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Journal Cover Soil Dynamics and Earthquake Engineering
  [SJR: 1.482]   [H-I: 45]   [10 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0267-7261
   Published by Elsevier Homepage  [2970 journals]
  • 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
       
  • The 2012 Emilia earthquake (Italy): Geotechnical characterization and
           ground response analyses of the paleo-Reno river levees
    • Abstract: Publication date: July 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 86
      Author(s): Johann Facciorusso, Claudia Madiai, Giovanni Vannucchi
      In 2012 Northern Italy was hit by a seismic sequence with earthquakes of moderate local magnitudes and shallow hypocentral depths. After the main shocks of May 20, collapse of buildings and lifeline ruptures were widely observed in the epicentral area within a distance of about 15km, where large acceleration values with prevailing vertical component were recorded. Locally, at a greater distance, intense and spectacular liquefaction effects were observed. They mainly affected the earthen embankments of the old Reno river channel (paleochannel), and, to a lesser extent, their immediate surroundings. In these far-field areas, ground surface accelerations were significantly low and not consistent with the spreading and extent of the observed liquefaction effects. A detailed geotechnical survey was performed to identify depth, location and behaviour of liquefied soil layers and to analyse their influence on ground response and surface liquefaction effects. Results from in situ and laboratory tests, performed under static and dynamic loading conditions, are presented herein and a complete geotechnical model of the ancient levees and the underlying soil deposit is proposed for numerical site-specific seismic analyses. More attention was paid to analysing the influence of non-linear behaviour of interbedded liquefied sands on the expected surface ground motion. Implications and limits of the results obtained are discussed with, finally, proposals for adjustments to 1-D linear equivalent models operating in the frequency domain, for taking into account stiffness degradation of liquefiable layers at high strain levels.


      PubDate: 2016-05-11T05:57:37Z
       
  • Development of dynamic centrifuge models of underground structures near
           tall buildings
    • Abstract: Publication date: July 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 86
      Author(s): S. Dashti, Y.M.A. Hashash, K. Gillis, M. Musgrove, M. Walker
      A series of six centrifuge experiments was designed and conducted to assess the seismic influence of a mid to highrise building on adjacent shallow underground structures. The buildings modeled in this study (12 and 42 stories) were the tallest structures tested in centrifuge to date. In designing these experiments, it was important to represent the modal frequencies, base shear, base moment, and yield characteristics of realistic mid and highrise structures, in order to transmit realistic seismic demands onto the underground structures. For the midrise structure, it was possible to simulate the height, mass, and three primary modes of response with a simplified, scaled model in centrifuge. For the highrise structure, additional simplifications were necessary due to a limited overhead space. A scaled, single-degree-of-freedom structure could capture the fundamental frequency, mass, and therefore base shear of a representative 42-story highrise building, while other properties were sacrificed. The six experiments with varied payloads required similar base motions to experimentally evaluate the seismic impact of buildings on underground structures. The heavy structures applied an unprecedented demand on the shaking table under increased gravity, which was expected to adversely affect the repeatability of motions. Even though the achieved base motions were significantly de-amplified compared to those desired, their coefficient of variation among six experiments was less than 0.2 in the frequency range of interest (0.2–5Hz), indicating acceptable repeatability. The buildings were instrumented during the centrifuge tests to measure their base shear and roof drifts. The results were consistent with pushover analyses and design requirements, indicating realistic overall stiffness, yielding characteristics, and shear forces transmitted to the foundation. The overall response of the system indicates that, with reasonable approximations, the seismic forces transferred from tall buildings to the foundation soil and an adjacent underground structure can be successfully modeled and evaluated in centrifuge.


      PubDate: 2016-05-11T05:57:37Z
       
  • Editorial Board / Aims and Scope
    • Abstract: Publication date: June 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 85




      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
       
  • On the seismic stability and critical slip surface of reinforced slopes
    • Abstract: Publication date: June 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 85
      Author(s): M. Khosravizadeh, M. Dehestani, F. Kalantary
      Seismic stability of reinforced slopes is investigated using Horizontal Slice Method within the framework of the pseudo-static force. These introduced by constant horizontal or vertical inertial forces and the equilibrium equations for all forces applied to each horizontal slice are considered. A new procedure is introduced which could determine the location and shape of failure surface. The slip surface is a multiplanar surface consisting of a number of inclined linear segments interconnected with various lengths and angles in a plane. The amount of reinforcement forces is used as the objective function in the optimization procedure to determine the shape and location of the critical slip surface. This approach is relatively simple and yields results which are in good agreement with previous findings. Final results revealed that with increase in horizontal seismic acceleration, the reinforcements force increases. With increase in slope angle, the failure surface changes from curve to planar shape.


      PubDate: 2016-04-19T17:26:06Z
       
  • A refined analytical model for earthquake-induced sloshing in
           half–full deformable horizontal cylindrical liquid containers
    • Abstract: Publication date: June 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 85
      Author(s): Spyros A. Karamanos, Angeliki Kouka
      The coupled response of elastic deformable liquid containers of horizontal-cylindrical shape under external seismic excitation is examined, through an analytical methodology, assuming inviscid-incompressible fluid and irrotational-flow conditions. In particular, the case of a half–full horizontal-cylindrical deformable container is examined, considering an analytical series-type solution for the velocity potential function that describes the liquid motion under external excitation. This mathematical analysis extends the solution methodology presented in previous publications of the senior author, taking into account full coupling between sloshing and wall deformation in a rigorous manner, where wall deformation is considered through a sinusoidal assumed-shape function. In the mathematical formulation, the velocity potential is decomposed into three parts: (a) a first part, which represents liquid motion that follows the external excitation, (b) a “convective part”, representing liquid motion associated with free surface elevation (sloshing), and (c) a third part caused by the wall deformation. Using an elegant mathematical manipulation, the coupled transient overall response of the liquid-container system is obtained in an efficient manner. Numerical results are presented in terms of the principal natural frequencies of the coupled system, as well as the system response under strong seismic input, and emphasize on the effects of container aspect ratio on the dynamic behavior of the system. The mathematical formulation for the case of long cylinders results in a simplified model, identical to the simplified “physical model” presented in a previous publication.


      PubDate: 2016-04-19T17:26:06Z
       
  • A spatial correlation model of peak ground acceleration and response
           spectra based on data of the Istanbul Earthquake Rapid Response and Early
           Warning System
    • Abstract: Publication date: June 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 85
      Author(s): Thomas Wagener, Katsuichiro Goda, Mustafa Erdik, James Daniell, Friedemann Wenzel
      Ground motion intensity measures such as the peak ground acceleration (PGA) and the pseudo-spectral acceleration (PSA) at two sites due to the same seismic event are correlated. The spatial correlation needs to be considered when modeling ground-motion fields for seismic loss assessments, since it can have a significant influence on the statistical moments and probability distribution of aggregated seismic loss of a building portfolio. Empirical models of spatial correlation of ground motion intensity measures exist only for a few seismic regions in the world such as Japan, Taiwan and California, since for this purpose a dense observation network of earthquake ground motion is required. The Istanbul Earthquake Rapid Response and Early Warning System (IERREWS) provides one such dense array with station spacing of typically 2km in the urban area of Istanbul. Based on the records of eight small to moderate (M w3.5–M w5.1) events, which occurred since 2003 in the Marmara region, we establish a model of intra-event spatial correlation for PGA and PSA up to the natural period of 1.0s. The results indicate that the correlation coefficients of PGA and short-period PSA decay rapidly with increasing interstation distance, resulting in correlation lengths of approximately 3–4km, while correlation lengths at longer natural periods (above 0.5s) exceed 6km. Finally, we implement the correlation model in a Monte Carlo simulation to evaluate economic loss in Istanbul's district Zeytinburnu due to a M w7.2 scenario earthquake.


      PubDate: 2016-04-19T17:26:06Z
       
  • PGA-PGV/Vs considered as a stress–strain proxy for predicting
           nonlinear soil response
    • Abstract: Publication date: June 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 85
      Author(s): Johanes Chandra, Philippe Guéguen, Luis Fabian Bonilla
      In this paper, a relationship proxy for predicting the nonlinear soil responses is proposed by mean of monitoring the variation of shear wave velocity along vertical array. The recent seismic interferometry by deconvolution method is applied to extract the shear-wave velocity profile throughout the soil column. Using synthetic modeling, this method is shown to be a relevant and an efficient solution for assessing the Vs profile along a vertical seismic array. The ratio between particle velocity and the equivalent linear shear-wave velocity, v*/Vs*, is computed between two successive sensors, and is assumed to be a proxy for strain. The particle acceleration, a*, versus v*/Vs* is proposed as a stress–strain representation for nonlinear analysis of soil response. Using centrifuge tests, v*/Vs* is shown to be a good representation for soil strain, and analysis of the variation of v*/Vs* as a function of a* allows the nonlinear soil response to be determined in an earthquake situation. These relationship proxies are finally applied to the Japanese K-NET and KiK-net in-situ data, where Vs 30 is used instead of Vs* for practical purposes related to site classification recommendations.


      PubDate: 2016-04-19T17:26:06Z
       
  • A numerical and experimental study of hollow steel pile in layered soil
           subjected to vertical dynamic loading
    • Abstract: Publication date: June 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 85
      Author(s): D. Bhowmik, D.K. Baidya, S.P. Dasgupta
      This paper presents an investigation of the nonlinear behaviour of single piles subjected to varying levels of vertical dynamic load. A good number of tests are performed for the understanding of the dynamic behaviour of single hollow steel piles embedded in layered soil. Experimental results are validated with results obtained from a nonlinear numerical analysis using commercially available Finite Element Method (FEM) based software. The results of numerical analysis and experimental investigations showed that the length of pile has significant influence on resonant frequency and amplitude of the pile foundation. It has also been found that the slippage of pile from the surrounding soil considerably affects the resonance frequency and amplitude of the soil–pile foundation system.


      PubDate: 2016-04-19T17:26:06Z
       
  • Multi-step prediction of strong earthquake ground motions and seismic
           responses of SDOF systems based on EMD-ELM method
    • Abstract: Publication date: June 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 85
      Author(s): Dixiong Yang, Kaisheng Yang
      This paper proposes a new multi-step prediction method of EMD-ELM (empirical mode decomposition-extreme learning machine) to achieve the short-term prediction of strong earthquake ground motions. Firstly, the acceleration time histories of near-fault ground motions with nonstationary property are decomposed into several components of intrinsic mode functions (IMFs) with different characteristic scales by the technique of EMD. Subsequently, the ELM method is utilized to predict the IMF components. Moreover, the predicted values of each IMF component are superimposed, and the short-term prediction of ground motions is attained with low error. The predicted results of near-fault acceleration records demonstrate that the EMD-ELM method can realize multi-step prediction of acceleration records with relatively high accuracy. Finally, the elastic and inelastic acceleration, velocity and displacement responses of single degree of freedom (SDOF) systems are also predicted with satisfactory accuracy by EMD-ELM method.


      PubDate: 2016-04-08T22:23:32Z
       
  • Non-linear modeling of seismic isolation systems made of recycled
           tire-rubber
    • Abstract: Publication date: June 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 85
      Author(s): Santiago Brunet, Juan Carlos de la Llera, Eduardo Kausel
      This article considers the effectiveness of a seismic isolation system composed of a shallow layer of soil mixed with sand and rubber from shredded tires. A thorough review of past work is first provided, which is then followed by an evaluation of the constitutive properties of sand-rubber soil mixtures when these undergo large states of deformation and slip. Finally, a comprehensive set of simulations that involve a structure underlain by a strongly non-linear, seismic isolating layer when subjected to a variety of actual earthquakes scaled to various peak accelerations, are considered in detail. It is shown that the concept of using soil-rubber mixtures for the purposes of seismic isolation appears promising. A thickness for the rubber–soil mixture of just 2–3m is likely to be enough to achieve good levels of reductions in the seismic response of the structure. This suggests the desirability of following these analyses with large-scale experimental verifications, not only to fully validate the concept, but also to quantify and assess the numerical predictions with our simple even if non-linear mechanical models, and verify the large-strain constitutive properties of the soil mixtures inferred from laboratory analyses.


      PubDate: 2016-04-08T22:23:32Z
       
  • Geospatial modelling of shear-wave velocity and fundamental site period of
           Quaternary marine and glacial sediments in the Ottawa and St. Lawrence
           Valleys, Canada
    • Abstract: Publication date: June 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 85
      Author(s): Miroslav Nastev, Michel Parent, Martin Ross, Danielle Howlett, Nicolas Benoit
      The shear wave velocity of surficial sediments (V S) and the fundamental site period (T O) are important parameters for analysis of the free-field seismic response. Their spatial distribution in the Ottawa and St. Lawrence Valleys, Canada, was determined applying a standardized method consisting of (i) updating the Quaternary geology; (ii) classifying the surficial units with similar physical properties into three broad categories: upper sandy sediments, intermediate clayey sediments and basal glacial and non-glacial deposits; (iii) delineating the spatial thickness of each category by way of 3D geologic modelling; (iv) sorting of available geophysical data with respect to each individual category and assigning representative VS relationships: a power velocity-depth function for sand and clay units combined, V S=119+8.1 Depth0.5 (m/s), and a constant interval V S equal to the observed geometric mean velocity for glacial and non-glacial deposits, V S=385 (m/s). The respective T O values were computed as the ratio between the soil thickness and the average V S from ground surface to the bedrock. Validation of model results was conducted with V S and T O field data and available T O estimates from detailed urban-scale seismic zonation studies. The analyses of the uncertainty originating from the variation of the V S measurements showed that the standard deviations were roughly one-third of the modelled V S and T O values.


      PubDate: 2016-04-08T22:23:32Z
       
  • Mutual seismic assessment and isolation of different art objects
    • Abstract: Publication date: June 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 85
      Author(s): Stefano Sorace, Gloria Terenzi, Camilla Bitossi, Elena Mori
      New developments of a research programme dedicated to the seismic performance assessment and base isolation protection of art objects are presented in this paper. The investigation field has been extended from massive marble statues, considered at first step of this study, to slender free-standing columns, and bronze statues with highly vulnerable geometrical portions. A semicircular marble column and an equestrian bronze sculpture located in the main hall of the Restoration Laboratories of the Opificio delle Pietre Dure Institute in Florence are examined as representative case studies of the two classes, respectively. Rocking and sliding effects are simulated in the time-history assessment analyses of both artefacts, carried out by introducing all simultaneous components of seismic action as input. The results show an overturning-related near-collapse response of the column, and a plasticization-induced collapse of the statue, at the maximum considered earthquake level. In view of the different material and structural characteristics of the two artworks and several other art objects and equipments situated in the same hall, a mutual advanced seismic protection strategy is adopted, consisting in the base isolation of the floor by means of double curved surface sliders. This retrofit measure guarantees completely undamaged response conditions of the column and the statue, without requiring direct interventions on the two artworks. At the same time, the base-isolated floor constitutes a highly protective support for the hi-tech equipments housed in the Laboratories, as well as for any other artefact to be placed on it in the future.


      PubDate: 2016-04-08T22:23:32Z
       
  • Using elastic bridge bearings to reduce train-induced ground vibrations:
           An experimental and numerical study
    • Abstract: Publication date: June 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 85
      Author(s): Xiaozhen Li, Zhijun Zhang, Xun Zhang
      In order to investigate the influences of elastic bearings on ground vibrations induced by trains traversing a bridge, a numerical model was established based on the combination of train/track/bridge and pier/pile/soil subsystems. The elastic bearings in the train/track/bridge subsystem were simulated by a spring-dashpot element. The two subsystems were linked by the bearing reaction forces, and the whole model was calculated in the time domain. The numerically computed ground vibrations were compared with measured ones to validate the model. On this basis, the influences of elastic bearings on train, bridge and ground responses were discussed. Results show that the dynamic responses of the train are hardly affected, while the dynamic responses at the pier top and on the ground are clearly attenuated in the frequency band above 40Hz. Some increments in the frequency range 8–30Hz can be observed around the eigenfrequency of the main girder-elastic bearing system. The laws of bearing stiffness influences on ground vibrations were similar for different stiffnesses of the elastic bearings. Within a distance of 15m from the bridge, elastic bearings with stiffnesses of 2400, 2000 and 1600MN/m can reduce ground vibrations. However, at locations more than 22.5m from the bridge, ground vibrations may be close to or even a little larger than those of the rigid bearing case. When the elastic bearing has a stiffness of 1200MN/m, ground vibrations are clearly decreased at all locations.


      PubDate: 2016-03-31T09:30:02Z
       
  • A new analytical approach to reconstruct the acceleration time history at
           the bedrock base from the free surface signal records
    • Abstract: Publication date: June 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 85
      Author(s): V.R. Feldgun, Y.S. Karinski, D.Z. Yankelevsky, A.V. Kochetkov
      Acceleration time histories of earthquake events are typically measured in seismic stations that are placed close to the soil top surface. These acceleration records are often used as input data for seismic analysis. It may be used for base excitation in seismic analysis of above ground structures with shallow foundations.. However it may not be used for seismic analysis of underground structures, or even for above ground buildings with deep foundations and several underground stories. The required base excitation data of the latter should have been measured below the top surface, at a level that may be determined according to the specific analyzed building geometry or at the bedrock below. If the acceleration time history at the bedrock would have been known, the seismic wave propagation through the soil medium, from the bedrock towards the top surface, could have been carried out and the base excitation of the buried structure could be determined. Since there is no data on the acceleration time history at the bedrock, and the only given data is the acceleration records at the top surface, the goal of this paper is to provide an exact reverse analysis procedure to determine the unknown acceleration time history at the bedrock that would exactly produce the measured acceleration time history at the top surface. Once this goal is achieved, seismic analysis of buried structures may be carried out with the determined acceleration record at the bedrock as input. This paper presents an analytical exact solution of the inverse problem for determination of the acceleration, velocity and displacement time histories at the bedrock base of a layered geological medium that are compatible with the given acceleration record at the soil top surface. This new proposed method is based on analytical solutions of the initial-boundary value problems of the linear wave equation in the case of a layered medium. The relationship between waves in one layer and waves in another adjacent layer is derived considering the continuity of stresses and displacements at the common interface between the layers. The efficiency and accuracy of the proposed method is demonstrated through several examples involving the nonstationary response of the free surface. The case of the San Fernando Earthquake is studied. Excellent agreement is achieved between the recorded free surface time history and the reconstructed signal. This excellent agreement is obtained due to the exact analytical method used in deriving the inverse problem solution. This exact analytical method allows one to obtain an acceleration (velocity/displacement) distribution along all the layers at any time.


      PubDate: 2016-03-25T05:41:52Z
       
  • Seismic analysis of underground tunnels by the 2.5D finite/infinite
           element approach
    • Abstract: Publication date: June 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 85
      Author(s): K.C. Lin, H.H. Hung, Judy P. Yang, Y.B. Yang
      A procedure for the seismic analysis of underground tunnels using recorded free-field earthquakes based on the 2.5D finite/infinite element approach is presented. The near and far fields of the half space are modeled by finite and infinite elements, respectively. Using the 1D wave theory, the nodal force and displacement on the near-field boundary are computed for each spectral frequency of the earthquake. Then, equivalent seismic forces are computed for the near-field boundary for the earthquake spectrum. By assuming the soil-tunnel system to be uniform along the tunnel axis, the 2.5D approach can account for the wave transmission along the tunnel axis, which reduces to the 2D case for infinite transmission velocity. The horizontal and vertical components of the 1999 Chi-Chi Earthquake (TCU068) are adopted as the free-field motions in the numerical analysis. The maximal stresses and distribution patterns of the tunnel section under the P- and SV-waves are thoroughly studied by the 2.5D and 2D approaches, which should prove useful to the design of underground tunnels.


      PubDate: 2016-03-25T05:41:52Z
       
  • Seismic ground response at Lotung: Hysteretic elasto-plastic-based 3D
           analyses
    • Abstract: Publication date: June 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 85
      Author(s): A. Amorosi, D. Boldini, A. di Lernia
      This paper presents a non-linear finite element study to back-interpret the free field seismic response recorded at the Lotung Large-Scale Seismic Test site. The study is carried out in the time domain by the Finite Element (FE) code PLAXIS 3D, considering the vertical wave propagation of both the horizontal components of motion. The non-linear soil behaviour is simulated through a constitutive model, the Hardening Soil model with Small-Strain Stiffness (HSsmall), capable of describing the cyclic response of the material at different strain levels. In the paper, the constitutive response of the HSsmall model is firstly investigated through numerical simulations of strain-controlled cyclic shear tests under single and multi-directional conditions at low strain levels. Then, it is adopted to back-analyse the recorded free field seismic response, comparing the FE numerical results to the in-situ down-hole and surface signals recorded during two earthquakes occurred on May 20th and July 17th 1986, characterized by different peak ground accelerations.


      PubDate: 2016-03-25T05:41:52Z
       
  • On planar seismic wavefront modeling for estimating rotational ground
           motions: Case of 2-D SH line-source
    • Abstract: Publication date: June 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 85
      Author(s): Varun K. Singla, Vinay K. Gupta
      At large hypocentral distances, it is convenient to approximate the curved transient seismic wavefronts as planar to estimate rotational ground motions from the single-station recordings of translational ground motions. In this paper, we investigate whether and when this approximation, referred to as the ‘plane-wave’ approximation, can be considered adequate close to the source. For this, we consider a simplistic source model comprising a two-dimensional, kinematic shear dislocation SH line-source buried in a homogenous, elastic half-space and assume this to be an equivalent representation of a finite-sized fault. The ‘plane-wave’ rotational motion is then synthesized from the exact translational motion solution to the assumed model and compared with the exact rotational motion solution for this model. The comparison between the two sets of rotational amplitudes in frequency domain suggests that the plane-wave approximation may be adequate, when the wavelengths of the seismic waves are much smaller than the source depth. When this is not true, the plane-wave approximation is seen to underestimate the Fourier amplitudes close to the source by several orders, particularly when the fault planes are vertically oriented. A similar comparison in the time domain indicates that a severe underestimation may also occur when the source rise time is longer than the shear-wave arrival time at the epicenter. Significant discrepancies are also observed between the waveforms of the exact and plane-wave rotational motions.


      PubDate: 2016-03-25T05:41:52Z
       
  • Challenges associated with site response analyses for soft soils subjected
           to high-intensity input ground motions
    • Abstract: Publication date: June 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 85
      Author(s): Shawn C. Griffiths, Brady R. Cox, Ellen M. Rathje
      Nonlinear site response analyses are generally preferred over equivalent linear analyses for soft soil sites subjected to high-intensity input ground motions. However, both nonlinear (NL) and equivalent linear (EQL) analyses often result in large shear strain estimates (3–10%) at soft sites, and these large strains may generate unusual characteristics in the predicted surface ground motions, such as irregular time histories and atypical spectral shapes. One source of unusual ground motion predictions may be attributed to unrealistically low shear strengths implied by commonly used modulus reduction curves. Therefore, modulus reduction and damping curves can be modified at shear strains greater than approximately 0.1% to provide a more realistic soil model for site response. However, even after these modifications, nonlinear and equivalent linear site response analyses still may generate unusual surface acceleration time histories and Fourier amplitude spectra at soft soil sites when subjected to high-intensity input ground motions. In this study, we use equivalent linear and nonlinear 1D site response analyses for the well-known Treasure Island site to demonstrate challenges associated with accurately modeling large shear strains, and subsequent surface response, at soft soil sites.


      PubDate: 2016-03-21T09:09:31Z
       
 
 
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