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  First | 1 2 3 4 5     

Journal Cover   Soil Dynamics and Earthquake Engineering
  [SJR: 1.482]   [H-I: 45]   [8 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0267-7261
   Published by Elsevier Homepage  [2812 journals]
  • A synthetic formulation for the Italian seismic hazard and code
           implications for the seismic risk
    • Abstract: Publication date: October 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 77
      Author(s): I. Vanzi , G.C. Marano , G. Monti , C. Nuti
      The paper contains two parts. In the first one, the seismic hazard on the Italian territory, as given by the current Italian structural design code, published in 2008, is discussed. Hazard curves, given by the Italian code in a tabular form, are fitted with a single non-linear model and it is shown that a more compact, simple and user-ready territorial hazard description can be applied. The model is valid for both the bedrock and the surface seismic hazards, and is accurate. The surface seismic hazard is computed with a local amplification mapping, which is now well detailed over the entire territory. Departing from these results, in the second part the territorial seismic risk for the ultimate limit state is computed via a parametric fragility curve. From the results, it can be inferred that the codes need further factors calibration, with the aims of guaranteeing both territorially uniform reliability levels, and the traditionally assumed target reliability levels, e.g. those stated in the Eurocodes.


      PubDate: 2015-05-25T08:01:19Z
       
  • Real-valued modal response history analysis for asymmetric-plan buildings
           with nonlinear viscous dampers
    • Abstract: Publication date: October 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 77
      Author(s): Jui-Liang Lin , Tze-How Liu , Keh-Chyuan Tsai
      Modal analysis, which is clear in concept and simple in computation, is widely applied to evaluate the seismic responses of elastic structures with proportional damping. Nevertheless, nonlinear viscous dampers commonly installed in real buildings result in non-proportionally damped structures, which impede the modal analysis in real number field for such structures. This study develops the approach of performing real-valued modal response history analysis for elastic two-way asymmetric-plan buildings with nonlinear viscous dampers. To this end, this study first constructs the nonlinear three-degree-of-freedom (3DOF) modal equations of motion for such structures. The nonlinear 3DOF modal equations of motion retain the non-proportional damping characteristics in the modal space. Hence, by solving the nonlinear 3DOF modal equations of motion, the total response history is effectively attained by arithmetically summing up the modal response histories. This study uses nine two-way asymmetric-plan buildings, each equipped with nonlinear viscous dampers subjected to three bi-directional ground motions to verify the proposed approach. The investigation results show that the proposed simplified analysis approach provides satisfactory estimation of the seismic responses of common asymmetric-plan buildings with nonlinear viscous dampers.


      PubDate: 2015-05-25T08:01:19Z
       
  • Effects of site stiffness and source to receiver distance on surface wave
           tests׳ results
    • Abstract: Publication date: October 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 77
      Author(s): Jyant Kumar , Tarun Naskar
      By using six 4.5Hz geophones, surface wave tests were performed on four different sites by dropping freely a 65kg mass from a height of 5m. The receivers were kept far away from the source to eliminate the arrival of body waves. Three different sources to nearest receiver distances (S), namely, 46m, 56m and 66m, were chosen. Dispersion curves were drawn for all the sites. The maximum wavelength (λ max ), the maximum depth (d max ) up to which exploration can be made and the frequency content of the signals depends on the site stiffness and the value of S. A stiffer site yields greater values of λ max and d max . For stiffer sites, an increase in S leads to an increase in λ max . The predominant time durations of the signals increase from stiffer to softer sites. An inverse analysis was also performed based on the stiffness matrix approach in conjunction with the maximum vertical flexibility coefficient of ground surface to establish the governing mode of excitation. For the Site 2, the results from the surface wave tests were found to compare reasonably well with that determined on the basis of cross boreholes seismic tests.


      PubDate: 2015-05-25T08:01:19Z
       
  • Cyclic and post-cyclic monotonic behavior of Adapazari soils
    • Abstract: Publication date: October 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 77
      Author(s): Zulkuf Kaya , Ayfer Erken
      The August 17, 1999 Kocaeli earthquake affected the city of Adapazari, which is located in the northwest of Turkey, with severe liquefaction and bearing capacity failures causing tilting of buildings, excessive settlements and lateral displacements. To understand the stress–strain behavior and pore pressure behavior of undisturbed soils during the earthquake, the cyclic and post-cyclic shear strength tests have been conducted on soil samples obtained from Adapazari in a cyclic triaxial test system within the scope of this research. Cyclic tests have been conducted under stress controlled and undrained conditions. Post-cyclic monotonic tests have been conducted following cyclic tests. The strength curves obtained in the experiments showed that the dynamic resistance of silty sand was found to be 45% lower than those of high plasticity soils (MH). The strength of clayey soils with the plasticity index of PI=15–16% was lower compared to the strength of high plasticity soils. Also, it was observed that silty sand soils had the lowest strength. The dynamic strength of the soils increased with the increase in plasticity.


      PubDate: 2015-05-25T08:01:19Z
       
  • Pre-shear effect on liquefaction resistance of a Fujian sand
    • Abstract: Publication date: October 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 77
      Author(s): Bin Ye , Jiafeng Lu , Guanlin Ye
      Pre-shear history has been shown to be a critical factor in the liquefaction resistance of sand. By contrast to prior experimental studies in which triaxial shear tests were used to examine the effects of pre-shear on the liquefaction resistance of sand, hollow cylinder torsional shear tests were used in this study to avoid the influence of the inherent anisotropy that is inevitably produced during the sample preparation process because of gravitational deposition. A series of cyclic undrained shear tests were performed on sand samples that had experienced medium to large pre-shear loading. The test results showed that the liquefaction resistance of sand can be greatly reduced by its pre-shear history, and a pre-shear strain within the range from 0.1% to 5% can cause sand to be more prone to liquefaction. During the cyclic shear tests, the samples that had experienced pre-shear loading exhibited different behaviors when cyclic shear loading started in different directions, i.e., the clockwise direction and the counterclockwise direction. If the cyclic loading started in the identical direction as the pre-shear loading, then the mean effective stress of the sand was almost unchanged during the first half of the loading cycle; if the cyclic loading started in the direction opposite to that of the pre-shear loading, then the mean effective stress decreased significantly during the first half of the loading cycle. However, this anisotropic behavior was only remarkable during the first loading cycle. From the second cycle onward, the speeds of the decrease in the mean effective stresses in the two types of shear tests became similar.


      PubDate: 2015-05-20T07:46:33Z
       
  • A new expression for determining the bending stiffness of circular
           micropile groups
    • Abstract: Publication date: October 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 77
      Author(s): Keyvan Abdollahi , Alireza Mortezaei
      Increased bending stiffness and decreased foundation rotation are two main factors which reduce the rocking motion of foundation. A micropile group in circular arrangement is an innovative technique for reducing the rocking motion of the foundation. In this paper, the effects of several parameters were numerically investigated on the rocking stiffness of circular micropile group foundations. The finite difference software FLAC3D was used to model the foundation, soil, and the structure. The micropiles used in this study varied in the diameter, but had similar length. A total of seven records were selected to cover a wide range of frequency content, duration and amplitude. The results from the numerical simulation were compared and verified against those obtained from an alternative numerical method as well as a set of experimental test results. The model was then used for parametric studies and the effects of relevant parameters were investigated. The results showed that slenderness, inclination angle and distance ratio of a micropile group are main factors which increase the soil stiffness and control the seismic motion of high-rise buildings. Based on the results, a new expression was proposed that can be used to determine the optimal moment of inertia of circular micropile groups. The proposed expression revealed that the primary factors which reduce the effective period of the buildings are the number, diameter, and injection pressure of micropiles in a circular micropile group. Using the proposed relationship, it was found that using circular micropile groups can reduce the destructive seismic effects (i.e. drift demand) in high-rise buildings by up to 60%.


      PubDate: 2015-05-20T07:46:33Z
       
  • Vibration control of piled-structures through
           structure-soil-structure-interaction
    • Abstract: Publication date: October 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 77
      Author(s): Pierfrancesco Cacciola , Maria Garcia Espinosa , Alessandro Tombari
      This paper deals with the vibration control of existing structures forced by earthquake induced ground motion. To this aim it is proposed for the first time to exploit the structure–soil–structure mechanism to develop a device, hosted in the soil but detached from the structure, able to absorb part of the seismic energy so to reduce the vibration of neighbourhood structures. The design of the device is herein addressed to protect monopile structures from earthquake induced ground motion. By modelling the ground motion as zero-mean quasi-stationary response-spectrum-compatible Gaussian stochastic process, the soil as visco-elastic medium and the target monopiled-structure as a linear behaving structure the device, herein called Vibrating Barrier (ViBa), has been designed through an optimization procedure. Various numerical and experimental results are produced to show the effectiveness of the ViBa. Remarkably, a significant reduction of the structural response up to 44% has been achieved.


      PubDate: 2015-05-20T07:46:33Z
       
  • A surface seismic approach to liquefaction
    • Abstract: Publication date: October 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 77
      Author(s): Silvia Castellaro , Riccardo Panzeri , Flaminia Mesiti , Lara Bertello
      The liquefaction potential of soils is traditionally assessed through geotechnical approaches based on the calculation of the cyclical stress ratio (CSR) induced by the expected earthquake and the ‘resistance’ provided by the soil, which is quantified through standard penetration (SPT), cone penetration (CPT), or similar tests. In more recent years, attempts to assess the liquefaction potential have also been made through measurement of shear wave velocity (V S) in boreholes or from the surface. The latter approach has the advantage of being non-invasive and low cost and of surveying lines rather than single points. However, the resolution of seismic surface techniques is lower than that of borehole techniques and it is still debated whether it is sufficient to assess the liquefaction potential. In this paper we focus our attention on surface seismic techniques (specifically the popular passive and active seismic techniques based on the correlation of surface waves such as ReMiTM, MASW, ESAC, SSAP, etc.) and explore their performance in assessing the liquefaction susceptibility of soils. The experimental dataset is provided by the two main seismic events of M L=5.9 and 5.8 (M W=6.1, M W=6.0) that struck the Emilia-Romagna region (Northern Italy) on May 20 and 29, 2012, after which extensive liquefaction phenomena were documented in an area of 1200km2. The CPT and drillings available in the area allow us to classify the soils into four classes: A) shallow liquefied sandy soils, B) shallow non-liquefied sandy soils, C) deep non-liquefied sandy soils, and D) clayey–silty soils, and to determine that on average class A soils presented a higher sand content at the depth of 5–8m compared to class B soils, where sand was dominant in the upper 5m. Surface wave active–passive surveys were performed at 84 sites, and it was found that they were capable of discriminating among only three soil classes, since class A and B soils showed exactly the same V S distribution, and it is possible to show both experimentally and theoretically that they appear not to have sufficient resolution to address the seismic liquefaction issue. As a last step, we applied the state-of-the art CSR–V S method to assess the liquefaction potential of sandy deposits and we found that it failed in the studied area. This might be due to the insufficient resolution of the surface wave methods in assessing the Vs of thin layers and to the fact that Vs scales with the square root of the shear modulus, which implies an intrinsic lower sensitivity of Vs to the shear resistance of the soil compared to parameters traditionally measured with the penetration tests. However, it also emerged that the pure observation of the surface wave dispersion curves at their simplest level (i.e. in the frequency domain, with no inversion) is still potentially informative and can be used to identify the sites where more detailed surveys to assess the liquefaction potential are recommended.


      PubDate: 2015-05-20T07:46:33Z
       
  • Determining anti-plane responses induced by oblique-truncated semicircular
           canyon using systematic hybrid method with mapping function
    • Abstract: Publication date: October 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 77
      Author(s): Wen-Shinn Shyu , Tsung-Jen Teng , Chuen-Shii Chou
      This paper proposes a novel strategy for the investigation of displacement amplitude ( u y ) near and along an oblique-truncated semicircular canyon subjected to shear horizontal (SH) waves. Transfinite interpolation (TFI) was used to obtain the coordinates of nodes and determine the sequence of node numbering in the inner finite region including the canyon. The hybrid method, comprising finite element method and a Lamb series, was applied in conjunction with TFI to study the effects of canyon geometry, incident angle of SH waves ( θ ), and dimensionless frequency ( η ) on u y . We detailed the amplification of u y in the illuminated zone and variations in u y due to canyon-decay-effect along the canyon surface as well as the decay of u y resulting from the shield effect in the shadow zone. Interestingly, oblique-effects play an important role in the magnification of u y along the inclined bottom of canyons, and variations in θ and η dominate the patterns of u y .
      Graphical abstract image

      PubDate: 2015-05-20T07:46:33Z
       
  • Rotational components in structural loading
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): M.R. Falamarz-Sheikhabadi , M. Ghafory-Ashtiany
      In this paper, the rotational loading pattern of multi-storey buildings supported on the spread and continuous interconnected single foundations is discussed. To achieve this, simplified relations for the estimation of (1) point rotations; (2) spatial variation of strong ground motions, and (3) foundation input motions are derived. The height-wise variation of the earthquake rotational loading of multi-storey buildings is parametrically evaluated by considering the location of the first rigid floor diaphragm and foundation type. In addition, the effect of the kinematic soil–structure interaction on the response spectrum of the rotational and translational components is studied. The numerical results provide a deeper insight into the rotational loading of structures in the middle-field zone, and show how the rotational components may detrimentally affect the structural response of multi-storey buildings depending on their kinematic characteristics.


      PubDate: 2015-05-16T10:59:38Z
       
  • Plane strain dynamic response of a transversely isotropic multilayered
           half-plane
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): Zhi Yong Ai , Yi Fan Zhang
      A semi-analytical method is developed to analyze the plane strain dynamic response of a transversely isotropic multilayered half-plane subjected to a time-harmonic surface or buried load. On the basis of the governing equations of motion in Cartesian coordinates, the analytical layer-elements of a single layer with a finite thickness and a half-plane are obtained through the Fourier transform and the corresponding algebraic operations. The analytical layer-element solution for the multilayered half-plane in the transformed domain can be derived in combination with the continuity conditions between two adjacent layers. After the boundary conditions are introduced, the corresponding solution in the frequency domain is recovered by the inverse Fourier transform. The comparison with an existing solution for an isotropic half-plane confirms the accuracy of the proposed method. Several examples are given to portray the influence of material anisotropy, the depth of external load, material stratification and the frequency of excitation on the vertical displacement and vertical normal stress.


      PubDate: 2015-05-16T10:59:38Z
       
  • On the rocking–sliding instability of rigid blocks under ground
           excitation: Some new findings
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): Anthony N. Kounadis
      Rocking (overturning) instability analyses of rigid blocks based on the assumption that the friction between the block and the ground is sufficiently large to exclude the effect of sliding, are reconsidered by including the effect in question. Both modes of overturning instability – without impact and after one impact – are thoroughly discussed in connection with small sliding, whose value depends on the values of kinetic (dry) friction coefficient and the external frequency excitation. Using an energy approach the analytical derivation of the nonlinear differential equations of motion of free-standing rigid blocks under one-sine ground pulse including the effect of sliding, are comprehensively established. The serious difficulties in solving this problem on one hand the change of the kinetic friction coefficient during the motion and on the other hand the reliable evaluation of the actual friction effect when rocking is included, are effectively confronted. This is achieved through a reliable approximation of an equivalent (reduced) coefficient assuming that the major part of friction takes place from the initiation of motion and terminates shortly after the onset of rocking. In cases of slender blocks closed form solutions for overturning due to simultaneous rocking–sliding without or after one impact, are conveniently derived. Among other findings, it was explored that the single block in question for small values of the external frequency (long periods of excitation) the sliding effect is beneficial (stabilizing the block), while for large values of external frequency this effect is detrimental (destabilizing the block).


      PubDate: 2015-05-16T10:59:38Z
       
  • Newmark sliding block model for pile-reinforced slopes under earthquake
           loading
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): A.H. Al-Defae , J.A. Knappett
      Recent studies have demonstrated that the use of a discretely-spaced row of piles can be effective in reducing the deformations of slopes in earthquakes. In this paper, an approximate strain-dependant Newmark sliding-block procedure for pile-reinforced slopes has been developed, for use in analysis and design of the piling scheme, and the model is validated against centrifuge test data. The interaction of the pile within the slipping soil was idealised using a non-linear elasto-plastic (P–y) model, while the interaction within the underlying stable soil was modelled using an elastic response model in which (degraded) soil stiffness is selected for an appropriate amount of shear strain. This combined soil–pile interaction model was incorporated into the improved Newmark methodology for unreinforced slopes presented by Al-defae et al. [1], so that the final method additionally incorporates strain-dependent geometric hardening (slope re-grading). When combined with the strain-dependent pile resistance, the method is therefore applicable to analysis of both the mainshock and subsequent aftershocks acting on the deformed slope. It was observed that the single pile resistance is mobilised rapidly at the start of a strong earthquake and that this and the permanent slope deformation are therefore strongly influenced by pile stiffness properties, pile spacing and the depth of the slip surface. The model shows good agreement with the centrifuge test data in terms of the prediction of permanent deformation at the crest of the slope (important in design for selecting an appropriate pile layout/spacing i.e. S/B) and in terms of the maximum permanent bending moments induced in the piles (important for appropriate structural detailing of the piles), so long as the slip surface depth can be accurately predicted. A method for doing this, based on limit analysis, is also presented and validated.


      PubDate: 2015-05-16T10:59:38Z
       
  • The role of aftershocks in the liquefaction phenomena caused by the Emilia
           2012 seismic sequence
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): Lorenzo Sinatra , Sebastiano Foti
      Extensive and spectacular phenomena of soil liquefaction were observed during the Emilia seismic sequence that struck northern Italy on May–June 2012. A back-analysis with simplified procedures based on empirical correlations reveals a small liquefaction potential, which apparently underestimates the observed surface effects. Multiple and close-in-time events were a peculiar aspect of the sequence but cannot be accounted for within the simplified procedure. This study investigates their possible role in excess pore pressure build-up and hence liquefaction triggering. Results of a numerical analysis suggest that aftershocks played a determinant role, leading liquefaction phenomena to such a great extent as observed in the field. This evidence is to be considered when assessing the results obtained with empirical correlations.


      PubDate: 2015-05-16T10:59:38Z
       
  • Inspection of a high-cycle accumulation model for large numbers of cycles
           (N=2 million)
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): T. Wichtmann , T. Triantafyllidis
      The high-cycle accumulation (HCA) model for sand proposed by Niemunis et al. (2005) [16] has been developed based on numerous drained cyclic triaxial tests with 100,000 cycles. In the present paper the validity of the HCA model, in particular its function f N and flow rule m, for larger numbers of cycles is inspected. For that purpose, drained long-term cyclic triaxial tests with 2 million cycles have been performed on 13 clean quartz sands with different grain size distribution curves. For all tested sands, the function f N , describing the shape of the strain accumulation curves ε acc ( N ) , has been found suitable up to 2 million cycles. The same applies to the cyclic flow rule m, determining the ratio of the volumetric and deviatoric strain accumulation rates. Based on the data from the long-term tests, correlations between the HCA material parameters entering f N and characteristics of the grain size distribution curve (d 50 and C u ) have been improved for the application to 2 million cycles. These correlations are suitable for a simplified calibration of the HCA model and were validated up to 100,000 cycles only so far.


      PubDate: 2015-05-16T10:59:38Z
       
  • A simplified 3 D.O.F. model of A FEM model for seismic analysis of a silo
           containing elastic material accounting for soil–structure
           interaction
    • Abstract: Publication date: October 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 77
      Author(s): Ayşegül Durmuş , Ramazan Livaoglu
      The purpose of this study is the evaluation of dynamic behavior induced by seismic activity on a silo system, containing bulk material, with a soil foundation. The interaction effects between the silo and bulk material, as well as the effects produced between the foundation of the silo and the soil, were taken into account. Proposed simplified approximation, as well as the finite model, were used for analysis. The results, from the presented approximation, were compared with a more rigorous obtainment method. Initially, the produced simplified approximation, with elastic material assumption for the grain, could determine the pressures on the dynamic material along with displacements along the height of the silo wall and base shear force, etc., with remarkable precision. Some comparisons, via a change of soil and/or foundation conditions, were also made regarding the seismic pressure of the dynamic material pressure, displacement and base shear forces for both squat and slender silos. Comparing the analytical predictions to results from the numerical simulations produced good results. It can be concluded that the model can be used effectively to perform a broad suite of parametric studies, not only at the design stage but also as a reliable tool for predicting system behavior under the limit state of the system. The results and comprehensive analysis show that displacement effects and base shear forces generally decreased when soil was softer; however, soil structure interaction (SSI) did not have any considerable effects on squat silos and therefore need not be taken into practice.


      PubDate: 2015-05-16T10:59:38Z
       
  • Postliquefaction behavior of low-plasticity silt at various degrees of
           reconsolidation
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): Shuying Wang , Ronaldo Luna , Site Onyejekwe
      During earthquake events, low-plasticity silt undergoes a reduction in shear strength and stiffness due to development of excess pore pressure induced by cyclic loading. With reconsolidation, during which process excess pore pressure is dissipated, the shear strength and stiffness can be regained. However, due to the low permeability of silts (compared to sands), the dissipation of excess pore pressure and the reconsolidation of low-plasticity silt takes much more time. This paper investigates the postliquefaction shear behavior of Mississippi River Valley (MRV) silt at various degrees of reconsolidation using triaxial tests. Test results indicate that there was a steady increase, in shear strength and stiffness, at both large and small deformations, with increase in the degree of reconsolidation. The postliquefaction silt showed the effect of the apparent OCR, which had a close effect on postcyclic shear behavior as did the OCR on the static behavior. The critical state lines of MRV silt were different for pre- and post-liquefaction conditions.


      PubDate: 2015-05-16T10:59:38Z
       
  • Assessment of the seismic performance of a bituminous faced rockfill dam
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): Matteo Albano , Giuseppe Modoni , Paolo Croce , Giacomo Russo
      In the attempt to codify a procedure exportable to other similar cases, a thorough investigation of the seismic performance of a bituminous concrete faced rockfill dam built in Italy in the early eighties is herein presented. The dam presents a 90m tall embankment built in a narrow canyon and is situated in a highly seismic region. The implemented methodology encompasses the indications provided by the most recent literature to point out the problems potentially caused by earthquakes and to account for the paramount factors affecting the response of the dam. Particular attention has been paid to the concept of performance, defining its goals in accordance with the most recent standards and deriving the correspondent limit conditions from observations reported in the literature. In order to optimize the computational effort, dynamic analyses with two and three dimensional finite difference codes have been combined to study the coupled response of the embankment, rocky foundation and bituminous facing. After validating the numerical models with centrifuge tests performed on small scale models of the embankment, the performance of the dam has been investigated with reference to a number of possible scenarios focusing on the amplification spectra, the deformation of the embankment and the integrity of the bituminous lining.


      PubDate: 2015-05-07T06:23:43Z
       
  • Grey Wolf Optimizer for parameter estimation in surface waves
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): Xianhai Song , Li Tang , Sutao Zhao , Xueqiang Zhang , Lei Li , Jianquan Huang , Wei Cai
      This research proposed a novel and powerful surface wave dispersion curve inversion scheme called Grey Wolf Optimizer (GWO) inspired by the particular leadership hierarchy and hunting behavior of grey wolves in nature. The proposed strategy is benchmarked on noise-free, noisy, and field data. For verification, the results of the GWO algorithm are compared to genetic algorithm (GA), the hybrid algorithm (PSOGSA)-the combination of Particle Swarm Optimization (PSO) and Gravitational Search Algorithm (GSA), and gradient-based algorithm. Results from both synthetic and real data demonstrate that GWO applied to surface wave analysis can show a good balance between exploration and exploitation that results in high local optima avoidance and a very fast convergence simultaneously. The great advantages of GWO are that the algorithm is simple, flexible, robust and easy to implement. Also there are fewer control parameters to tune.


      PubDate: 2015-05-03T06:08:40Z
       
  • Reply on “Implications of surface wave data measurement uncertainty
           on seismic ground response analysis”
    • Abstract: Publication date: July 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 74
      Author(s): Ravi Sankar Jakka , Narayan Roy , H.R. Wason
      We are thankful to Comina and Foti [1] (‘The Discussers’), who showed their interest in our research and raised some issues on our paper on the “Implications of surface wave data measurement uncertainty on seismic ground response analysis”. Their main concerns [1] are on the selection criteria that we adopted to select the equivalent profiles, requirement of multimodal inversion and the seismic response of those equivalent profiles. We have prepared here a detailed explanation on all the raised issues and it is shown that the variations in spectral parameters are not merely due to the so-called discrepancies raised by ‘The Discussers’.


      PubDate: 2015-05-03T06:08:40Z
       
  • Discussion on “Implications of surface wave data measurement
           uncertainty on seismic ground response analysis” by Jakka et al.
    • Abstract: Publication date: July 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 74
      Author(s): Cesare Comina , Sebastiano Foti
      The discussion deals with the effect of shear wave velocity uncertainties on 1D seismic ground response analysis. In particular, the paper refers to uncertainties deriving from the solution of the inverse problem in surface wave methods. We address some issues related to the evaluation of “equivalent” profiles from surface wave data, the inversion strategy and the numerical simulation of seismic site response. The pitfalls in the analyses point out the need for more refined studies to draw general conclusions on the subject.


      PubDate: 2015-05-03T06:08:40Z
       
  • Editorial Board / Aims and Scope
    • Abstract: Publication date: July 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 74




      PubDate: 2015-05-03T06:08:40Z
       
  • 2011 Sikkim Earthquake at Eastern Himalayas: Lessons learnt from
           performance of structures
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): Sekhar Chandra Dutta , Partha Sarathi Mukhopadhyay , Rajib Saha , Sanket Nayak
      On 18 September 2011, all the Indian states and countries surrounding Sikkim witnessed a devastating moderate earthquake of magnitude 6.9 (Mw). Originating in Sikkim–Nepal border with an intensity of VI+ in MSK scale, this earthquake caused collapse of both unreinforced masonry buildings, heritage structures and framed structures followed by landslides and mud slides at various places of Sikkim. Significant damages have been observed in relatively new framed structures mainly in Government buildings, thick masonry structures, while, the older wooden frame (ekra) non-engineered structures performed well during the earthquake. Further, it is noteworthy that government buildings suffered more than private ones and damages were observed more in newer framed structures than older ones. Analysis of the damages identify lateral spreading of slope, pounding of buildings, out-of-plane rotation, generation of structural cracks, plastic hinge formation at column capitals and damage of infill wall material as predominant damage features. A few remedial measures are also attempted to be mentioned with future need of research and application. It has been felt to create awareness regarding these issues and is the need of the hour.


      PubDate: 2015-05-03T06:08:40Z
       
  • Time-domain analysis of wave propagation in 3-D unbounded domains by the
           scaled boundary finite element method
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): Xiaojun Chen , Carolin Birk , Chongmin Song
      Transient wave propagation in three-dimensional unbounded domains is studied. An efficient numerical approach is proposed, which is based on using the displacement unit-impulse response matrix representing the interaction force–displacement relationship on the near field/far field interface. Spatially, an approximation is used to reduce the computational effort associated with the large size of three-dimensional problems. It is based on subdividing the fully coupled unbounded domain into multiple subdomains. The displacement unit-impulse response matrices of all subdomains are calculated separately. The error associated with this spatial decoupling can be reduced by placing the near field/far field interface further away from the domain of interest. Detailed parameter studies have been conducted using numerical examples, in order to provide guidelines for the proposed spatially local schemes, and to demonstrate the accuracy and high efficiency of the proposed method for three-dimensional soil–structure interaction problems.


      PubDate: 2015-05-03T06:08:40Z
       
  • Mitigation of railway induced ground vibration by heavy masses next to the
           track
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): A. Dijckmans , P. Coulier , J. Jiang , M.G.R. Toward , D.J. Thompson , G. Degrande , G. Lombaert
      The effectiveness of heavy masses next to the track as a measure for the reduction of railway induced ground vibration is investigated by means of numerical simulations. It is assumed that the heavy masses are placed in a continuous row along the track forming a wall. Such a continuous wall could be built as a gabion wall and also used as a noise barrier. Since the performance of mitigation measures on the transmission path strongly depends on local ground conditions, a parametric study is performed for a range of possible designs in a set of different ground types. A two-and-a-half dimensional coupled finite element–boundary element methodology is used, assuming that the geometry of the problem is uniform in the direction along the track. It is found that the heavy masses start to be effective above the mass–spring resonance frequency which is determined by the dynamic stiffness of the soil and the mass of the wall. At frequencies above this resonance frequency, masses at the soil׳s surface hinder the propagation of surface waves. It is therefore beneficial to make the footprint of the masses as large and stiff as possible. For homogeneous soil conditions, the effectiveness is nearly independent of the distance behind the wall. In the case of a layered soil with a soft top layer, the vibration reduction strongly decreases with increasing distance from the wall.


      PubDate: 2015-05-03T06:08:40Z
       
  • Liquefaction potential evaluations by energy-based method and stress-based
           method for various ground motions
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): T. Kokusho , Y. Mimori
      An energy-based liquefaction potential evaluation method (EBM) previously developed was applied to a uniform sand model shaken by seismic motions recorded at different sites during different magnitude earthquakes. It was also applied to actual liquefaction case histories in Urayasu city during the 2011 M9.0 Tohoku earthquake and in Tanno-cho during the 2003 M8.0 Tokachi-oki earthquake. In all these evaluations, the results were compared with those by the currently used stress-based method (SBM) under exactly the same seismic and geotechnical conditions. It was found that EBM yields similar results with SBM for several ground motions of recent earthquakes but has easier applicability without considering associated parameters. In Urayasu city, the two methods yielded nearly consistent results by using an appropriate coefficient in SBM for the M9.0 earthquake, though both overestimated the actual liquefaction performance, probably because effects of plasticity and aging on in situ liquefaction strength were not taken into account. In Tanno-cho, EBM could evaluate actual liquefaction performance due to a small-acceleration motion during a far-field large magnitude earthquake while SBM could not.


      PubDate: 2015-05-03T06:08:40Z
       
  • Characterisation of shear wave velocity profiles of non-uniform bi-layer
           soil deposits: Analytical evaluation and experimental validation
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): Maria Giovanna Durante , Dimitris Karamitros , Luigi Di Sarno , Stefania Sica , Colin A. Taylor , George Mylonakis , Armando Lucio Simonelli
      A crucial aspect of physical geotechnical model tests (under both 1-g and n-g conditions) is the evaluation of the initial (low-strain) stiffness of the soil layers of the sample test deposit, especially in the case of coarse materials. While for uniform soil deposits this issue can be addressed in a straightforward manner, e.g. by determining the fundamental frequency through the transfer function of an applied white-noise excitation, the problem becomes cumbersome for multi-layered deposits. After reviewing a number of available theoretical solutions, this paper illustrates a simplified yet reliable analytical procedure for determining the shear wave velocity profile (V s) in a single or bi-layer deposit, taking into account the inhomogeneity of the individual soil layers, under the hypothesis of vanishing shear modulus at ground surface. The fundamental natural frequency of the inhomogeneous bi-layer deposit is analysed using the Rayleigh quotient procedure. The associated shape function is evaluated by considering the equilibrium of the soil column under a pseudo-static lateral inertial excitation imposed at its base, accounting for both layering and inhomogeneity. A validation of the proposed method is provided by comparing numerical results obtained from both time- and frequency- domain analyses against experimental data on Leighton Buzzard sand, from a recently-completed research project conducted on the shaking table facility at BLADE Laboratory, University of Bristol (UK).


      PubDate: 2015-04-28T14:20:05Z
       
  • Estimation of liquefaction potential from dry and saturated sandy soils
           under drained constant volume cyclic simple shear loading
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): M.Murat Monkul , Cihan Gültekin , Müge Gülver , Özge Akın , Ece Eseller-Bayat
      Understanding the liquefaction mechanism of sandy soils still remains as one of the challenges in geotechnical earthquake engineering, since clean sands, silty sands and clayey sands do not necessarily show identical reactions under seismic loading. This study investigates the cyclic simple shear responses of three sandy soils: clean sand (Sile Sand 20/55), silty sand (Sile Sand 20/55 with 10% IZ silt) and clayey sand (Sile Sand 20/55 with 10% kaolin) based on many dry and saturated specimens. Drained constant volume cyclic simple shear tests on clean and silty sand specimens have shown that liquefaction potential of those soils could also be determined via dry samples. This is an important observation, since dry specimens are much easier to prepare and less time consuming compared to their saturated counterparts, as the demanding saturation process is eliminated. However, cyclic responses of dry and saturated clayey sand specimens were shown to be quite different, and therefore saturation of these specimens is still a must for liquefaction assessment. For both silt and kaolin, adding 10% fines to the base sand increased the liquefaction potential of resulting sandy soils considerably compared to the clean sand at the same void ratio. But this difference relatively decreased as the specimens became looser.


      PubDate: 2015-04-28T14:20:05Z
       
  • Bayesian analysis on earthquake magnitude related to an active fault in
           Taiwan
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): J.P. Wang , Su-Chin Chang , Yih-Min Wu , Yun Xu
      It is understood that sample size could be an issue in earthquake statistical studies, causing the best estimate being too deterministic or less representative derived from limited statistics from observation. Like many Bayesian analyses and estimates, this study shows another novel application of the Bayesian approach to earthquake engineering, using prior data to help compensate the limited observation for the target problem to estimate the magnitude of the recurring Meishan earthquake in central Taiwan. With the Bayesian algorithms developed, the Bayesian analysis suggests that the next major event induced by the Meishan fault in central Taiwan should be in M w 6.44±0.33, based on one magnitude observation of M w 6.4 from the last event, along with the prior data including fault length of 14km, rupture width of 15km, rupture area of 216km2, average displacement of 0.7m, slip rate of 6mm/yr, and five earthquake empirical models.


      PubDate: 2015-04-28T14:20:05Z
       
  • The near-field method for dynamic analysis of structures on soft soils
           including inelastic soil–structure interaction
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): M. Ghandil , F. Behnamfar
      The problem of soil–structure interaction analysis with the direct method is studied. The direct method consists of explicitly modeling the surrounding soil to bedrock and the structure resting on the soil. For the soil medium, usually the traditional equivalent linear method with a reduced shear modulus and an increased damping ratio for the soil is used. However, this method does not work in the vicinity of foundation where the soil behavior is highly nonlinear because of presence of large strains. This research proposes a modified equivalent linear method with a further reduction of the soil shear modulus in the near-field of foundation that results in validity of using the equivalent linear method throughout. For regular short, intermediate and tall structures resting on such soft soils, a series of dynamic time-history analysis is implemented using earthquake records scaled to a sample design spectrum and the nonlinear structural responses are compared for different assumptions of soil behavior including the elasto-plastic Mohr–Coulomb, the traditional equivalent linear, and the proposed modified equivalent linear method. This analysis validates the proposed method.


      PubDate: 2015-04-28T14:20:05Z
       
  • A simplified analysis model for determining the seismic response of buried
           steel pipes at strike-slip fault crossings
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): E. Uckan , B. Akbas , J. Shen , W. Rou , F. Paolacci , M. O’Rourke
      The seismic response analysis of buried pipelines at fault crossings is a complex problem requiring nonlinear 3D soil-structure and large deformation analyses. Such analyses are computationally expensive and the results are hard to evaluate. Therefore, a simple numerical model is needed for engineering and design offices to determine the seismic demand of steel pipes at fault crossings. This paper presents a simplified numerical model for buried steel pipes crossing strike-slip faults and oriented perpendicular to the fault. Two pipes with different diameter to thickness (D/t) ratios and steel grades are used in the study. The proposed model permits plastic hinge formations in the pipe due to incrementally applied fault movements, allows determination of the critical length of the pipeline and measure strains developed on the tension and compression sides in the pipe. The model also considers the effect of bending as well as axial strains due to stretching.


      PubDate: 2015-04-28T14:20:05Z
       
  • Development of an empirical correlation for predicting shear wave velocity
           of Christchurch soils from cone penetration test data
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): Christopher R. McGann , Brendon A. Bradley , Merrick L. Taylor , Liam M. Wotherspoon , Misko Cubrinovski
      Following the companion study of McGann et al. [1], seismic piezocone (SCPTu) data compiled from sites in Christchurch, New Zealand area are used with multiple linear regression to develop a Christchurch-specific empirical correlation for use in predicting soil shear wave velocities, V s , from cone penetration test (CPT) data. An appropriate regression functional form is selected through an evaluation of the residuals for regression models developed with the Christchurch SCPTu database using functional forms adopted by previous empirical correlations between V s and CPT data. An examination of how the residuals for the chosen regression form vary with the predictor variables identifies the need for non-constant depth variance in the regression model. The performance of the model is assessed through comparisons of predicted and observed V s profiles and through forward predictions with synthetic CPT data. The new CPT–V s correlation provides a method to estimate V s from CPT data that is specific to the non-gravel soils of the Christchurch region in their current state (caution should be used for western portions of the Springston Formation where SCPTu data were sparse). The correlation also enables the utilization of the large, high-density database of CPT logs ( > 15 , 000 as of 1/1/2014) in the Christchurch region for the development of both site-specific and region-wide models of surficial V s for use in site characterization and site response analysis.


      PubDate: 2015-04-28T14:20:05Z
       
  • Applicability of existing empirical shear wave velocity correlations to
           seismic cone penetration test data in Christchurch New Zealand
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): Christopher R. McGann , Brendon A. Bradley , Merrick L. Taylor , Liam M. Wotherspoon , Misko Cubrinovski
      Seismic piezocone (SCPTu) data compiled from 86 sites in the greater Christchurch, New Zealand area are used to evaluate several existing empirical correlations for predicting shear wave velocity from cone penetration test (CPT) data. It is shown that all the considered prediction models are biased towards overestimation of the shear wave velocity of the Christchurch soil deposits, demonstrating the need for a Christchurch-specific shear wave velocity prediction model (McGann et al., 2014) [1]. It is hypothesized that the unique depositional environment of the considered soils and the potential loss of soil ageing effects brought about by the 2010–2011 Canterbury earthquake sequence are the primary source of the observed prediction bias.


      PubDate: 2015-04-28T14:20:05Z
       
  • Torsional vibration of a finite cylindrical cavity in a two-layer
           transversely isotropic half-space
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): Azizollah Ardeshir-Behrestaghi , Morteza Eskandari-Ghadi , Bahram Navayi neya , Javad Vaseghi-Amiri
      The aim of this paper is to present a rigorous investigation for a two-layered transversely isotropic linear elastic half-space containing a circular cylindrical cavity of length equal to the top layer undergoing mono-harmonic ring shape shear stress applied either on the vertical cylindrical surface or on the base of the cavity. To this end, a combination of Fourier cosine integral transform for depth and Hankel integral transform for radial distance are used, which translate the boundary value problem to a singular integral equation for the shear stress comes out from the continuity of two layers. The integral equation is solved for some collocation points with a smoothed variable of distance, which is adapted with the use of a free parameter. It is shown that, although the shear stress is highly singular, it does not highly depend on this free parameter. Both the analytical and numerical results are verified with both the static isotropic and dynamic transversely isotropic homogeneous cases. In addition, some new graphical results are presented for more understanding in engineering point of view.


      PubDate: 2015-04-28T14:20:05Z
       
  • Cyclic DSS tests for the evaluation of stress densification effects in
           liquefaction assessment
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): A. Viana Da Fonseca , M. Soares , A.B. Fourie
      To evaluate the stress correction factor for the Cyclic Resistance Ratio (“CRR”) under cyclic loading with principal stress rotation, 86 Cyclic Direct Simple Shear (CDSS) tests were performed on two sands, one from Ain Beniam, in Alger, Algeria, and another from Coimbra, Portugal. These sands have distinctive grain shapes and size distributions and were tested with various relative densities and under different initial effective confining stresses. The results of the tests performed with zero initial static shear stress – therefore with the static shear stress factor K α equal to one – indicate that the values of confining stress level correction factor, K σ, as currently recommended, seem to underestimate the cyclic resistance.


      PubDate: 2015-04-28T14:20:05Z
       
  • Cyclic and post-cyclic shear behavior of low-plasticity silt with varying
           clay content
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): Shuying Wang , Ronaldo Luna , Honghua Zhao
      This paper investigates the cyclic and post-cyclic shear behavior of low-plasticity silt and the impact of additional clay content. Bentonite clay was added to the low-plasticity Mississippi River Valley (MRV) silt (PI=6) to increase the clay content of the soil. A series of triaxial tests were conducted in the laboratory to examine the shear and pore pressure behavior during and after cyclic loading. As the bentonite content in the reconstituted specimens increased, the excess pore pressure developed at a slower rate and the total excess pore pressure decreased at the end of cyclic loading. In contrast to the MRV silt, the specimens modified with bentonite experienced cyclic softening rather than initial flow liquefaction. The cyclic shear strength increased with an increase in bentonite content. The post-cyclic reconsolidation behavior was a similar to a virgin compression process, and not recompression. Adding bentonite to the MRV silt results in changes in permeability, compressibility, undrained shear strength, and initial stiffness. Additionally, the cyclic loading had a marked effect on the shear behavior of low-plasticity soil with a PI<6, but not noticeable with a PI>6. This study suggests that the behavior of the Mississippi River Valley silt changes from contractive sand-like material to clay-like behavior at a PI≈6 due to the addition of clay.


      PubDate: 2015-04-28T14:20:05Z
       
  • Seismic response of shallow circular tunnels in two-layered ground
    • Abstract: Publication date: August 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 75
      Author(s): Rui Carrilho Gomes , Fátima Gouveia , Diogo Torcato , Jaime Santos
      The effect of ground stratification on the seismic response of circular tunnels is investigated, as most practice-oriented studies consider homogeneous ground. A finite element plain-strain model of a circular tunnel cross-section embedded in a two-layered ground is used to highlight the influence of stratification on the tunnel׳s seismic response. The layers interface was placed at the crown, centre and invert level. It is proved that ground stratification has an important role in the lining seismic forces. When the tunnel is fully embedded in one of the layers, the seismic lining forces may vary significantly in comparison with the single-layer case. If the tunnel intercepts both layers, maximum lining forces aggravation occurs when the lower layer is very stiff.


      PubDate: 2015-04-28T14:20:05Z
       
  • CFRP composite retrofitting effect on the dynamic characteristics of arch
           dams
    • Abstract: Publication date: July 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 74
      Author(s): Ahmet Can Altunişik , Murat Günaydin , Barış Sevim , Alemdar Bayraktar , Süleyman Adanur
      The purpose of this study is to investigate the effect of retrofitting dynamic characteristics of a damaged laboratory arch dam model, subsequently repaired with high-strength structural mortar and strengthened with composite carbon fiber reinforced polymer. This study constructed in laboratory conditions is a prototype arch dam–reservoir–foundation model. Five test cases of ambient vibration on the arch dam model illustrate the changes in dynamic characteristics: natural frequency, mode shape, and damping ratio, before and after retrofitting. The ambient vibration tests collected data from the dam body during vibrations by natural excitations which provided small impacts and response signals from sensitivity accelerometers placed at crest points. Enhanced Frequency Domain Decomposition Method in the frequency domain extracts the experimental dynamic characteristics. At the end of the study, experimentally identified dynamic characteristics obtained from all test cases have been compared with each other. Apparently, after the retrofitting, the natural frequencies of the dam body increased considerably, demonstrating that the retrofitting, including repairing and strengthening is very effective on the flashback of initial dynamic characteristics.


      PubDate: 2015-04-28T14:20:05Z
       
  • Local ground effects in near-field and far-field areas on seismically
           protected buildings
    • Abstract: Publication date: July 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 74
      Author(s): Dora Foti
      This paper presents a 2-D numerical study on the nonlinear seismic response of buildings equipped with two types of energy dissipators, which dissipate energy activating two different mechanisms. Three types of reinforced concrete buildings with 3, 7 and 15 stories, respectively representative of short, medium and long period ranges, are considered. Dissipators are placed on steel diagonal braces at all the floors; their sliding threshold (or yielding) forces are taken as 100% of those generated by the equivalent static lateral forces recommended by EC8 for a ductile moment resisting frame. The input consists of six recorded earthquakes, 3 representatives of near-field earthquakes and 3 representatives of far-field earthquakes. Each input is considered once from the bedrock and once filtered by a common ground with several layers of different thicknesses. The responses of the buildings are discussed and compared emphasizing the filtering effects produced by the ground.


      PubDate: 2015-04-28T14:20:05Z
       
  • Preferred frequencies for coupling of seismic waves and vibrating tall
           buildings
    • Abstract: Publication date: July 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 74
      Author(s): Darko Volkov , Sergey Zheltukhin
      We study a model for the so-called “city effect” in which an earthquake can be locally enhanced by the collective response of tall buildings in a large city. We use a set of equations coupling vibrations in buildings to motion under the ground. These equations were previously studied exclusively in the case of a finite set of identical, equally spaced, buildings. These two restrictions are lifted in this paper. We may now simulate geometries involving infinitely many buildings as long as an initial pattern of buildings is repeated. Our new method using periodic domains and periodic Green׳s functions yields much faster computations. This is the main reason why we are now able to study systems of buildings of variable height, mass, and rigidity. We show how solving for the wavenumber in a non-linear equation involving the integral of a function solution to an adequate integral equation, we are able to find resonant frequencies coupling seismic waves and vibrating tall buildings. Interestingly, in the case of non-identical buildings, our simulations indicate that the response to this coupling phenomenon may differ drastically from one building to another.


      PubDate: 2015-04-28T14:20:05Z
       
  • Seismic analyses of a RCC building under mainshock–aftershock
           seismic sequences
    • Abstract: Publication date: July 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 74
      Author(s): Chang-Hai Zhai , Zhi Zheng , Shuang Li , Li-Li Xie
      A large mainshock may trigger numerous aftershocks within a short period, and nuclear power plant (NPP) structures have the probability to be exposed to mainshock–aftershock seismic sequences. However, the researchers focused on seismic analyses of reinforced concrete containment (RCC) buildings under only mainshocks. The aim of this paper is to thoroughly investigate the dynamic responses of a RCC building under mainshock–aftershock seismic sequences. For that purpose, 10 as-recorded mainshock–aftershock seismic sequences with two horizontal components are considered in this study, and a typical three-dimensional RCC model subjected to the selected as-recorded seismic sequences is established. Peak ground accelerations (PGAs) of mainshocks equal to 0.3g (safe shutdown earthquake load-SSE load) are considered in this paper. The results indicate that aftershocks have a significant effect on the responses of the RCC in terms of maximum top accelerations, maximum top displacements and accumulated damage. Furthermore, in order to preserve the RCC from large damage under repeated earthquakes, local damage and global damage indices are suggested as limitations under only mainshocks.


      PubDate: 2015-04-28T14:20:05Z
       
  • Modelling of shear keys in bridge structures under seismic loads
    • Abstract: Publication date: July 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 74
      Author(s): Kaiming Bi , Hong Hao
      Shear keys are used in the bridge abutments and piers to provide transverse restraints for bridge superstructures. Owing to the relatively small dimensions compared to the main bridge components (girders, piers, abutments, piles), shear keys are normally regarded as secondary component of a bridge structure, and their influences on bridge seismic responses are normally neglected. In reality, shear keys are designed to restrain the lateral displacements of bridge girders, which will affect the transverse response of the bridge deck, thus influence the overall structural responses. To study the influences of shear keys on bridge responses to seismic ground excitations, this paper performs numerical simulations of the seismic responses of a two-span simply-supported bridge model without or with shear keys in the abutments and the central pier. A detailed 3D finite element (FE) model is developed by using the explicit FE code LS-DYNA. The bridge components including bridge girders, piers, abutments, bearings, shear keys and reinforcement bars are included in the model. The non-linear material behaviour including the strain rate effects of concrete and steel rebar are considered. The seismic responses of bridge structures without and with shear keys subjected to bi-axial spatially varying horizontal ground motions are calculated and compared. The failure mode and damage mechanism of shear keys are discussed in detail. Numerical results show that shear keys restrain transverse movements of bridge decks, which influence the torsional–lateral responses of the decks under bi-axial spatially varying ground excitations; neglecting shear keys in bridge response analysis may lead to inaccurate predictions of seismic responses of bridge structures.


      PubDate: 2015-04-28T14:20:05Z
       
  • Nonlinear stochastic seismic analysis of buried pipeline systems
    • Abstract: Publication date: July 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 74
      Author(s): Wei Liu , Qianwei Sun , Huiquan Miao , Jie Li
      In this paper, a nonlinear stochastic seismic analysis program for buried pipeline systems is developed on the basis of a probability density evolution method (PDEM). A finite element model of buried pipeline systems subjected to seismic wave propagation is established. The pipelines in this model are simulated by 2D beam elements. The soil surrounding the pipelines is simulated by nonlinear distributed springs and linear distributed springs along the axial and horizontal directions, respectively. The joints between the segmented pipes are simulated by nonlinear concentrated springs. Thereafter, by considering the basic random variables of ground motion and soil, the PDEM is employed to capture the stochastic seismic responses of pipeline systems. Meanwhile, a physically based method is employed to simulate the random ground motion field for the area where the pipeline systems are located. Finally, a numerical example is investigated to validate the proposed program.


      PubDate: 2015-04-28T14:20:05Z
       
  • Algorithm design of an hybrid system embedding influence of soil for
           dynamic vibration control
    • Abstract: Publication date: July 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 74
      Author(s): A. Baratta , I. Corbi , O. Corbi
      The paper outlines an approach for improving the effectiveness and reliability of base isolation devices in civil engineering structures that undergo exceptional dynamic conditions. The strategy consists of designing the passive device in such a way to take into account the not-negligible soil–structure interaction effects. At this stage, the isolator is, then, designed in such a way to be optimally tuned on the basis of the characteristics of the structure and of the soil at the site. Anyway limits intrinsic in the effectiveness of the passive device cannot be completely overcome even when embedding in the design the influence of the soil filtering on the structural response. Therefore, at the second stage, an active vibration device is coupled to the basic isolator, which is, in turn, optimally designed for minimizing the structural response and control costs. The overall presented approach definitively produces an effective hybrid control base isolation, already optimized for the specific structure and soil in its passive component, and able to concentrate the active control effort only on the frequency ranges where it is required.


      PubDate: 2015-04-28T14:20:05Z
       
  • A comparison of material damping measurements in resonant column using the
           steady-state and free-vibration decay methods
    • Abstract: Publication date: July 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 74
      Author(s): Kostas Senetakis , Anastasios Anastasiadis , Kyriazis Pitilakis
      The study reports results associated with the small to medium strain range material damping of quartz sand. The experiments were conducted in a fixed-free type resonant column and the samples were subjected to torsional mode of vibration at their first natural frequency. A comparison between the derived damping values using two different methods is presented: the steady-state vibration method (SSV) and the free-vibration decay method (FVD). Within the scatter of the data the two different methods in measuring material damping provided comparable results with a scatter, in most cases, of less than ±15% for the working strain range of the resonant column method. The damping values derived from the FVD and SSV methods were also compared with proposed models in the literature by means of stiffness degradation–damping increase correlation.


      PubDate: 2015-04-28T14:20:05Z
       
  • An analytical model to predict the natural frequency of offshore wind
           turbines on three-spring flexible foundations using two different beam
           models
    • Abstract: Publication date: July 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 74
      Author(s): L. Arany , S. Bhattacharya , S. Adhikari , S.J. Hogan , J.H.G. Macdonald
      In this study an analytical model of offshore wind turbines (OWTs) supported on flexible foundation is presented to provide a fast and reasonably accurate natural frequency estimation suitable for preliminary design or verification of Finite Element calculations. Previous research modelled the problem using Euler–Bernoulli beam model where the foundation is represented by two springs (lateral and rotational). In contrast, this study improves on previous efforts by incorporating a cross-coupling stiffness thereby modelling the foundation using three springs. Furthermore, this study also derives the natural frequency using Timoshenko beam model by including rotary inertia and shear deformation. The results of the proposed model are also compared with measured values of the natural frequency of four OWTs obtained from the literature. The results show that the Timoshenko beam model does not improve the results significantly and the slender beam assumption may be sufficient. The cross-coupling spring term has a significant effect on the natural frequency therefore needs to be included in the analysis. The model predicts the natural frequency of existing turbines with reasonable accuracy.


      PubDate: 2015-04-28T14:20:05Z
       
  • Editorial Board / Aims and Scope
    • Abstract: Publication date: June 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 73




      PubDate: 2015-04-28T14:20:05Z
       
  • Improved seismic risk estimation for Bucharest, based on multiple hazard
           scenarios and analytical methods
    • Abstract: Publication date: June 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 73
      Author(s): D. Toma-Danila , C. Zulfikar , E.F. Manea , C.O. Cioflan
      Bucharest, capital of Romania, is one of the most exposed big cities in Europe to seismic damage, due to the intermediate-depth earthquakes in the Vrancea region, to the vulnerable building stock and local soil conditions. This paper tries to answer very important questions related to the seismic risk at city scale that were not yet adequately answered. First, we analyze and highlight the bottlenecks of previous risk-related studies. Based on new researches in the hazard of Bucharest (recent microzonation map and ground-motion prediction equations, reprocessed real recorded data) and in vulnerability assessment (analytical methods, earthquake loss estimation software like SELENA and ELER, the recently implemented Near Real-Time System for Estimating the Seismic Damage in Romania) we provide an improved estimation of the number of buildings and population that could be affected, for different earthquake scenarios. A new method for enhancing the spatial resolution of the building stock data is used successfully.


      PubDate: 2015-04-28T14:20:05Z
       
  • Determination of mean shear wave velocity to 30m depth for site
           classification using shallow depth shear wave velocity profile in Korea
    • Abstract: Publication date: June 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 73
      Author(s): Chang-Guk Sun
      The mean shear wave velocity to a depth of 30m (V S 30), established in the western United States, is the current site classification criterion for determining the seismic design ground motion, taking site amplification potential account into. To evaluate V S 30 at a site, a shear wave velocity (V S ) profile extending to a depth of at least 30m must be acquired using in situ seismic tests. In many cases, however, the obtained V S profile does not extend to a depth of 30m due to unfavorable field conditions and limitations of testing techniques. In this study, V S 30 and the mean shear wave velocity to depths less than 30m (V S Ds) were calculated using V S profiles of more than 30m obtained by seismic tests at 72 sites in Korea, and the correlation between V S 30 and V S Ds was drawn based on the computed mean V S data. Additionally, a method for extrapolating the V S profile from shallow depths to 30m and bedrock was developed by building a shape curve based on the average data of all V S profiles. These two methods of extrapolating V S 30 from shallow V S profiles, using V S Ds and a shape curve, resulted in less bias than the simple method in which the lowermost V S value obtained is extended to the depth of 30m. These two extrapolation methods are useful for V S profiles extending to depths of at least 10m. Furthermore, the shape curve method developed in this study may be useful in the western United States as well as in Korea.


      PubDate: 2015-04-28T14:20:05Z
       
  • The influence of using CFRP wraps on performance of buried steel pipelines
           under permanent ground deformations
    • Abstract: Publication date: June 2015
      Source:Soil Dynamics and Earthquake Engineering, Volume 73
      Author(s): M. Mokhtari , A. Alavi Nia
      In this study, using FRP wraps to reinforce buried steel pipelines under permanent ground deformations is investigated. For this purpose, carbon/epoxy composite wrap was used on API 5L grade X65 pipeline which is the typical material for oil and gas transportation pipelines. Mechanical behavior of the pipelines under strike-slip faulting was studied using nonlinear finite element code ABAQUS. The pipeline was supposed to be perpendicular to the fault plane. Proper performance criteria were used to determine critical fault displacements. According to defined performance criteria, critical fault displacements for different diameter to thickness ratios, various composite wrap thicknesses, and for both non-pressurized and pressurized pipelines were determined. Percentages of increase in critical fault displacements compared to non-wrapped conditions were calculated. In some pressurized pipelines, increasing strain in the ruptured area of composite wrap on the pipeline led pipeline to rupture at ultimate tensile strain of the pipe material. Results indicate that using 1-mm-thick composite wrap for non-pressurized pipelines leads critical fault displacement to increase about 100%. In addition, by increasing the thickness of composite wrap, the value of critical fault displacement increases significantly, so that applying composite wraps with thicknesses of 1 and 10mm on pressurized pipelines with diameter to thickness ratio of 144 caused critical fault displacement to increase by 154% and 892%, respectively. According to results of this research, using FRP wraps to reinforce buried steel pipelines under permanent ground deformations is recommended.


      PubDate: 2015-04-28T14:20:05Z
       
 
 
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