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Journal Cover Soil Dynamics and Earthquake Engineering
  [SJR: 1.482]   [H-I: 45]   [11 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0267-7261
   Published by Elsevier Homepage  [2969 journals]
  • A unified model for estimating the in-situ small strain shear modulus of
           clays, silts, sands, and gravels
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Brian D. Carlton, Juan M. Pestana
      This paper proposes a unified model to estimate the in-situ small strain shear modulus of clays, silts, sands, and gravels based on commonly available index properties of soils. We developed a model to predict the laboratory small strain shear modulus (G max,lab) using a mixed effects regression of a database that contains 1680 tests on 331 different soils. The proposed model includes the effect of void ratio, effective confining stress and overconsolidation ratio as well as plasticity index, fines content, and coefficient of uniformity. We compiled a second database to estimate the in-situ small strain shear modulus (G max,in-situ) from laboratory (G max,lab) measurements. This study validated and compared the resulting model with other existing models using a third database of measured G max,in-situ values. The residuals of the proposed model had a mean and median closer to zero and the smallest standard deviation of all the models considered. By including a statistical description of the residuals, this work allows uncertainty of the small strain shear modulus to be included in probabilistic studies.


      PubDate: 2016-07-27T08:49:17Z
       
  • Optimum lateral load distribution for seismic design of nonlinear
           shear-buildings considering soil-structure interaction
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Behnoud Ganjavi, Iman Hajirasouliha, Ali Bolourchi
      The lateral load distributions specified by seismic design provisions are primarily based on elastic behaviour of fixed-base structures without considering the effects of soil-structure-interaction (SSI). Consequently, such load patterns may not be suitable for seismic design of non-linear flexible-base structures. In this paper, a practical optimisation technique is introduced to obtain optimum seismic design loads for non-linear shear-buildings on soft soils based on the concept of uniform damage distribution. SSI effects are taken into account by using the cone model. Over 30,000 optimum load patterns are obtained for 21 earthquake excitations recorded on soft soils to investigate the effects of fundamental period of the structure, number of stories, ductility demand, earthquake excitation, damping ratio, damping model, structural post yield behaviour, soil flexibility and structural aspect ratio on the optimum load patterns. The results indicate that the proposed optimum load patterns can significantly improve the seismic performance of flexible-base buildings on soft soils.


      PubDate: 2016-07-27T08:49:17Z
       
  • A study of the reduction of ground vibrations by an active generator
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Aneta Herbut
      This paper presents the concept of using an additional generator to prevent ground vibrations. A linear, transversally isotropic three dimensional half-space with the hysteretic damping model, acted upon by a harmonic vertical excitation is assumed. Equations of motion for the transversally isotropic ground model with the absorbing boundary conditions are presented and numerically integrated using FlexPDE software, based on the finite element method. The efficiency of the solution is analysed in terms of reducing the vertical and horizontal components of ground surface vibrations. Results in the form of a dimensionless amplitude reduction factor are presented for four different locations of a generator. The influence of the soil parameters and layers locations on the additional generator's efficiency is investigated. The vibration reduction efficiency in a four-story building is also presented.


      PubDate: 2016-07-27T08:49:17Z
       
  • Centrifuge modelling of flexible retaining walls subjected to dynamic
           loading
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Michele Tricarico, Gopal Santana Phani Madabhushi, Stefano Aversa
      This paper outlines the results of an experimental program carried out on centrifuge models of cantilevered and propped retaining walls embedded in saturated sand. The main aim of the paper is to investigate the dynamic response of these structures when the foundation soil is saturated by measuring the accelerations and pore pressures in the soil, displacements and bending moment of the walls. A comparison among tests with different geometrical configurations and relative density of the soil is presented. The centrifuge models were subjected to dynamic loading in the form of sinusoidal accelerations applied at the base of the models. This paper also presents data from pressure sensors used to measure total earth pressure on the walls. Furthermore, these results are compared with previous dynamic centrifuge tests on flexible retaining walls in dry sand.


      PubDate: 2016-07-27T08:49:17Z
       
  • Seismic microzoning from synthetic ground motion earthquake scenarios
           parameters: The case study of the city of Catania (Italy)
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): F. Castelli, A. Cavallaro, S. Grasso, V. Lentini
      The city of Catania (Italy) in the South-Eastern Sicily has been affected in past times by several destroying earthquakes with high values of estimated magnitude. The seismogenic area to the south of Volcano Etna, known as Iblean Area, is placed between the African and the Euro-Asiatic plates on the west of the Ibleo-Maltese escarpment, to the south of the Graben of the Sicilian channel and on the east of the overlapping front of Gela. Basing on the seismic history of Catania, the following earthquake scenarios have been considered: the “Val di Noto” earthquake of January 11, 1693 (with intensity X-XI on MCS scale, magnitude MW=7.41 and epicentral distance of about 13km); the “Etna” earthquake of February 20, 1818 (with intensity IX on MCS scale, magnitude MW=6.23 and epicentral distance of about 10km). The soil response analysis at the surface, in terms of time history and response spectra, has been obtained by 1-D equivalent linear models for about 1200 borings location available in the data-bank of the central area of Catania of about 50km2, using deterministic design scenario earthquakes as input at the conventional bedrock. Seismic microzoning maps of the city of Catania have been obtained in terms of different peak ground acceleration at the surface and in terms of amplification ratios for given values of frequency.


      PubDate: 2016-07-27T08:49:17Z
       
  • Modal identification of a centrifuge soil model using subspace state space
           method
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): H. Soltani, K.K. Muraleetharan, T. Runolfsson
      In this paper, modal parameters of a layered soil system comprising of a soft clay layer overlying a dense sand layer are identified from accelerometer recordings in a centrifuge test. For the first time, the subspace state space system identification (4SID) method was employed to identify the natural frequencies, damping ratios, and complex valued mode shapes while considering the non-proportional damping in a soil system. A brief review of system identification concepts needed for application of the 4SID techniques to structural modal identification is provided in the paper. The identified natural frequencies were validated against those estimated by transfer function spectra. The computed normal mode shapes were compared with closed-form solutions obtained from the one-dimensional shear wave propagation equation. The identified modal parameters were then employed to synthesize state space prediction models which were subsequently used to simulate the soil response to three successive base motions. The identified models captured acceleration time-histories and corresponding Fourier spectra reasonably well in the small and moderate shaking events. In the stronger third shaking event, the model performed well at greater soil depths, but was less accurate near the surface where nonlinearities dominated.


      PubDate: 2016-07-19T08:31:08Z
       
  • Cyclic behavior and pore pressure generation in sands with laponite, a
           super-plastic nanoparticle
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Felipe Ochoa-Cornejo, Antonio Bobet, Cliff T. Johnston, Marika Santagata, Joseph V. Sinfield
      The paper examines the effect of the presence of small percentages (1–5%) by dry mass of the sand of laponite – a synthetic nanoclay with plasticity index exceeding 1000% – on the cyclic response of sand with relative density in the 15–25% range. The work is based on cyclic triaxial tests performed on specimens prepared pluviating sand and laponite under dry conditions and then permeated with water. 1% laponite impacts all stages of the cyclic tests, from the response during the first loading cycle to liquefaction, increasing the cyclic resistance. Further benefits are observed with a longer pre-shear aging period or higher dosages (3–5%) of laponite. The observed behavior is associated with reduced mobility of the sand particles during cyclic loading, which can be ascribed to two mechanisms: (1) bonding/bridging at the particle contacts due to the charged laponite fines which are attracted to the sand grains; and (2) formation of a pore fluid with solid like properties. The first appears to control the behavior with 1% laponite, while it is proposed that the second is responsible for the response with higher dosages of laponite. The results presented provide new insight into the effects of high plastic fines on the cyclic response of sands, the “extreme” effects of the plasticity of the fines, and are significant in light of the possible use of laponite for liquefaction mitigation, an idea first put forth by the authors.


      PubDate: 2016-07-19T08:31:08Z
       
  • Wave propagation of buried spherical SH-, P1-, P2- and SV-waves in a
           layered poroelastic half-space
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Zhenning Ba, Jianwen Liang, Vincent W. Lee
      Few studies have investigated the wave propagation of spherical sources in a layered half-space. In this paper, based on Biot's theory of poroelastic media, the exact anti-axisymmetric (cylindrical SH-waves) and axisymmetric (cylindrical P1-P2-SV waves) stiffness matrices for a layered poroelastic half-space are derived. Then the dynamic responses due to buried spherical SH-, P1-, P2- and SV-waves in a layered poroelastic half-space are studied by using the direct stiffness method combined with the Hankel transform. The present solutions are in good agreements with those in a uniform pure elastic half-space as well as a uniform poroelastic half-space. These solutions have the advantages that all of the parameters in the solutions have explicit physical meanings and the thickness of discrete layers does not affect the precision of calculation; thus, the presented formulations are very convenient for engineering applications. Numerical calculations are performed in both the frequency and time domains by taking buried spherical SH-, P1- and SV- waves in a uniform poroelastic half-space and in a single poroelastic layer over a poroelastic half-space as examples. The numerical results show that wave propagation of spherical sources in a layered half-space can be significantly different from that in a uniform half-space; the dynamic responses are highly dependent on the saturated parameters, vibration frequency and the surface drained condition; the presence of the underlying half-space makes the time histories of the dynamic responses in a single layered half-space much more complicated with much longer duration.


      PubDate: 2016-07-09T08:02:08Z
       
  • Seismic response analysis in the southern part of the historic centre of
           the City of L’Aquila (Italy)
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): A. Ferraro, S. Grasso, M. Maugeri, F. Totani
      This paper deals in the 2011 extensive site investigation by means of boreholes up to a depth of 80m, Down-Hole (D-H) tests, Seismic Dilatometer Marchetti Tests (SDMT), Multichannel Analysis of Surface Waves (MASW) tests in the area of via XX Settembre of the city centre of L’Aquila (Italy), to obtain a detailed geotechnical model. Results of site investigations showed a marked variability of shear wave velocity Vs profiles, especially in the upper 5–10m, where different soil types are commonly encountered, all characterised by low values of Vs. In this paper the main features of the April 6, 2009 L’Aquila Earthquake (ML=5.8; MW=6.3) are also discussed. The earthquake caused 308 casualties and heavy damage in the city of L’Aquila and in the surroundings villages. Some accelerometric stations were located across the Aterno River Valley, while only one station (namely AQK) was located in the city centre of L’Aquila. The peak acceleration values ranged from 0.35g recorded in the city centre to 0.65g recorded in the middle Aterno valley. The recorded time histories were characterised by short durations and high peak accelerations both in the horizontal and in the vertical directions. The area of via XX Settembre (southern part of the historic centre of the city of L’Aquila) was severely damaged by the earthquake. This area, located at a very short distance from the city centre, includes also some reinforced concrete frame buildings, mostly 5–7 storey high, built between 1950 and 1965. Old masonry buildings and some of these r.c. buildings collapsed or suffered severe damage due to the main shock, causing several tens of victims. The peculiar subsoil conditions locally detected down to about 40m depths in this area include fine-grained soils interposed within, or placed above, “Brecce dell’Aquila” (typical of L’Aquila) and man-made fills. Low and variable shear wave velocity VS values in the upper portion of the subsoil have locally originated major amplification of the ground motion during the main shock. Therefore the paper deals also in specific one-dimensional numerical seismic response analyses performed. Significant amplification effects related to local subsoil conditions, bigger than the amplification factors given by the Italian Building Code NTC 2008, have been discovered by the seismic response analyses carried out at the site. The results of soil response analyses were compared with the occurred damage in the area.


      PubDate: 2016-07-09T08:02:08Z
       
  • Effects of wave passage on torsional response of symmetric buildings
           subjected to near-fault pulse-like ground motions
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Yenan Cao, Kristel C. Meza-Fajardo, George P. Mavroeidis, Apostolos S. Papageorgiou
      This article investigates the effects of wave passage on the torsional response of elastic buildings in the near-fault region. The model of the soil-foundation-structure system is a symmetric cylinder placed on a rigid circular foundation supported on an elastic halfspace. The idealized model is subjected to obliquely incident plane SH waves simulating the action of near-fault pulse-like motions. The response of the structure is assessed in terms of the relative twist between the top and the base of the superstructure. A parametric analysis of the maximum relative twist as a function of the input parameters of the seismic excitation and soil-foundation-structure system is performed to identify the parameters that control the torsional response of buildings due to wave passage in the near-fault region. It is shown that the torsional response is most sensitive to a key parameter of the near-fault ground motion referred to as “pulse period”. Specifically, large rotations are observed when the pulse period is close to the torsional period of the structure. It is also demonstrated that the wave passage effects are controlled by the wave apparent velocity, rather than the local site conditions. Furthermore, broadband near-fault ground motions from three hypothetical earthquakes of different magnitude are generated, and the torsional responses due to the simplified pulse-like and broadband ground motions are compared against each other. The results show that the simplified pulse model that describes the coherent seismic radiation is able to represent the main features of the near-fault ground motions that cause large torsional response. The maximum relative twist at resonance is found to be ~ 10 − 3 rad, a value that is consistent with the upper bound of rotations in structures reported in the literature.


      PubDate: 2016-06-30T08:02:10Z
       
  • Numerical investigation of the response of the Yele rockfill dam during
           the 2008 Wenchuan earthquake
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Bo Han, Lidija Zdravkovic, Stavroula Kontoe, David M.G. Taborda
      In this paper the seismic response of a well-documented Chinese rockfill dam, Yele dam, is simulated and investigated employing the dynamic hydro-mechanically (HM) coupled finite element (FE) method. The objective of the study is to firstly validate the numerical model for static and dynamic analyses of rockfill dams against the unique monitoring data on the Yele dam recorded before and during the Wenchuan earthquake. The initial stress state of the dynamic analysis is reproduced by simulating the geological history of the dam foundation, the dam construction and the reservoir impounding. Subsequently, the predicted seismic response of the Yele dam is analysed, in terms of the deformed shape, crest settlements and acceleration distribution pattern, in order to understand its seismic behaviour, assess its seismic safety and provide indication for the application of any potential reinforcement measures. The results show that the predicted seismic deformation of the Yele dam is in agreement with field observations that suggested that the dam operated safely during the Wenchuan earthquake. Finally, parametric studies are conducted to explore the impact of two factors on the seismic response of rockfill dams, i.e. the permeability of materials comprising the dam body and the vertical ground motion.


      PubDate: 2016-06-30T08:02:10Z
       
  • Small-strain stiffness of sand subjected to stress anisotropy
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Meghdad Payan, Arman Khoshghalb, Kostas Senetakis, Nasser Khalili
      Stiffness of soils at small strains expressed through the small-strain shear modulus is critical for the evaluation of deformations of geo-structures subjected to a variety of stress states. While most of the previous studies of small-strain shear modulus of sands have focused on the isotropic stress state, there exist innumerable situations in geotechnical engineering in which the soil is under an anisotropic stress state. In this study, the influence of stress anisotropy on the small-strain shear modulus ( G max ) of sands is evaluated using the results of a comprehensive set of bender element tests conducted on saturated sand samples under isotropic and anisotropic loading conditions. It is shown that the small-strain shear moduli of sands under anisotropic loading conditions are greater in magnitude than those subjected to isotropic stress states at a given mean effective stress. It is also shown that the influence of stress anisotropy on the small-strain shear modulus of sands is more pronounced for sands with irregular in shape grains and wider grain size distribution in comparison to uniform sands of relatively rounded and spherical grains. Based on the experimental results, a new G max model is developed which incorporates the contribution of grain size characteristics and particle shape in the prediction of the small-strain shear modulus of sands subjected to stress anisotropy.


      PubDate: 2016-06-30T08:02:10Z
       
  • 2-D soil-structure interaction in time domain by the SBFEM and two
           non-linear soil models
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Hossein Rahnema, Sassan Mohasseb, Behtash JavidSharifi
      Effects of soil-structure interaction (SSI) have proven to be of more importance than to be ignored. Quite a few methods of modeling and analysis exist to anticipate the real behavior of the structure when placed on flexible soil rather than on rigid ground surface. Yet, how to model the soil needs to be inspected carefully since probable deformations of soil may be at times far from predicted. In this study a newly formed approach is inspected to suggest possible solutions to shortcomings of conventional ones, compare two non-linear soil models, and implement strengths of newer methods. The soil-structure system is modeled and analyzed once directly with the UCSD soil model and then compared with non-linear sub-structuring method with the UCD model. Analyzes are performed in the time domain for both cases. The soil is supposed to be comprised of sands with various density values. The Loma-Prieta earthquake record (Loma-Prieta, 1989) is used to carry out time domain analyzes and capture structural responses. The interactional forces exerted to the near-field soil, which account for the interaction between these two media as well as the radiation damping of the infinite half-space, have replaced the earthquake motion and the far-field has accordingly been truncated out. The non-linear near-field soil-structure system has then been dynamically analyzed. Force outputs reveal a decrease when elastoplastic SSI is considered; while displacement amplitudes are found to be greater for cases not involving SSI, or involving elastic SSI. Changing the applied constitutive model for the soil as well as sand density from loose to dense manifests changes in responses. As the soil gets denser, the SSI behavior gets closer to that of the elastic case. Contrary to the sub-structuring method which usually, and conventionally, assumes linear elastic behavior for the soil-structure system, direct modeling may predict non-linear responses of the system and effects of the structure′s being placed upon an inelastic environment.
      Graphical abstract image

      PubDate: 2016-06-30T08:02:10Z
       
  • Centrifuge modeling of batter pile foundations under earthquake excitation
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Zheng Li, Sandra Escoffier, Panagiotis Kotronis
      Although batter pile foundations are widely used in civil engineering structures, their behavior under seismic loadings is not yet thoroughly understood. This paper provides insights about the differences in the behavior of batter and vertical piles under seismic soil-pile-superstructure interaction. An experimental dynamic centrifuge program is presented, where the influences of the base shaking signal and the height of the gravity center of the superstructure are investigated. Various seismic responses are analyzed (displacement and rotation of the pile cap, total shear force at the pile cap level, overturning moment, residual bending moment, total bending moment and axial forces in piles). It is found that in certain cases batter piles play a beneficial role on the seismic behavior of the pile foundation system. The performance of batter piles depends not only on the characteristics of the earthquakes (frequency content and amplitude) but also on the type of superstructures they support. This novel experimental work provides a new experimental database to better understand the behavior of batter pile foundations in seismic regions.


      PubDate: 2016-06-30T08:02:10Z
       
  • The effect of fines plasticity on monotonic undrained shear strength and
           liquefaction resistance of sands
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Anthi I. Papadopoulou, Theodora M. Tika
      The paper presents results of an investigation into the effects of fines plasticity on the undrained monotonic and cyclic response of sands. Monotonic and cyclic triaxial tests on mixtures of sand with 5% and 15% fines content were performed. Non-plastic and plastic fines of varying plasticity were used. At a given fines content, confining effective stress and void ratio, the results show that the undrained shear strength and cyclic resistance decrease with increasing plasticity index of fines up to a threshold value. Above this threshold value, the undrained shear strength and cyclic resistance increase with increasing plasticity index of fines. This pattern of behaviour was also reflected in the excess pore water pressure rise during both monotonic and cyclic loading. The mechanism controlling the behaviour of sands with fines and the implications of the test results to the engineering practice are finally discussed.


      PubDate: 2016-06-30T08:02:10Z
       
  • Finite element simulations of wave propagation in soils using a
           Viscoelastic model
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Z. Cheng, E.C. Leong
      Wave propagation in soil is dependent on both the stiffness and the material damping of the soil. While some researchers have performed finite element modelling of resonant column tests and wave propagation in soil, most do not describe the methodology in detail and there is little or no verification of the correctness of the model. Viscoelastic model has been used to model wave propagation in soil. However, the determination of the parameters in the viscoelastic model is complicated and the parameters may not be related to the soil properties. This paper presents a simplified viscoelastic model with soil parameters obtainable from advanced geotechnical testing to simulate wave propagation in soil medium taking into account of material damping. The viscoelastic material model was first calibrated by replicating torsional, longitudinal and flexural modes resonant column tests. The relationships between the parameters of the simplified viscoelastic model and their corresponding stiffness and damping properties were investigated. An equation was proposed to correlate the decay constant used in the simplified viscoelastic model and the material damping ratio obtained through the application of the logarithmic decrement method on the modelled resonant column test results. The simplified viscoelastic model was then evaluated by modelling wave propagation in a semi-infinite medium. Results indicated that the viscoelastic model with parameters as proposed in this paper is able to model wave propagation in soils.


      PubDate: 2016-06-30T08:02:10Z
       
  • Assessment of capacity design of columns in steel moment resisting frames
           with viscous dampers
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Theodore L. Karavasilis
      Previous research showed that steel moment-resisting frames (MRFs) with viscous dampers may experience column plastic hinges under strong earthquakes and highlighted the need to further assess the efficiency of capacity design rules. To partially address this need, three alternatives of a prototype building having five, 10 and 20 stories are designed according to Eurocode 8 using either steel MRFs or steel MRFs with dampers. Incremental dynamic analysis (IDA) is conducted for all MRFs and their collapse resistance and plastic mechanism is evaluated. The results show that steel MRFs with dampers are prone to column plastic hinging in comparison to steel MRFs. The steel MRFs with dampers are then iteratively re-designed with stricter capacity design rules to achieve a plastic mechanism that is approximately similar to that of steel MRFs. The performance of these re-designed steel MRFs with dampers indicates, that overall, enforcement of stricter capacity design rules for columns is not justified neither from a collapse resistance or a reparability perspective.


      PubDate: 2016-06-30T08:02:10Z
       
  • Study on the effects of hydrodynamic pressure on the dynamic stresses in
           slabs of high CFRD based on the scaled boundary finite-element method
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): He Xu, Degao Zou, Xianjing Kong, Zhiqiang Hu
      As the anti-seepage bodies in concrete-faced rockfill dams (CFRDs), face slabs play a vital role in ensuring dam reliability; thus, the stresses acting on face slabs should be analysed in detail. Considering the importance of the hydrodynamic pressure on high CFRD, the hydrodynamic pressure should be calculated with accurate methods when assessing the safety of high (approximately 300m) CFRDs in strong ground motion zones. The principal objective of this paper is to investigate the effects of hydrodynamic pressure on the face slab response of a 300m high CFRD under seismic loads in different directions. A dynamic coupling method for the modelling of CFRD-reservoir systems based on an approach combining the finite-element method (FEM) and the scaled boundary finite-element method (SBFEM) is developed. The hydrodynamic pressure of an incompressible fluid, based on a semi-analytical SBFEM approach, is expressed in the form of a full added-mass matrix. Moreover, the distribution of the hydrodynamic pressure and the mechanism by which it influences the dynamic stresses in the slabs are investigated. It is revealed that hydrodynamic pressure influences the dynamic stress in face slabs through the frictional force between the cushion and the slabs and cannot be neglected in the dynamic analysis of a high CFRD.


      PubDate: 2016-06-30T08:02:10Z
       
  • On wave propagation in gradient poroelasticity
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): V.D. Smyrlis, I.P. Pegios, S. Papargyri-Beskou
      Using the governing equations of motion of a fluid- saturated poroelastic medium including micro-stiffness (for the solid and the fluid) and micro-inertia (for the solid) effects, propagation of plane harmonic waves are studied in the low and high frequencies range. The study involves both dilatational and rotational waves and focuses on the micro-stiffness and micro-inertia effects on the dispersion and attenuation of these waves.


      PubDate: 2016-06-15T10:21:53Z
       
  • Two-dimensional translation, rocking, and waves in a building during
           soil-structure interaction excited by a plane earthquake SV-wave pulse
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Vlado Gičev, Mihailo D. Trifunac, Nebojša Orbović
      A two-dimensional (2-D) model of a building supported by a rectangular, flexible foundation embedded in the soil is analyzed for excitation by an incident plane SV-wave. The incidence is below the critical angle. The building is assumed to be anisotropic and linear while the soil and the foundation are assumed to be isotropic and can experience nonlinear deformations. In general the work spent for the development of nonlinear strains in the soil can consume a significant part of the input wave energy and thus less energy is available for the excitation of the building. We show that the energy distribution in the building depends on the nature of the incident wave and differs substantially between the cases of incident P- and SV-waves. However, for both excitation by a plane SV-wave pulse and excitation by a P-wave, we show that the nonlinear response in the soil and the foundation does not significantly change the nature of excitation of the base of the building. It is noted that the building response can be approximated by translation and rocking of the base only for excitation by long, strong motion waves.


      PubDate: 2016-06-15T10:21:53Z
       
  • Reducing railway-induced ground-borne vibration by using open trenches and
           soft-filled barriers
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): D.J. Thompson, J. Jiang, M.G.R. Toward, M.F.M. Hussein, E. Ntotsios, A. Dijckmans, P. Coulier, G. Lombaert, G. Degrande
      A trench can act as a barrier to ground vibration and is a potential mitigation measure for low frequency vibration induced by surface railways. However, to be effective at very low frequencies the depth required becomes impractical. Nevertheless, for soil with a layered structure in the top few metres, if a trench can be arranged to cut through the upper, soft layer of soil, it can be effective in reducing the most important components of vibration from the trains. This study considers the possibility of using such a realistically feasible solution. Barriers containing a soft fill material are also considered. The study uses coupled finite element / boundary element models expressed in terms of the axial wavenumber. It is found to be important to include the track in the model as this determines how the load is distributed at the soil's surface which significantly affects the insertion loss of the barrier. Calculations are presented for a range of typical layered grounds in which the depth of the upper soil layer is varied. Variations in the width and depth of the trench or barrier are also considered. The results show that, in all ground conditions considered, the notional rectangular open trench performs best. The depth is the most important parameter whereas the width has only a small influence on its performance. More practical arrangements are also considered in which the sides of the trench are angled. Barriers consisting of a soft fill material are shown to be much less effective than an open trench but still have some potential benefit. It is found that the stiffness of the barrier material and not its impedance is the most important material parameter.


      PubDate: 2016-06-15T10:21:53Z
       
  • Two-dimensional numerical modeling of fault rupture propagation through
           earth dams under steady state seepage
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Mahda Mortazavi Zanjani, Abbas Soroush, Mohammad Khoshini
      This paper studies numerically the phenomenon of dip-slip faulting through homogeneous and zoned earth dams under steady state seepage conditions. Normal and reverse faults with various dip angles are included in this study. Two different materials, a clayey soil and a sand-clay mixture, for the homogeneous dam and core of the zoned dam are considered. The results show that the slope of the fault-induced rupture paths is independent of the fault orientation and its location at the base of the dam. The path of fault propagation near the dam surface could be mainly described by the conventional failure theories in the passive and active states. It is also possible to define general patterns for the propagation of rupture inside the body of the earth dams. These patterns are mainly characterized by the location, orientation and mechanism of the fault. The results indicate that reverse faults and mixed materials are responsible for comparatively higher pore water pressures. Emphasizing on engineering significance of the results, the general effects of rupture on the safety of the dams are also discussed.


      PubDate: 2016-06-15T10:21:53Z
       
  • Vibration characterization of fully-closed high speed railway subgrade
           through frequency: Sweeping test
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Liangliang Wang
      This paper presents the vibration characteristics of a new type fully-closed railway subgrade (FCRS) through field frequency – sweeping test. The FCRS, which uses semi-grid modified cement-based compound material as waterproof layer, is designed to solve serious subgrade damage problems induced by expansive soil. Dynamic stress sensors and accelerometers were installed at various locations in FCRS to monitor dynamic response. The results show that the attenuation regularities of dynamic stress and acceleration along subgrade depth were significantly affected by excitation frequency and semi-grid waterproof layer. The pronounced frequency of FCRS investigated in this paper was gently influenced by its layer system, and gradually changed from 20Hz to 22Hz as depth increased.


      PubDate: 2016-06-15T10:21:53Z
       
  • Visco-elastic imperfect bonding effect on dynamic response of a
           non-circular lined tunnel subjected to P and SV waves
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Xue-Qian Fang, He-Xin Jin
      A visco-elastic interface model is proposed to investigate the dynamic stress around a non-circular lined tunnel subjected to P and SV waves, and the analytical solutions of displacements and stresses are obtained. The wave function expansion method combining with the conformal transformation method is applied to express the wave fields around the tunnel. To obtain the analytical solution, the non-circular tunnel is mapped into an annular region. A visco-elastic interface model with elastic and viscosity coefficients is introduced to analyze the interface effect. In numerical examples, the effects of stiffness parameter and viscosity coefficient of interface on the dynamic stress under different wave frequencies are discussed. Comparison with existing numerical results is given to validate this dynamic model.


      PubDate: 2016-06-15T10:21:53Z
       
  • Dynamic stiffness of monopiles supporting offshore wind turbine generators
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Masoud Shadlou, Subhamoy Bhattacharya
      Very large diameter steel tubular piles (up to 10m in diameter, termed as XL or XXL monopiles) and caissons are currently used as foundations to support offshore Wind Turbine Generators (WTG) despite limited guidance in codes of practice. The current codes of practice such as API/DnV suggest methods to analysis long flexible piles which are being used (often without any modification) to analyse large diameter monopiles giving unsatisfactory results. As a result, there is an interest in the analysis of deep foundation for a wide range of length to diameter (L/D) ratio embedded in different types of soil. This paper carries out a theoretical study utilising Hamiltonian principle to analyse deep foundations ( L / D ≥ 2 ) embedded in three types of ground profiles (homogeneous, inhomogeneous and layered continua) that are of interest to offshore wind turbine industry. Impedance functions (static and dynamic) have been proposed for piles exhibiting rigid and flexible behaviour in all the 3 ground profiles. Through the analysis, it is concluded that the conventional Winkler-based approach (such as p–y curves or Bean-on-Dynamic Winkler Foundations) may not be applicable for piles or caissons having aspect ratio less than about 10 to 15. The results also show that, for the same dimensionless frequency, damping ratio of large diameter rigid piles is higher than long flexible piles and is approximately 1.2–1.5 times the material damping. It is also shown that Winkler-based approach developed for flexible piles will under predict stiffness of rigid piles, thereby also under predicting natural frequency of the WTG system. Four wind turbine foundations from four different European wind farms have been considered to gain further useful insights.


      PubDate: 2016-06-15T10:21:53Z
       
  • Site-dependent shear-wave velocity equations versus depth in California
           and Japan
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Su-Yang Wang, Hai-Yun Wang
      Shear-wave velocity of the near-surface ground is an important soil property in earthquake and civil engineering. Using the data from 643 boreholes from the KiK-net in Japan and 135 boreholes from California where the shear-wave velocity profile reaches at least 30m, firstly, we classify sites by building code, then build site-dependent relationships between travel time and depth by regression utilizing the logarithmic model and power-law model, lastly, we get shear-wave velocity equations versus depth based on the mathematical relationship between travel time and velocity. The results show that: (1) the travel time is strongly correlated with depth, and the Pearson correlation coefficients range between 0.867 and 0.978. (2) there is a certain difference between linear velocity equations and power-law velocity equations, and the power-lower equations are generally more close to measured data than linear equations except for class E in Japan and class D in California. (3) the velocities are similar at the sites of each class for different regions but that the gradient of velocity with depth vary between different regions.


      PubDate: 2016-06-15T10:21:53Z
       
  • A linearized approach for the seismic response analysis of flexible cable
           net structures
    • Abstract: Publication date: September 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 88
      Author(s): Yang Xiang, Yongfeng Luo, Xiaonong Guo, Zhe Xiong, Zuyan Shen
      Cable net structures are characterized by significant geometrical nonlinear properties. The linear modal superposition method (LMSM), which ignores the effect of nonlinearity, is believed not suitable for the seismic response analysis of this kind of structures. To conquer the drawback of LMSM, a non-iterative linearization method (NILM) is proposed in this paper. An energy parameter named the “stiffness parameter” is utilized in generating the nonlinear equivalent single degree of freedom (ESDF) systems for the dominant vibration modes of cable nets. The nonlinear stiffness of an ESDF system is simulated by a quadratic function about the equivalent displacement. Based on a stochastic linearization process, the relationship between the equivalent linear stiffness and the displacement response of a modal ESDF system is established. Then the structural responses are computed according to the design response spectra through a non-iterative procedure. Finally, the effectiveness of the proposed NILM is illustrated by a numerical example that carried out on a trapezoid-shaped cable net supported curtain wall structure. It is demonstrated that the proposed NILM, which takes the stiffness hardening effect into consideration, could not only yield better results than the LMSM does, but also exhibit satisfying timesaving property over the nonlinear RHA.


      PubDate: 2016-06-15T10:21:53Z
       
  • Editorial Board / Aims and Scope
    • Abstract: Publication date: August 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 87




      PubDate: 2016-06-15T10:21:53Z
       
  • Evidence of complex site effects and soil non-linearity numerically
           estimated by 2D vs 1D seismic response analyses in the city of Xanthi
    • Abstract: Publication date: August 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 87
      Author(s): Olga Stamati, Nikolaos Klimis, Theologos Lazaridis
      This study discusses the effects of local site conditions on earthquake ground motion for city of Xanthi, North-Eastern Greece, focusing on the influence of complex site effects and soil non-linearity. Although city of Xanthi is characterized as a low seismicity area, documented strong earthquake events of past centuries indicate the necessity of an appropriate estimation of ground surface motion of the region. Therefore, a typical 2D cross-section along the city following an E-W direction is constructed, based on the synthesis of available geological, geotechnical and geophysical data of the broader area. 1D and 2D numerical models are generated utilizing the Finite Difference Method and site response is investigated for different seismic scenarios. Wave amplification is captured as a result of 1D resonance phenomena integrated with potential 2D complex wave effects, due to lateral propagation of the locally generated at the discontinuities surface waves. The additional, relatively to 1D, 2D amplification or de-amplification of ground shaking, in terms of its amplitude and its spectral content is quantified. The impact of soil deposits non-linearity on amplification level, as well as, on generated 2D wave fields is considered by implementing both equivalent-linear and non-linear approaches. The results reveal that, across the city, spatial variation of ground surface motion is obvious, attributed primarily to the variation of subsurface soil profiles. 2D wave effects have been generated signifying that, at particular site locations, ground motion is additionally amplified or de-amplified with respect to 1D response. However, 2D versus 1D differentiation has been calculated of ±20% in terms of PGA and spectral accelerations up to 1.0s, in the majority of the examined sites, implying that site response even though, influenced by 2D resonance phenomena, could be sufficiently captured by an 1D approach. Moreover, it is shown that if soil non-linearity is properly accounted for, it may play an important role on the estimated ground response, since non-linear approach seems to produce lower amplification levels with regard to 1D and 2D equivalent-linear approaches. As a general trend across the investigated site, for the entity of the various scenarios, the numerically calculated response spectra exceed EC8 seismic code provisions.


      PubDate: 2016-06-15T10:21:53Z
       
  • Wavelet-based generation of spatially correlated accelerograms
    • Abstract: Publication date: August 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 87
      Author(s): Kaushik Sarkar, Vinay K. Gupta, Riya C. George
      For the seismic analysis of complex or nonlinear extended structures, it is useful to generate a set of properly correlated earthquake accelerograms that are consistent with a specified seismic hazard. A new simulation approach is presented in this paper for the generation of ensembles of spatially correlated accelerograms such that the simulated motions are consistent with (i) a parent accelerogram in the sense of temporal variations in frequency content, (ii) a design spectrum in the mean sense, and (iii) with a given instantaneous coherency structure. The formulation is based on the extension of stochastic decomposition technique to wavelet domain via the method of spectral factorization. A complex variant of the modified Littlewood-Paley wavelet function is proposed for the wavelet-based representation of earthquake accelerograms, such that this explicitly brings out the phase information of the signal, besides being able to decompose it into component time-histories having energy in non-overlapping frequency bands. The proposed approach is illustrated by generating ensembles of accelerograms at four stations.


      PubDate: 2016-06-15T10:21:53Z
       
  • Engineering analysis of measured rotational ground motions at GVDA
    • Abstract: Publication date: August 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 87
      Author(s): Jianming Yin, Robert L. Nigbor, Qingjun Chen, Jamison Steidl
      Characteristics of rotational earthquake ground motions and their effects on structural response are not yet well-defined. Recording rotational ground motions directly in free field is in its infancy, and simultaneous six-component earthquake measurements are being accumulated slowly. A six-degree-of-freedom (6DOF) ground motion observation system was installed in the Garner Valley Downhole Array (GVDA), a very well-characterized and well-instrumented geotechnical array in Southern California. Since 2008, six-component free-field earthquake ground motions have been recorded from hundreds of earthquakes with a relatively wide range of hypocentral distances and magnitudes. In this paper, analysis was conducted to develop the characteristics of these measured rotational ground motions. Linear relationships between peak rotation velocity and peak ground acceleration were found, similar to previous 6DOF measurements in Taiwan and Japan. Ratios of rotation to translation as a function of hypocentral distance show larger ground rotations at closer distance, and that rotational ground motions tend to attenuate more rapidly than corresponding translational ground motions. Measured rotational motions show differences from estimations using elastic plane wave theory when using simple local apparent wave velocities. Finally, preliminary empirical relationships for rotational response spectra are estimated for earthquake engineering applications.


      PubDate: 2016-06-15T10:21:53Z
       
  • Site classification for strong motion stations in Gujarat, India using
           response spectral ratio
    • Abstract: Publication date: August 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 87
      Author(s): Pallabee Choudhury, Sumer Chopra, Ketan Singha Roy
      We propose a site classification scheme of strong motion sites of Gujarat, India based on predominant period estimated from 5% damped mean H/V response spectral ratio following the site classification scheme of Di Alessandro et al. [1] which is an extended scheme of Zhao et al. [2]. The 23 strong motion sites in Gujarat were classified into seven classes based on predominant period of the sites. A total of 388 strong motion records from 223 earthquakes varying in magnitude between 2.5 and 5.6 are utilized for classification of the sites. Most of the records are from local earthquakes with hypocentral distance less than 50km. Previous attempts to classify sites based on local site conditions and geology could not incarcerate the site characteristics and variability within the same geological conditions. The presented site characterization methodology is quick and inexpensive where for instance; sites with thick sedimentary column like basins can be identified quickly without invasive analysis. Also, this classification based on predominant period, which contains both velocity and thickness of resonant layers in its definition, is better than site classification based on Vs30 criteria which captures the site response for only 30m. The site effects captured in this classification scheme can be utilized in the ground motion prediction equations developed for the region.


      PubDate: 2016-06-15T10:21:53Z
       
  • Multi-objective optimization of a dissipative connection for seismic
           protection of wall-frame structures
    • Abstract: Publication date: August 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 87
      Author(s): Rita Greco, Giuseppe Carlo Marano
      This paper deals with the optimum design of a passive seismic control strategy which adopts a linear dissipative connection in a wall-frame system. The two sub-structures, the wall and the frame, respectively, are modeled as single degree of freedom systems, and are excited by a ground motion represented by a filtered non stationary stochastic process. The passive control strategy is based on a "global protection", which aims to protect both sub-structures. For this purpose, a multi-objective optimum design is formulated where two conflicting objective functions coexist: these are the displacement of the frame and the shear in the wall. In order to obtain the optimum solution in terms of Pareto set, a genetic algorithm approach—the NSGA-II—is adopted. The novelty of the proposed method is the use of a multi-dimensional criterion for the design of the dissipative connection and to consider a global seismic protection criterion. This is a very important issue in modern Technical Codes, where several performance requirements are fixed and often conflicting.


      PubDate: 2016-06-15T10:21:53Z
       
  • Soil reaction to lateral harmonic pile motion
    • Abstract: Publication date: August 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 87
      Author(s): George Anoyatis, George Mylonakis, Anne Lemnitzer
      The analytical representation of dynamic soil reaction to a laterally-loaded pile using 3D continuum modeling is revisited. The governing elastodynamic Navier equations are simplified by setting the dynamic vertical normal stresses in the soil equal to zero, which uncouples the equilibrium in vertical and horizontal directions and allows a closed-form solution to be obtained. This physically motivated approximation, correctly conforming to the existence of a free surface, was not exploited in earlier studies by Tajimi, Nogami and Novak and leads to a weaker dependence of soil response to Poisson's ratio which is in agreement with numerical solutions found in literature. The stress and displacement fields in the soil and the associated reaction to an arbitrary harmonic pile displacement are derived analytically using pertinent displacement potentials and eigenvalue expansions over the vertical coordinate. Both infinitely long piles and piles of finite length are considered. Results are presented in terms of dimensionless parameters and graphs that highlight salient aspects of the problem. A detailed discussion on wave propagation and cutoff frequencies based on the analytical findings is provided. A new dimensionless frequency parameter is introduced to demonstrate that the popular plane-strain model yields realistic values for soil reaction only at high frequencies and low Poisson's ratios.


      PubDate: 2016-06-15T10:21:53Z
       
  • Corrigendum to: “Generalized cyclic p–y curve modeling for
           analysis of laterally loaded piles” [Soil Dyn. Earthq. Eng. 63
           (2014) 138–149]
    • Abstract: Publication date: August 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 87
      Author(s): Mehdi Heidari, Hesham El Naggar, Mojtaba Jahanandish, Arsalan Ghahraman



      PubDate: 2016-06-15T10:21:53Z
       
  • Corrigendum to "Limit sliding-block seismic displacement for landslide
           triggering along slip surfaces consisting of saturated sand". Soil
           Dynamics and Earthquake Engineering 79 (2015) 265–277
    • Abstract: Publication date: August 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 87
      Author(s): Constantine A. Stamatopoulos



      PubDate: 2016-06-15T10:21:53Z
       
  • Editorial Board / Aims and Scope
    • Abstract: Publication date: July 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 86




      PubDate: 2016-06-15T10:21:53Z
       
  • Three-dimensional P- and S-wave velocity profiling of geotechnical sites
           using full-waveform inversion driven by field data
    • Abstract: Publication date: August 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 87
      Author(s): Arash Fathi, Babak Poursartip, Kenneth H. Stokoe II, Loukas F. Kallivokas
      We discuss the application of a recently developed full-waveform-inversion-based technique to the imaging of geotechnical sites using field-collected data. Specifically, we address the profiling of arbitrarily heterogeneous sites in terms of P- and S-wave velocities in three dimensions, using elastic waves as probing agents. We cast the problem of finding the spacial distribution of the elastic soil properties as an inverse medium problem, directly in the time domain, and use perfectly-matched-layers (PMLs) to account for the semi-infinite extent of the site under investigation. After briefly reviewing the theoretical and computational aspects of the employed technique, we focus on the characterization of the George E. Brown Jr. Network for Earthquake Engineering Simulation site in Garner Valley, California (NEES@UCSB). We compare the profiles obtained from our full-waveform-inversion-based methodology against the profiling obtained from the Spectral-Analysis-of-Surface-Waves (SASW) method, and report agreement. In an attempt to validate our methodology, we also compare the recorded field data at select control sensors that were not used for the full-waveform inversion, against the response at the same sensors, computed based on the full-waveform-inverted profiles. We report very good agreement at the control sensors, which is a strong indicator of the correctness of the inverted profiles. Overall, the systematic framework discussed herein seems robust, general, practical, and promising for three-dimensional site characterization purposes.


      PubDate: 2016-05-11T05:57:37Z
       
  • The application of CFRP to strengthen buried steel pipelines against
           subsurface explosion
    • Abstract: Publication date: August 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 87
      Author(s): M. Mokhtari, A. Alavi Nia
      Multiple explosions in the route of oil and gas transmission pipelines during recent years demonstrate that terrorist attacks and sabotages have unfortunately increased. The present investigation is carried out numerically in order to minimize the amount of damages imposed on steel pipelines under close-in explosions. This research presents a novel concept, using CFRP (Carbon Fiber Reinforced Polymer) to strengthen the wall of steel pipelines against these incidents. For this purpose, a full coupled 3D finite element model developed using a combined Eulerian-Lagrangian method. The simplified Johnson-Cook material model, the JWL equation of state, and the ideal gas equation of state were employed for modeling the pipe material behavior, charge detonation, and air, respectively. Mechanical behavior of the composite wrap was simulated using an anisotropic material model and the damage initiation criteria were based on Hashin's theory. In addition, soil mass behavior was modeled applying a Drucker-Prager strength criterion with piecewise hardening and hydro tensile limit accompanied by Mie-Grüneisen equation of state. Several comparisons carried out between the results from present investigation and those from field and empirical studies and good agreements were observed. The results show that using a proper thickness of CFRP wrap for every particular circumstance can significantly improve the performance of steel pipelines under blast loads. For instance, in the current example, maximum equivalent strains developed in the most of the studied pipelines decreased by over 30% (up to 64%) with the application of 4-mm-thickness CFRP wrap. The present study contributes to protective design of steel pipelines.


      PubDate: 2016-05-11T05:57:37Z
       
  • Simulation and generation of spectrum-compatible ground motions based on
           wavelet packet method
    • Abstract: Publication date: August 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 87
      Author(s): Yanan Li, Guoxin Wang
      This paper deals with the problem of generating spectrum-compatible artificial accelerograms for seismic dynamic analysis of engineering projects. A wavelet-packet-based, two-step procedure for the issue is proposed. The first step is to generate acceleration time history that could account for temporal and frequency non-stationarities of recorded ground motions. The second step is to decompose it into a desired number of wavelet packet vectors with high frequency resolution and non-overlapping frequency contents. Then each wavelet packet vector is scaled suitably and iteratively for the response spectrum of the simulated accelerogram to fit a specified design spectrum. The advantages of this procedure are that it can simulate user-specified acceleration time history with only 6 input parameters and the adjusted accelerogram has similar characteristics to the recorded one. The proposed procedure has been illustrated by simulating and modifying acceleration time history that are compatible with two different design spectrums for nuclear power plants. In addition, iterative efficiency of the method is investigated by simulating and adjusting acceleration time history for 100 successive times. The maximum relative error of the 76 period control points can reach 6% or below. Results show that the proposed method is effective and practical to generate and find spectrum-compatible ground motions with both stochastic and deterministic aspects.


      PubDate: 2016-05-11T05:57:37Z
       
  • Seismic response of deep Quaternary sediments in historical center of
           L’Aquila City (central Italy)
    • Abstract: Publication date: August 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 87
      Author(s): Ermanno Ragozzino
      On 6 April 2009 a M w =6.1 earthquake produced severe destruction and damage over the historic center of L’Aquila City (central Italy), in which the accelerometer stations AQK and AQU recorded a large amount of near-fault ground motion data. This paper analyzes the recorded ground motions and compares the observed peak accelerations and the horizontal to vertical response spectral ratios with those revealed from numerical simulations. The finite element method is considered herein to perform dynamic modeling on the soil profile underlying the seismic station AQU. The subsurface model, which is based on the reviewed surveys that were carried out in previous studies, consists of 200–400m of Quaternary sediments overlying a Meso-Cenozoic carbonate bedrock. The Martin-Finn-Seed's pore-water pressure model is used in the simulations. The horizontal to vertical response spectral ratio that is observed during the weak seismic events shows three predominant frequencies at about 14Hz, 3Hz and 0.6Hz, which may be related to the computed seismic motion amplification occurring at the shallow colluvium, at the top and base of the fluvial-lacustrine sequence, respectively. During the 2009 L’Aquila main shock the predominant frequency of 14Hz shifts to lower values probably due to a peculiar wave-field incidence angle. The predominant frequency of 3Hz shifts to lower values when the earthquake magnitude increases, which may be associated to the progressive softening of soil due to the excess pore-water pressure generation that reaches a maximum value of about 350kPa in the top of fluvial-lacustrine sequence. The computed vertical peak acceleration underestimates the experimental value and the horizontal to vertical peak acceleration ratio that is observed at station AQU decreases when the earthquake magnitude increases, which reveals amplification of the vertical component of ground motion probably due to near-source effects.


      PubDate: 2016-05-11T05:57:37Z
       
  • Dynamic response of a pile embedded into a layered soil
    • Abstract: Publication date: August 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 87
      Author(s): Mario Martinelli, Alberto Burghignoli, Luigi Callisto
      This paper studies the seismic response of a foundation pile embedded in a saturated coarse-grained deposit. The pile response is examined through a series of three-dimensional dynamic finite element analyses incorporating an advanced plasticity soil model and implementing a fully coupled interaction between the soil skeleton and the pore fluid. The study is mainly focused on the development of the internal forces in a pile immersed into a deposit including two soil layers with a different stiffness, and accounts for the development of excess pore water pressures during the seismic motion. The effects of the initial porosity and of the permeability of the soil layers are investigated, together with the effects of changing the pile length, the pile diameter, and the boundary condition at the top of the pile. Finally, the results of the finite element simulations are used as a benchmark to evaluate the capability of a number of simplified predictive methods and to provide guidance for their implementation.


      PubDate: 2016-05-11T05:57:37Z
       
  • Improved Modal Pushover Analysis in seismic assessment of asymmetric plan
           buildings under the influence of one and two horizontal components of
           ground motions
    • Abstract: Publication date: August 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 87
      Author(s): André Belejo, Rita Bento
      The Improved Modal Pushover Analysis (IMPA) is a multimode procedure that has the advantage of redefining the lateral load applied, when comparing with the multimode current methods; hence, instead of considering the elastic deformed shape, it is possible to consider the deformed shape of the structure when it is behaving inelastically, as a pattern. The IMPA was proposed in the past and was successfully applied in the seismic assessment of bridges, the main objective of this work being to explore IMPA in buildings. For this purpose the seismic demands of two asymmetric plan buildings are herein estimated by means of IMPA and compared to Nonlinear Dynamic Analyses (NDA) and to current reference Nonlinear Static Procedures (NSPs): Modal Pushover Analysis (MPA) and two other NSPs that are proposed in American and European seismic codes (ASCE/SEI 41-06 NSP and N2 method respectively). In the latter, an extended version (extended N2) is considered, taking into account both the torsional and the higher mode effects. The seismic response of the two buildings herein studied is obtained through two different approaches: the first regarding only one component of ground motion, while the second considers both components of ground motion acting simultaneously. The seismic assessment of both buildings is performed in terms of pushover curves, top displacement ratios, lateral displacements profiles, interstorey drifts, normalized top displacements and shear forces.


      PubDate: 2016-05-11T05:57:37Z
       
  • Surface-wave testing of soil sites using multichannel simulation with
           one-receiver
    • Abstract: Publication date: August 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 87
      Author(s): Shibin Lin, Jeramy C. Ashlock
      This paper presents a study on the application of the multichannel simulation with one-receiver (MSOR) surface-wave testing method for geophysical profiling of soil sites. The MSOR method reverses the roles of source and receiver in the widely-used multi-channel analysis of surface waves (MASW) method. To examine the feasibility and accuracy of utilizing MSOR for soil sites, finite element simulations of MSOR testing are performed for three types of soil profiles containing horizontal interfaces, a vertical fault, and a dipping interface, respectively. The effects of variations in the moving impact locations on the uncertainty and repeatability of the dispersion trends are analyzed for the different soil profiles. Real-world case studies are carried out to examine the equivalency of the MSOR and MASW methods for quantifying surface-wave dispersion trends of soil profiles, as well as the advantages of MSOR testing with embedded geophones to obtain more extensive multimodal dispersion data. From the computational simulations and field case studies, MSOR is demonstrated to be equivalent to MASW testing for practical purposes. In addition, MSOR has the advantages of reduced instrumentation cost, improved portability, enhanced ability to measure multi-mode dispersion curves by utilizing borehole geophones, and the potential for improving efficiency of 3-D stiffness profiling.


      PubDate: 2016-05-11T05:57:37Z
       
  • Scatter of dynamic response and damage of an arch dam subjected to
           artificial earthquake accelerograms
    • Abstract: Publication date: August 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 87
      Author(s): Jin-Ting Wang, Ai-Yun Jin, Xiu-Li Du, Ming-Xin Wu
      In current engineering practice, artificial earthquake accelerograms are widely used in the seismic design of new dams. This study aims to investigate the seismic response and damage sensitivity of arch dams to artificial ground motions. A total of 32 accelerograms are artificially synthesized based on the design acceleration response spectrum. The nonlinear dynamic response of the Dagangshan Dam, an arch dam in Southwest China, to these artificial accelerograms is investigated. Dynamic response, including displacement and joint opening, and damage distribution are statistically analyzed. Results show that the seismic response and damage to a dam may significantly scatter for various accelerograms, even if the artificial accelerograms have the same response spectra, peak ground accelerations, velocities, and displacements.
      Graphical abstract image

      PubDate: 2016-05-11T05:57:37Z
       
  • Shake-table tests and numerical simulation of an innovative isolation
           system for highway bridges
    • Abstract: Publication date: July 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 86
      Author(s): Jianzhong Li, Nailiang Xiang, Hu Tang, Zhongguo Guan
      Damage investigation of small to medium-span highway bridges in Wenchuan earthquake revealed that typical damage of these bridges included: sliding between laminated-rubber bearings and bridge girders, concrete shear keys failure, excessive girder displacements and even span collapse. However, the bearing sliding could actually act as a seismic isolation for piers, and hence, damage to piers for these bridges was minor during the earthquake. Based on this concept, an innovative solation system for highway bridges with laminated-rubber bearings is developed. The system is comprised of typical laminated-rubber bearings and steel dampers. Bearing sliding is allowed during an earthquake to limit the seismic forces transmitting to piers, and steel dampers are applied to restrict the bearing displacements through hysteretic energy dissipation. As a major part of this research, a quarter-scale, two-span bridge model was constructed and tested on the shake tables to evaluate the performance of this isolation system. The bridge model was subjected to a Northridge and an artificial ground motion in transverse direction. Moreover, numerical analyses were conducted to investigate the seismic performance of the bridge model. Besides the test bridge model, a benchmark model with the superstructure fixed to the substructure in transverse direction was also included in the numerical analyses. Both the experimental and the numerical results showed high effectiveness of this proposed isolation system in the bridge model. The system was found to effectively control the pier-girder relative displacements, and simultaneously, protect the piers from severe damage. Numerical analyses also validated that the existing finite element methods are adequate to estimate the seismic response of bridges with this isolation system.


      PubDate: 2016-05-11T05:57:37Z
       
  • Preliminary empirical scaling of pseudo relative velocity spectra in
           Serbia from the Vrancea earthquakes
    • Abstract: Publication date: July 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 86
      Author(s): V.W. Lee, M.D. Trifunac, B.Đ. Bulajić, M.I. Manić
      First frequency-dependent empirical scaling equations of pseudo-relative velocity spectral amplitudes (PSV) of strong earthquake ground motions in the former Yugoslavia were introduced in the mid-1990s by Lee and Trifunac (1990) [15]. This followed the development of the Fourier spectral amplitudes (FS) scaling equations by Lee and Trifunac (1993) [17] in terms of earthquake source parameters, and the region-specific frequency dependent attenuation function given by Lee and Trifunac (1992) [16]. More recently, a new frequency-dependent attenuation function was developed for central and eastern Serbia for earthquakes of intermediate and large magnitudes and for large epicentral distances—exceeding 300km—suggested by Lee et al. (2016) [19] that occur in the Vrancea source region in Romania. In this paper we use this frequency-dependent attenuation function to develop empirical scaling equations for PSV spectral amplitudes in Serbia. These scaling equations will form a basis for macro- and micro-zoning earthquake hazard studies in Serbia.


      PubDate: 2016-04-29T13:14:02Z
       
  • Small-strain shear modulus of volcanic granular soil: An experimental
           investigation
    • Abstract: Publication date: July 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 86
      Author(s): Xin Liu, Jun Yang, Gonghui Wang, Longzhu Chen
      While volcanic soils exist in many places around the world, their mechanical behavior is however less extensively studied as compared to the conventional soil type such as quartz sand and clay. This paper presents an experimental study investigating the small-strain shear modulus (G 0) and associated shear wave velocity (V s) of a volcanic granular soil collected from the northeast of Japan that was affected by the devastating 2011 Tohoku earthquake. Reconstituted soil specimens were tested at different packing densities and confining stress levels by using the resonant column technique, and the pressure and density dependence of shear modulus was established for the soil. The study showed that under otherwise similar conditions, the G 0 value of the volcanic soil was markedly lower than that of clean quartz sands, but it tended to increase significantly when the fine particles in the soil were removed. This finding suggests that the presence of fines plays an important role in the mechanical behavior of volcanic soils. A practical model accounting for the influence of fines and the pressure and density dependence is proposed and it is shown to provide reasonable estimates of G 0 for both volcanic soils and clean quartz sands studied.


      PubDate: 2016-04-29T13:14:02Z
       
  • An analytical model for vibration prediction of a tunnel embedded in a
           saturated full-space to a harmonic point load
    • Abstract: Publication date: July 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 86
      Author(s): Zonghao Yuan, Yuanqiang Cai, Zhigang Cao
      The dynamic response of a tunnel embedded in a saturated poroelastic full-space under a vertical harmonic load was investigated by a semi-analytical method. The tunnel was modeled as a thin cylindrical shell surrounded by soil of infinite radial extent. The soil was modeled as a saturated poroelastic full-space. Biot's theory was applied to characterize the soil medium, taking the solid skeleton-pore fluid coupling effects into account. Combined with the boundary conditions at tunnel–soil interface, the coupled equations of the system were solved in the frequency domain with the aid of Fourier decomposition and Fourier transform in the circumferential and longitudinal direction, respectively. Dynamic responses of the tunnel and soil generated by a unit harmonic load applied at the tunnel invert are presented. It is found that the soil permeability and the load frequency have significant influence on the displacements, the stresses and the pore pressure in the saturated soil. In the free field, an increase of the soil permeability leads to a decrease of the soil displacement and pore pressure response. An equivalent single-phase material was used to model the saturated soil and it is found only applicable for soil with lower permeability.


      PubDate: 2016-04-29T13:14:02Z
       
  • Experimental and finite element study of the reverse faulting effects on
           buried continuous steel gas pipelines
    • Abstract: Publication date: July 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 86
      Author(s): Himan Hojat Jalali, Fayaz Rahimzadeh Rofooei, Nader Khajeh Ahmad Attari, Masoud Samadian
      Permanent ground displacement (PGD) caused by surface faulting is considered as one of the most significant hazards affecting buried pipelines. Pipelines crossing reverse-slip faults are subjected to compressive actions (stresses and strains) which can result in buckling of the pipe. In current work, the results obtained from the full-scale laboratory testing and finite element analyses of 4″ (114.3mm) and 6″ (168.3mm) steel gas pipes (without internal pressure) buried inside a split box and subjected to a reverse faulting of 0.6m (pure dip-slip) are presented. These pipes are commonly used in gas distribution lines and networks. The experimental setup, procedure and instrumentation as well as the finite element (FE) modeling of the problem are described in detail. It is observed that the soil failure in the moving part of the split-box occurs along vertical surfaces extending from the sides of the pipe to the ground surface. The experimental results indicate that both pipes exhibit an S-shape deformation with two local buckling sections where the excessive yielding and plastic deformations of the pipes could lead to rupture failure. Both pipes exhibited “diamond-shape” buckled sections. The buckled sections of the pipes in the fixed and moving parts of the split box were unsymmetrical with respect to the fault plane. Using the factor of ovality to measure the pipe cross-section distortion, it is found that the cross-section distortion is more severe for the buckled section of the pipe in the moving part of the split box in comparison to its fixed part. Also, the distance between the buckled sections increases by increasing the pipe diameter, while the distortion of the pipe cross-section increases by increasing the pipe diameter over thickness ratio. Using the FE models that were validated utilizing the experimental results, the maximum equivalent soil–pipe interaction forces and their distribution along the pipes were determined and the results were compared with that of American Lifeline Alliance Guidelines for the Design of Buried Steel Pipe (ALA, 2005) [33]. The obtained maximum bearing force is less than the suggested values by ALA, while the maximum uplift force slightly exceeds those of ALA. The results indicate that for the considered cases, the uplift force is sensitive to the pipe diameter and its relative stiffness, while the ALA (2005, [33]) suggests a constant force for the burial depths considered in this study.


      PubDate: 2016-04-29T13:14:02Z
       
 
 
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