form solution for the seismic assessment of
           unreinforced masonry schools in Nepal
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Nicola Giordano, Flavia De Luca, Anastasios SextosAbstractTraditional unreinforced masonry (URM) constructions still represent an important part of the school building stock in several low-income countries including Nepal. Unfortunately, their intrinsic vulnerability impacts negatively on the resilience of cities and local communities. Observations after major seismic events have shown that the predominant mode of failure is the out-of-plane (OOP) of the weak and loosely connected perimeter masonry walls which typically leads to partial or global collapse. Starting from this evidence, a closed-form analytical approach is presented aimed at deriving the OOP force-displacement response of URM walls for different boundary conditions and vertical loads. The novel analytical solution is successfully validated with the results of seventeen OOP experimental tests on URM walls available in the literature. Then, referring to a case-study Nepalese school building, capacity curves of the constituting walls are derived and adopted for the vulnerability assessment of the structure through the Capacity Spectrum Method (CSM) where equivalent hysteretic damping is calibrated with available OOP shaking table test results. Lastly, PGA capacities for different damage states are successfully compared with median values from observational fragility curves.
       
  • Measuring bridge frequencies by a test vehicle in non-moving and moving
           states
    • Abstract: Publication date: 15 January 2020Source: Engineering Structures, Volume 203Author(s): Y.B. Yang, Hao Xu, Bin Zhang, Feng Xiong, Z.L. WangAbstractThis paper presents the measurement results of bridge frequencies by a test vehicle in non-moving and moving states. The self-made test vehicle fitted with vibration sensors is a two-wheel trailer, intentionally used to simulate the theoretical single degree-of-freedom system. The two-span bridge selected is located in the Chongqing University campus. For the purpose of comparison, the bridge frequencies were firstly measured by direct deployment of vibration sensors on the bridge. The dynamic properties of the test vehicle in the non-moving state, including the transmissibility, are examined in detail. Based on the measured car-body response, the contact-point response of the vehicle with the bridge was calculated by a backward procedure that allows the vehicle frequency to be eliminated. It was found that the vehicle in the non-moving state can catch more bridge frequencies than in the moving state. Both the car-body and contact-point responses agree well the results by direct measurement. But the contact-point response performs better than the car-body response, which can be used to detect the first few frequencies of the bridge, including the torsional frequency.
       
  • Study on failure mechanism of prestressed concrete containments following
           a loss of coolant accident
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): Zefang Wang, Jiachuan Yan, Youzhu Lin, Tao Fang, Jialu MaAbstractA loss of coolant accident (LOCA) is considered as a severe accident in the safety of nuclear power plant. LOCA has significant negative influences on the containment structures. Because the characteristics of temperature variation are instantaneous, the thermal field in the inner wall of the containment has a remarkably non-uniform distribution, which leads to complex mechanical behavior. In this study, the distribution of the thermal field of a prestressed concrete containment vessel (PCCV) at different times under a LOCA is analyzed. On this basis, the mechanical behavior of the PCCV under the coupling effect of thermal load and internal pressure are systematically investigated, and the failure mechanism and failure mode of the structure are revealed. The results show that the structure fails with a large deformation near the largest hole and evident expansion at the dome considering the thermal load. However, the deformation develops deficiently under the high temperature of the LOCA. Finally, design suggestions are proposed for a containment under thermal–pressure coupling action.
       
  • Experimental investigation of glued-laminated timber beams with
           Vectran-FRP reinforcement
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): Bruno F. Donadon, Nilson T. Mascia, Ramon Vilela, Leandro M. TrautweinAbstractThe growing interest in sustainable buildings has inspired the improvement of timber structures in the construction market. As a raw material, wood may present natural defects that can cause changes in its mechanical properties, such as strength reduction, as well as brittle failure under tension, which limit the application of this material in construction. In recent decades, synthetic fibers with high tensile strength are available as construction material, and research to evaluate the efficiency of synthetic fibers and adhesive composites as a reinforcement for glued-laminated timber beams has been carried out. This paper deals with an experimental study applying bending tests to glue-laminated timber beams made of Pinus Elliottii, a low-strength wood class originated from reforestation, and strengthened with fiber reinforced polymers of Vectran fibers and epoxy adhesive. A numerical procedure based on the finite element method is also developed to compare with experimental results. Vectran is a synthetic thermoplastic fiber with high mechanical properties, however, its potential application as reinforcement material in structural pieces is still poorly explored. The results obtained in this work demonstrated that the application of Vectran-FRP reinforcement to glued-laminated timber beams provided both an increase of 19.48 to 34.95% in elastic regime stiffness and of 7 to 40% in ultimate load, when compared with unreinforced similar beams. Numerical analysis adequately confirmed the experimental results on elastic behavior, while in the non-elastic phase it revealed a considerable difference. A reduction in the rupture coefficient of variation regarding the reinforced beams was also verified. In addition, the application of fibers as structural reinforcement changed the timbeŕs failure mode from brittle in tension to ductile in compression. The results show that Vectran fibers are mechanically efficient as reinforcement, with perspectives of application in construction.
       
  • Probabilistic estimation of floor response spectra in masonry infilled
           reinforced concrete building portfolio
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): Daniele Perrone, Emanuele Brunesi, Andre Filiatrault, Roberto NascimbeneAbstractThe seismic performance of non-structural elements is now recognized to be a key issue in the seismic assessment and earthquake related loss estimation of buildings, both at the individual and regional scale. The evaluation of the seismic demand on non-structural elements in many modern building codes is often based on inaccurate distributions of floor accelerations. For this reason, some design oriented simplified methodologies have been developed recently to predict floor response spectra in reinforced concrete buildings. Although the influence of masonry infills on the seismic performance of reinforced concrete buildings has been widely demonstrated, infills are generally neglected both in the design and in the evaluation of floor response spectra, which could lead to un-conservative design of non-structural elements. In this paper, the effect of masonry infills on absolute acceleration and relative displacement floor response spectra for reinforced concrete buildings subjected to frequent (serviceability level) earthquakes is investigated through a probabilistic framework. A database of one hundred masonry infilled reinforced concrete frames, representative of the European context, was generated and each building analyzed through nonlinear time history analyses. From the results of these analyses, the acceleration and displacement response spectra at different floor levels of both bare and infilled frame archetypes were then computed. The effectiveness of the most common assumptions made in regional risk models to estimate the non-structural losses is investigated and a first attempt at a more refined approach taking into account the effect of masonry infills is proposed.
       
  • Optimum performance-based design of eccentrically braced frames
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): Mohammad Ali Fathali, Seyed Rohollah Hoseini VaezAbstractOne new design method that is currently under consideration by researchers is performance-based design (PBD). This method has been evaluated using different criteria and definitions. In the current study, the weight optimization problem is defined using PBD to consider more constraints than have been considered in other studies in this field. The problem has been formulated for eccentrically braced frame (EBF) structures. Thus far, weight optimization of EBFs using PBD has not been attempted. For this reason, the main objective has been to examine the possibility of optimizing the EBF weight based on PBD. A new method for modeling of the link beam has been used to evaluate its behavior. Structural analysis has been done using nonlinear static analysis (pushover). The performance of the proposed optimization process is demonstrated for the optimal design of two 2D EBF structures using four different metaheuristic algorithms.
       
  • Predicting residual deformations in a reinforced concrete building
           structure after a fire event
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): Shuna Ni, Thomas GernayAbstractReinforced concrete (RC) structures often remain stable under fire, but exhibit damage and residual deformations which require repairs. While repair operations and building downtime are expensive, current fire design approaches do not consider post-event resilience. The first step to enable predicting the resilience of RC structures under fire is to develop capabilities to model the damage of these structures after various fire exposures. This paper focuses on the prediction of the residual (post-fire) deformations of RC columns within a code-designed five-story RC frame building. Computational modeling approaches to capture the fire behavior of the columns are investigated. The models range from isolated columns with linear springs at the boundaries to full building model coupling beam and shell elements, with intermediate approaches. The analyses highlight the critical nonlinear role of the thermal expansion-contraction of the surrounding beams and slabs on the column deformations. Large transversal residual deformations develop particularly in perimeter columns, combined with residual shortening. This invalidates models based on isolated column or 2D frame. A parametric study of the residual deformations of RC columns is then conducted, with due consideration of the 3D restraints and interactions, to investigate the effects of different design parameters and fire scenarios on the residual deformations after a fire event. The results of the parametric study indicate that fire load density and opening factor significantly influence the residual deformations of RC columns, compared to the thermal conductivity of concrete and live loads. This research improves the understanding and provides recommendations for numerical modeling of the effect of fire on the residual capacity and deformations in RC structures.
       
  • Slow dynamics process observed in civil engineering structures to detect
           structural heterogeneities
    • Abstract: Publication date: 1 January 2020Source: Engineering Structures, Volume 202Author(s): Philippe Guéguen, Marc-Antoine Brossault, Philippe Roux, Juan Carlos SingauchoAbstractUnder strong seismic excitation, the resonance frequencies of civil engineering structures rapidly decrease, followed by slow recovery back to their initial values if there is no damage. In this study, we show that as for laboratory trials with rock samples, the properties of the slow recovery characterise the level of heterogeneities, and in this case, the damage rate. First, we validate this concept with laboratory tests applied to continuous beam-like structures in damaged and undamaged states. One recent model is used to fit the observed recoveries, and we show that its parameters (i.e., frequency variation, recovery slope, characteristic times) change with the health of the equivalent structure. In a second step, this concept is applied to two civil engineering structures that experience earthquakes: the first (Factor Building, USA) without observed damage; and the second (Geophysics Institute building, Ecuador) that experienced a fore/ main/ after-shock sequence with apparent damage that was characterised by a permanent drop in resonance frequency. The efficiency of the proposed model is confirmed for monitoring and for the fit of the frequency recovery. We conclude that the recovery process is a clear proxy of the structural state, and that this could be helpful for seismic monitoring of structural health during earthquake sequences.
       
 
 
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