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Journal Cover Soil Dynamics and Earthquake Engineering
  [SJR: 1.482]   [H-I: 45]   [12 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0267-7261
   Published by Elsevier Homepage  [2969 journals]
  • Mitigation of reverse faulting deformation using a soil bentonite wall:
           Dimensional analysis, parametric study, design implications
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): Meysam Fadaee, Pedram Ezzatyazdi, Ioannis Anastasopoulos, George Gazetas
      Recent major seismic events, such as the Chi-Chi (1999) and the Wenchuan (2008) earthquakes occurred in Taiwan and China, have offered a variety of case histories on the performance of structures subjected to reverse faulting–induced deformation. A novel faulting mitigation method has recently been proposed, introducing a soft deformable wall barrier in order to divert the fault rupture away from the structure. This can be materialized by constructing a thick diaphragm-type soil bentonite wall (SBW) between the structure and the fault rupture path. The paper investigates the key parameters in designing such a SBW, aiming to mitigate the fault rupture hazard on shallow foundations. The paper employs a thoroughly validated finite element analysis methodology to explore the efficiency of a weak SBW barrier in protecting slab foundations from large tectonic deformation due to reverse faulting. A dimensional analysis is conducted in order to generalize the validity of the derived conclusions. The dimensionless formulation is then used to conduct a detailed parametric study, exploring the effect of SBW thickness w/H, depth H SBWl /H, and shear strength τ soil /τ SBW , as well as the bedrock fault offset h/H, foundation surcharge load q/ρgB, and fault outcrop location s/B. It is shown that the wall thickness, depth, and shear strength should be designed on the basis of the magnitude of the bedrock fault offset, the location of the fault relative to the structure, and the shear strength of the soil. The efficiency of the weak barrier is improved using lower strength and stiffness material compared to the alluvium. A simplified preliminary design methodology is proposed, and presented in the form of a flowchart.


      PubDate: 2016-08-26T10:40:48Z
       
  • Earthquake response of solitary slender freestanding intake towers
    • Abstract: Publication date: November 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 90
      Author(s): Mohammad Alembagheri
      Earthquake response of solitary slender intake towers is investigated considering an idealized hollow intake tower with its circular footing submerged in water. The tower is studied in anchored (fixed base) and unanchored (freestanding) states placed on undeformable soil foundation. The water-structure interaction is modeled by the Eulerian-Lagrangian approach, using the pressure-based elements for the water and the displacement-based elements for the structure. The only source of nonlinearity is the contact at the base joint between the tower's footing and the ground. This contact is modeled using Coulomb friction model which allows the tower to slide and uplift. The system is three-dimensionally analyzed using finite element method under static and dynamic earthquake loads. A detailed parametric study is conducted to assess the importance of system characteristics including surrounding and inside water levels, ratio of tower height to footing radius, base joint friction coefficient, water compressibility, footing flexibility, and vertical ground motion.


      PubDate: 2016-08-26T10:40:48Z
       
  • Shake table testing of the dynamic interaction between two and three
           adjacent buildings (SSSI)
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): Hesham Aldaikh, Nicholas A. Alexander, Erdin Ibraim, Jonathan Knappett
      The dynamic interaction of adjacent buildings in cities and urban areas through the soil medium is inevitable. This fact has been confirmed by various analytical and numerical studies. However, very little research is available on the physical modelling of the Structure-Soil-Structure Interaction (SSSI) problem and its effect on the dynamics of adjacent structures. In this paper, a series of shaking table tests was conducted at the Earthquake and Large Structures Laboratory (EQUALS) at the University of Bristol to examine the effects of SSSI on the response of a model building when bordered by up to two other model buildings under dynamic excitation. The results indicated that depending on their height, the presence of one or two adjacent building could positively or negatively alter seismic power and peak acceleration responses of a building in comparison to when it is tested in isolation.


      PubDate: 2016-08-20T10:25:11Z
       
  • Numerical investigation of the effects of geometric and seismic parameters
           on liquefaction-induced lateral spreading
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): Omid Ghasemi-Fare, Ali Pak
      The lateral movement of a liquefiable soil layer on gentle slopes is the most visible and devastating type of liquefaction-induced ground failure. Recent earthquakes have shown that this phenomenon causes severe damages to coastal structures, pier of the bridges and life-lines by exerting large lateral forces on the structures. In this paper coupled dynamic field equations of extended Biot's theory with u-p formulation are used for simulating the phenomenon and the soil behavior is modeled by a critical state two-surface plasticity model for sands. Furthermore, in this study variation of permeability coefficient during liquefaction is taken into account. The permeability coefficient is related to variation of the excess pore water pressure ratio. At first, two centrifuge tests on liquefiable sand which have gently inclined ground surfaces with different conditions are simulated and numerical results are compared with experimental observations. These comparisons showed that numerical simulations have very good consistency with experimental observations in modeling of excess pore pressures, lateral displacements, and surface settlements. After validation, the effects of different factors such as ground slope, thickness of the liquefiable layer, soil relative density, maximum acceleration of dynamic loading, frequency of input motion and number of load cycles are investigated on the amount of lateral displacement. At the end, by using the results of the conducted extensive parametric study, a new relation is proposed for estimating the magnitude of maximum lateral displacement. Comparison of the results of this equation with experimental records, field observations and other empirical relations shows the advantage of this equation over other previously proposed relations.


      PubDate: 2016-08-20T10:25:11Z
       
  • The effect of grain size on Gmax of a demolished structural concrete: A
           study through energy dispersive spectroscopy analysis and dynamic element
           testing
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): H. He, K. Senetakis
      Recycled concrete aggregate (RCA) composed of demolition-crushed structural concrete is a promising material in geotechnical engineering applications, for example, as a backfill in retaining walls or as an embankment fill and pavement construction material. Due to the presence of cement mortar component, RCA has a lower unit weight than that of typical soils, thus its use may be considered beneficial in engineering infrastructures with a demand in the reduction of settlements or lateral earth pressures. In this study, a set of torsional resonant column and bender element tests were carried out on uniform fractions of a recycled concrete aggregate with origin from New South Wales, Australia, with varying the mean grain size. The created in the laboratory samples, were prepared in a dry state and tested under isotropic conditions of the confinement varying the effective confining stress from 25 to 800kPa in a resonant column and in a triaxial apparatus with embedded piezo-element inserts with a particular focus on the elastic stiffness Gmax. The results showed that the sensitivity of Gmax to pressure increased with decreasing mean grain size. This observed trend was attributed, partly, to the higher cement mortar component for fractions with a smaller grain size. The different composition of the fractions was verified through Scanning Electron Microscope - Energy Dispersive Spectroscopy (SEM-EDS) analysis in particular quantifying the ratio of Silicon over Calcium contents. The performance of expressions proposed in the literature for the prediction of Gmax of sands and gravels, was rigorously evaluated by means of measured against predicted elastic stiffness for all the fractions as well as by means of the state parameter for a particular RCA fraction.


      PubDate: 2016-08-20T10:25:11Z
       
  • Ap/Vp specific inelastic displacement ratio for the seismic response
           estimation of SDOF structures subjected to sequential near fault pulse
           type ground motion records
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): Cengizhan Durucan, Ayşe Ruşen Durucan
      This research study is focused on an improved statistical equation proposed to estimate the inelastic displacement ratio, C1, of structures subjected to sequential (pre-shock, main shock, after shock) pulse type near fault (NF) ground motions. Proposed equation considers the effects of fundamental vibration period of the structure, T, lateral strength ratio, R, and frequency content of the design earthquake on the variation of the response. Frequency content of the design earthquake, represented by the Ap/Vp ratio (i.e. ratio of peak ground acceleration (Ap) to peak ground velocity (Vp)), is a function of the earthquake magnitude, distance to fault, faulting mechanism and site class. In scope of the study statistical analyses were conducted to develop a simple and accurate statistical equation to estimate the C1 of structures subjected to sequential pulse type NF ground motions. From the results of the study it was observed that the C1 values obtained from the proposed equation are, generally, in good agreement with the calculated exact results. Also, the C1 and T relationships were plotted together with those of a former study to clearly show the detrimental effect of the sequential ground motion loading in terms of amplified displacement demands.


      PubDate: 2016-08-16T10:12:05Z
       
  • Gorkha (Nepal) earthquake of April 25, 2015: Actual damage, retrofitting
           measures and prediction by RVS for a few typical structures
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): Sekhar Chandra Dutta, Sanket Nayak, Gokul Acharjee, Sarat Kumar Panda, Pranab Kumar Das
      This study is an attempt to underline the lack of preparedness and the nature of immediate further measures to be taken for facing a moderate earthquake in Indian subcontinents. Surprisingly, moderate to severe damage was noticed in structures located in hundreds of kilometres away from epicentre during last Gorkha earthquake. In this context, the present study makes an effort to validate a proposed modified rapid visual screening schemes for low cost houses frequently available in India. This may be used extensively for quick vulnerability assessment of a locality. Examples of retrofitting measures for typical buildings presented in this study may be useful for upgrading the valuable structures. Thus this study may be helpful for quick vulnerability assessment and adopting retrofitting measures for identified structures for earthquake prone developing countries.


      PubDate: 2016-08-16T10:12:05Z
       
  • Influence of coefficient of uniformity and base sand gradation on static
           liquefaction of loose sands with silt
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): Mehmet Murat Monkul, Ehsan Etminan, Aykut Şenol
      When occurred on site static or flow type liquefaction could result in catastrophic consequences due to its sudden occurrence with large strains. Presented here is an experimental study based on monotonic undrained triaxial compression tests conducted on three clean sands and their mixtures with three different non-plastic silts at three different fines contents (≤25%). The results demonstrate that base sand gradation has significant influence on the static liquefaction potential of clean and silty sands. It was observed that clean sands become more liquefiable as their mean grain size got smaller and/or they became more uniform. However, it was found that the order of liquefaction resistance of the same base sands were reversed when they were mixed with silt (i.e. resulting silty sands become more liquefiable as the mean grain size of base sand got larger and/or base sand became relatively well graded). Possible reason for such a reversed behavior was hypothesized and then experimentally justified with extra tests. It was also found that the influence of base sand gradation on static liquefaction of loose specimens was most significant at low fines content (e.g. 5%) and almost erased at relatively high fines contents (e.g. 25%). In the last part of the study, the relationship between the normalized peak deviator stress (qpeak/σ‘3c) and coefficient of uniformity (CU) is discussed. It was shown that unlike clean sands, for which liquefaction potential decreases with increasing CU, the liquefaction potential of sand-silt mixtures reconstituted in the laboratory increases with increasing coefficient of uniformity (i.e. technically as they became more well graded). Two equations were proposed to represent the discussed relationship between qpeak/σ‘3c and CU; one for stable and temporarily liquefied specimens, the other for liquefied specimens. Finally, the applicability of these equations to other types of silty sands in literature was shown.


      PubDate: 2016-08-16T10:12:05Z
       
  • Inelastic seismic energy spectra for soft soils: Application to Mexico
           City
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): Pablo Quinde, Eduardo Reinoso, Amador Terán-Gilmore
      Earthquake databases are not sufficiently complete, particularly for soft soils. Also, there are few and oversimplified formulations that allow an understanding on the relation that exists between the elastic and inelastic energy demands for this type of soils. A study on energy reduction factors aimed at establishing inelastic input and hysteretic energy spectra for narrow-banded motions is presented. Unlike previous works, in this study elastic input energy spectra are used as input for energy functional forms that allow the formulation of inelastic energy spectra. For this purpose, over 250 seismic records recorded in soft soils are used. The energy reduction factors yield inelastic energy spectra that capture in a reasonable manner the energy content of narrow-banded ground motions, and yield a better characterization of inelastic energy demands.


      PubDate: 2016-08-16T10:12:05Z
       
  • The effect of boundary conditions, model size and damping models in the
           finite element modelling of a moving load on a track/ground system
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): J.Y. Shih, D.J. Thompson, A. Zervos
      An investigation is presented of the use of finite element models in the time domain to represent a load moving on a railway track on a flexible ground. A systematic study is carried out to compare different sizes and shapes of finite element mesh, different boundary conditions intended for suppressing reflections from the truncated model boundaries, and different models of soil damping. The purpose is to develop guidance to assist in selecting appropriate finite element models for moving load problems. To prevent reflections from the boundaries of the finite domain two approaches are compared. A 40m radius hemispherical finite element mesh has been used first with infinite elements around the perimeter. This approach gives good results for a point harmonic load at the centre of the domain but some problems are highlighted when it is used for moving load calculations. An alternative approach has therefore been investigated based on a cuboid mesh. The base was fixed to prevent rigid-body motions of the model and, rather than use infinite elements at the sides, these were also fixed. It is shown that, provided that a suitable damping model is used, the spurious reflections from the sides of the model can be suppressed if the model is wide enough. On the other hand, if infinite elements are used, the calculations are found to be considerably more costly with little added benefit. Different models of soil damping are also compared. It is shown that a mass-proportional damping model gives a decay with distance that is independent of frequency, making it particularly suitable for this application. The length of model required to achieve steady state has been investigated. For a homogeneous half-space it is found that the required length increases considerably in the vicinity of the critical speed, up to 130m in the present example, whereas for the layered ground a more modest length is sufficient for all speeds.


      PubDate: 2016-08-11T09:42:32Z
       
  • Seismic performance of square, thin-walled steel tube/bamboo plywood
           composite hollow columns with binding bars
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): Jing Zhou, Weifeng Zhao, Kai Tang, Wanxi Peng
      A thin-walled steel tube/bamboo plywood composite hollow column with binding bars (SBCCB) was developed using transverse binding bars to reinforce a thin-walled steel tube and bamboo plywood composite hollow column. Low reversed cyclic loading tests were performed on 9 SBCCB specimens to observe the damage process and morphology in the SBCCBs. The effects of the slenderness ratio, the net cross-sectional area of the bamboo plywood, the assembly patterns of the cross sections, and the binding bars on the stress and seismic performance were investigated. The results show that the main failure modes of the SBCCBs were cracking of different adhesion interfaces at the base of the column and fracturing of the bamboo plywood. The cross-sectional assembly pattern has a significant effect on the failure modes; increasing the cross-sectional area and the slenderness ratio of the composite column will dramatically improve the seismic performance of the SBCCBs. SBCCBs have excellent elastic deformation and seismic energy consumption characteristics. The binding bars ensure the integrity of the specimen and inhibit the failure of the adhesion interface at the base of the column. Finally, based on the measurement of the axial pressure and the stress-strain curve within elastic range of the composite columns, a simplified mechanical model and a calculation method for bearing capacity was formulated. The calculation values of bearing capacity agree well with the experimental ones, and calculation method can be used to provide guidance for engineering applications of a SBCCB.


      PubDate: 2016-08-11T09:42:32Z
       
  • A new series solution method for two-dimensional elastic wave scattering
           along a canyon in half-space
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): Yu Yao, Tianyun Liu, Jian-min Zhang
      This paper presents a semi-analytical method for studying the two-dimensional problem of elastic wave scattering by surface irregularities in a half-space. The new method makes use of the member of a c-completeness family of wave functions to construct the scattering fields, and then applies equal but opposite tractions to those of the foregoing constructed scattering fields on the horizontal surface of the half-space to produce additional scattering fields. These additional scattering fields are a series of Lamb's solutions. Thus the whole scattering field constructed in the series automatically satisfies the Navier equations, the condition of zero traction on the half-space surface, and the radiation boundary conditions at infinity. Using the traction-free conditions along the canyon surface, the coefficients of the series solutions are determined via a least-squares method. For incident P, SV, and Rayleigh waves, the numerical results are presented for the scattering displacements in the vicinity of a semi-circular canyon in the half-space.


      PubDate: 2016-08-11T09:42:32Z
       
  • Detailed site effect estimation in the presence of strong velocity
           reversals within a small-aperture strong-motion array in Iceland
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): Sahar Rahpeyma, Benedikt Halldorsson, Christian Olivera, Russell A. Green, Sigurjón Jónsson
      The rock site characterization for earthquake engineering applications in Iceland is common due to the easily exposed older bedrock and more recent volcanic lava rock. The corresponding site amplification is generally assumed to be low but has not been comprehensively quantified, especially for volcanic rock. The earthquake strong-motion of the M w 6.3 Ölfus earthquake on 29 May 2008 and 1705 of its aftershocks recorded on the first small-aperture strong-motion array (ICEARRAY I) in Iceland showed consistent and significant variations in ground motion amplitudes over short distances (<2km) in an urban area located mostly on lava rock. This study analyses the aftershock recordings to quantify the local site effects using the Horizontal to Vertical Spectral Ratio (HVSR) and Standard Spectral Ratio (SSR) methods. Additionally, microseismic data has been collected at array stations and analyzed using the HVSR method. The results between the methods are consistent and show that while the amplification levels remain relatively low, the predominant frequency varies systematically between stations and is found to correlate with the geological units. In particular, for stations on lava rock the underlying geologic structure is characterized by repeated lava-soil stratigraphy characterized by reversals in the shear wave velocity with depth. As a result, standard modeling of HVSR using vertically incident body waves does not apply. Instead, modeling the soil structure as a two-degree-of-freedom dynamic system is found to capture the observed predominant frequencies of site amplification. The results have important implications for earthquake resistant design of structures on rock sites characterized by velocity reversals.


      PubDate: 2016-08-11T09:42:32Z
       
  • Three-dimensional track-ballast interaction model for the study of a
           culvert transition
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): J.N. Varandas, P. Hölscher, M.A.G. Silva
      Transition zones corresponding to the passage from railway tracks on embankments to settlement free structures are frequently problematic for maintenance. Changing stiffness of the track and differential settlements are main causes for the degradation of tracks and foundations at transitions. This paper concentrates on a railway passage over a box-culvert, where significant settlements were observed in the transition zones. Previous research using a Winkler type model showed that this cannot be explained by ballast compaction due to trains passage only. The paper presents a 3-D model. It describes the behaviour of the rail track, ballast, embankment and approach slabs. This calculation shows that the stress in the soil close to the approach slabs exceeds the strength of the ballast. This leads to rolling of particles on the approach slab and explains the differences between the Winkler type model results and the observed settlements.


      PubDate: 2016-08-11T09:42:32Z
       
  • Seismic control of irregular multistory buildings using active tendons
           considering soil–structure interaction effect
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): Ebrahim Nazarimofrad, Seyed Mehdi Zahrai
      Much research has been conducted in recent decades on structural control to improve the performance of different towers and high-rise buildings against severe earthquakes and strong winds. Most studies on building vibration control have been considered just two-dimensionally using shear frame models. In reality, most of the buildings might have irregular plans and thus experience torsion when subjected to earthquakes. Such torsion would further increase the structural response. On the other hand, some buildings are located on soft soil that would trigger the soil-structure interaction (SSI) effects required to be considered for design purposes. The main dynamic behavior parameters like natural frequencies, damping ratios and mode shapes would depend on construction site conditions and thus the SSI effects must be taken into account for buildings on soft soil. In this paper, a mathematical model is developed for calculating the seismic response of an irregular multi-story building equipped with active tendons. The SSI effect is then introduced by changing structure mass, stiffness and damping matrices. The model is employed to obtain the seismic response of 10-story buildings using active tendon with LQR algorithm. The building is modeled as a structure composed of members connected by rigid floor diaphragms with three degrees of freedom at each story; i.e. lateral displacements in two perpendicular directions and a rotation with respect to a vertical axis. Results showed that active tendons have low effects on the reduction of structural response when the building has been located on soft soils.


      PubDate: 2016-08-11T09:42:32Z
       
  • An energy flow study of a double-deck tunnel under quasi-static and
           harmonic excitations
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): Arnau Clot, Jordi Romeu, Robert Arcos
      This paper presents a comparison between the vibration energy flow radiated by a double-deck tunnel and the one radiated by a simple tunnel when both are excited by constant or by harmonic moving loads. For both cases, the radiated energy is computed using a three-dimensional semi-analytical model of the system. The total energy radiated upwards is presented for a wide range of load speeds, when a constant moving load is considered, and for a wide range of excitation frequencies, when the excitation is a harmonic moving load. Significant differences have been obtained, first, for constant loads moving at very high speeds and, second, for harmonic loads moving at typical speeds for underground trains.


      PubDate: 2016-08-11T09:42:32Z
       
  • Procedure for selecting and modifying earthquake motions to multiple
           intensity measures
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): Richard J. Armstrong
      A new ground motion selection and modification procedure is presented that selects a set of ground motions to capture multiple intensity measure targets. The ground motion selection and modification procedure involves selecting a set of candidate ground motions scaled to a conditioning intensity measure that is subsequently trimmed down using a semi-automated selection process to reach a final set that satisfies statistical considerations. The new procedure is relatively straightforward to implement using common tools and knowledge yet is still based on the principles of conditioning and on aspects of previously-developed selection and modification procedures. A single example is provided to demonstrate the use of these concepts to ground motion development.


      PubDate: 2016-08-11T09:42:32Z
       
  • 2D non-linear seismic response of the Dinar basin,TURKEY
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): H. Khanbabazadeh, R. Iyisan, A. Ansal, M.E. Hasal
      Local geological conditions generate significant amplification of ground motion and concentrated damage during earthquakes. The highly concentrated damages at the edges of the Dinar basin during occurred earthquakes at regions close to rock outcrop bring up the effect of the inclined bedrock effect on the dynamic behavior of the basin with 2D geometry. In this study, first the idealized 2D model of the basin based on the results of the underground explorations and geologic investigations is proposed. Results show that Dinar basin has an asymmetric 2D geometry with two different bedrock angles at edges. Then, a numerical study using finite difference based nonlinear code which utilizes appropriate static and dynamic boundary conditions, and includes hysteresis damping formulation based on the user defined degradation curves is conducted using real earthquake motions of different strength and frequency content. The constructed model is subjected to the collection of 16 earthquakes with different PGA's of 0.1, 0.2, 0.3 and 0.4g, four motions for each PGA. It was seen that the dynamic behavior of the basin is broadly affected by the two dimensional bedrock. The results indicates the higher effect of the 6° bedrock inclination at east part on the amplification with respect to the steeper 20° bedrock slope at the west. Also, the results show the insignificant effect of the bedrock at the depth more than 150m on the amplification of the east edge. While the effect of the 6° bedrock angle at the east part continues until 1500m from the outcrop, it affects the amplification until 700m from the outcrop at the west part with 20° bedrock angle.


      PubDate: 2016-08-11T09:42:32Z
       
  • Boundary reaction method for nonlinear analysis of soil–structure
           interaction under earthquake loads
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): Jae-min Kim, Eun-haeng Lee, Sang-hoon Lee
      This paper presents a boundary reaction method (BRM) for nonlinear time domain analysis of soil–structure interaction (SSI) under incident seismic waves. The BRM is a hybrid frequency–time domain method, but it removes global iterations between frequency and time domain analyses commonly required in the hybrid approach, so that it operates as a two-step uncoupled method. Specifically, the nonlinear SSI system is represented as a simple summation of two substructures as follows: (I) wave scattering substructure subjected to incident seismic waves to calculate boundary reaction forces on the fixed interface boundary between a finite nonlinear structure-soil body and an unbounded linear domain; and (II) wave radiation substructure subjected to the boundary reaction forces in which the nonlinearities can be considered. The nonlinear responses in the structure–soil body can be obtained by solving the radiation problem in the time domain using a general-purpose nonlinear finite element code that can simulate absorbing boundary conditions, while the boundary reaction forces can be easily calculated by solving the linear scattering problem by means of a standard frequency domain SSI code. The BRM is verified by comparing the numerical results obtained by the proposed BRM and the conventional frequency-domain SSI analysis for an equivalent linear SSI system. Finally, the BRM is applied to the nonlinear time-domain seismic analysis of a base-isolated nuclear power plant structure supported by a layered soil medium. The numerical results showed that the proposed method is very effective for nonlinear time-domain SSI analyses of nonlinear structure-soil system subjected to earthquake loadings.


      PubDate: 2016-08-11T09:42:32Z
       
  • Soil-pile-structure kinematic and inertial interaction observed in
           geotechnical centrifuge experiments
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): Mahmoud N. Hussien, Tetsuo Tobita, Susumu Iai, Mourad Karray
      This paper reports the results of a series of centrifuge tests examining dynamic responses of single and 3×3 grouped piles embedded in sand and supporting SDOF and 2DOF structures. A total of 7 model tests were conducted with the centrifugal acceleration of 40 g. Each model was subjected to 12 sinusoidal waves with constant acceleration amplitude and varying frequencies. The results of the tests indicate that pile-head motion is dominated by two sequential frequencies: a lower frequency (f SSI) where pile-head motion is substantially maximized and a higher one (f pSSI) where the response is minimized with respect to free field surface motion. These results confirm recent published numerical results on single piles supporting SDOF structures and generalize their findings to grouped piles supporting SDOF and 2DOF structures. The results show also strong mobilized kinematic interaction effect generating significant pile bending when the ground is excited at its resonant frequency. On the other hand, structural vibrations tend to impose large bending moments as the excitation frequency approaches the natural frequency of the coupled soil-pile-structure system. Distribution of pile bending moments in the group is found to be a function of the pile position and the excitation frequency. In contrast to inner piles having the greatest kinematic bending moments, outer piles have a more pronounced inertial ones.


      PubDate: 2016-08-11T09:42:32Z
       
  • Computation of degradation factors of p-y curves in liquefiable soils for
           analysis of piles using three-dimensional finite-element model
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): Asskar Janalizadeh Choobbasti, Ali Zahmatkesh
      This paper presents a procedure to compute the values of degradation factors of p-y curves in the pseudo-static analysis of piles in liquefiable soils. Three-dimensional finite-element model was used for the computation of p and y values using OpenSees computer package. The piles were modeled using beam-column elements and elastic section. The soil continuum was modeled using brick elements and a two-surface plasticity model. By comparing the results of models in two cases of liquefiable and non-liquefiable, values of degradation factors were obtained. Validation of the degradation factors computed was conducted through the centrifuge test results. The simulation results showed a similar trend between degradation factor variation in different densities and sands. With increasing depth, the degradation factor increased. By comparing the results of pseudo-static analysis with the centrifuge test results, it was concluded that the use of the p-y curves with computed degradation factors in liquefiable sand gave reasonable results.


      PubDate: 2016-08-11T09:42:32Z
       
  • Assessment of seismic liquefaction potential based on Bayesian network
           constructed from domain knowledge and history data
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): Ji-Lei Hu, Xiao-Wei Tang, Jiang-Nan Qiu
      Prediction of seismic liquefaction is difficult due to the uncertainties and complexity of multiple related factors. Bayesian network is a just right effective tool to deal the problem because of merging multiple source information and domain knowledge in a consistent system, reflecting and analyzing the interdependent uncertain relationships between variables. This paper used two ways to construct generic Bayesian network models with twelve significant factors of seismic liquefaction, of which the first model is constructed only by interpretive structural modeling and causal mapping approach for incomplete data contained huge missing values. Another one is constructed by combining K2 algorithm and domain knowledge for complete data. Compared with artificial neural network and support vector machine using 5-fold cross-validation, the two Bayesian network models provided a better performance, and the second Bayesian network model is slightly better than the first one. This paper also offers a sensitivity analysis of the input factors. In the twelve variables, standard penetration test number, soil type, vertical effective stress, depth of soil deposit, and peak ground acceleration have more significant influences on seismic liquefaction than others. Our results suggest that the Bayesian network is useful for prediction of seismic liquefaction and is simple to perform in practice.


      PubDate: 2016-08-11T09:42:32Z
       
  • Wave propagation with energy diffusion in a fractal solid and its
           fractional image
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): Gerd Gudehus, Asterios Touplikiotis
      Crucial features of seismograms and spectra with small amplitudes are explained by means of fractality and fractional calculus. Wave propagations in the elastic range of porous solids imply precursors and followers of coherent waves. They result from a non-local diffraction via force chains which is called energy diffusion. Such phenomena are captured by fractional wave equations which are deduced by means of an elastic energy and the balance of momentum for random fractal ensembles. Theoretical propagations imply precursors which were similarly observed with bender elements, and a rate of dissipation nearly proportional to the kinetic energy which suits to resonant column test results. A novel three-dimensional fractional Dirichlet-Green function implies primary and secondary wave crests with speed and alignment which do not depend on the fractal dimension. Power spectra in the dislocation-free far-field of seismogeneous chain reactions and impacts tend to a fractality-dependent power law with a peak-like cutoff, both theoretically and observed, therein a modified Huygen’s principle is employed. Limitations are discussed and possible extensions are indicated.


      PubDate: 2016-08-11T09:42:32Z
       
  • Experimental evaluation of vulnerability for urban segmental tunnels
           subjected to normal surface faulting
    • Abstract: Publication date: October 2016
      Source:Soil Dynamics and Earthquake Engineering, Volume 89
      Author(s): Majid Kiani, Abbas Ghalandarzadeh, Tohid Akhlaghi, Mohammad Ahmadi
      Faulting is one type of permanent ground displacement (PGD); tunnels are at the risk of damage when they are susceptible to faulting. The present study proposes an experimental approach to create the fragility curves for shallow segmental tunnels in alluvial deposits subjected to normal surface faulting. Centrifuge testing was carried out in order to achieve this purpose. The proposed approach allows evaluation of new fragility curves considering the distinctive features of tunnel geometry and fault specifications. The comparison between the new fragility curves and the existing empirical curves was discussed as well. Compared to tunnels in rock, tunnels in alluvial deposits are more susceptible to failure because of different mechanisms of collapse into tunnel at large exerted PGD.


      PubDate: 2016-08-11T09:42:32Z
       
  • 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
       
  • 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
       
 
 
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