Kinematic Interaction Effects Research Articles

Effects of kinematic and inertial interaction on seismic responses of pile-structure system in liquefiable and non-liquefiable deposits

Numerical simulation models for pile group-superstructure in liquefiable and non-liquefiable sites were established. The validity and reliability of the numerical model are verified by the shaking table test results. Based on the cross-correlation analysis of superstructure acceleration-pile bending moment and soil displacement-pile bending moment obtained from the tests, the coupling law of kinematic and inertial interaction and its influence on pile failure modes were discussed combined with the numerical simulation results. The results shown that the effect of kinematic interaction on piles were greater than that of inertial interaction in both types of sites, but coupling mechanisms of kinematic and inertial interaction were different. For the liquefiable site scenario, the middle part of piles was prone to bending failure and the kinematic interaction was the main reason for it. For the non-liquefiable site scenario, the inertial interaction had an obvious influence on the pile failure occurred at the pile top. The results of parameter analysis shown that the mass of the superstructure was the most important parameter of inertial interaction in the liquefiable site. Parameters of inertial interaction would affect the vibration of the superstructure in the non-liquefiable site, but the influence on pile bending moments was not obvious.

Contribution of the rotational kinematic interaction to the seismic response of monopile-supported offshore wind turbines

This paper presents a study on the role of kinematic interaction effects on the seismic response of large monopile-supported offshore wind turbines. For this purpose, a finite element substructuring model is used to analyse the behaviour of three reference wind turbines with rated powers of 5, 10 and 15 MW founded on several soil profiles and subjected to different accelerograms. The foundation response is computed through a continuum model which includes soil–structure interaction. The effects of inertial and kinematic soil–structure interaction on the system seismic response is evaluated also through comparisons with results corresponding to the infinitely rigid base condition. It is found that neglecting kinematic interaction factors could lead to underestimate the seismic response of large monopile-supported offshore wind turbines. The rotational kinematic interaction factor is shown to increase the OWTs seismic response.

Inertial and kinematic interactions of bridge‐pile group subjected to liquefaction induced lateral spreading: Large‐scale shaking table experiments

AbstractThis paper investigates the seismic bridge‐pile‐soil system failure mechanisms due to liquefaction‐induced lateral spreading. Two large‐scale shaking table tests were performed on pile groups with and without bridges in sloped liquefiable soils overlain by soil crust. The systems were subjected to a weak earthquake signal (Tabas 0.05 g) and a strong earthquake signal (Tabas 0.3 g). Their responses were recorded in terms of excess pore pressure, acceleration, and displacement time histories. The piles seismic failure mode and mechanism are described based on the obtained results. In addition, the inertial and kinematic interaction effects on the piles’ deflection were evaluated. The results demonstrated that the bridge had no significant effect on the seismic response of the pile‐soil system under weak earthquakes. Meanwhile, the test model without a bridge experienced more significant soil lateral displacement, and the saturated sand exhibited dilatant behavior, and amplified the acceleration peak response during the strong earthquake. Moreover, the liquefaction‐induced lateral spreading moved the vulnerable position of the pile group bridge system from the pier bottom to the pile head, which changed the failure mode of the pile head. The results also revealed that, compared with weak earthquake excitation, the kinematic effect was significantly enhanced, and the inertia effect was weakened during strong earthquakes. Moreover, the pile curvature during both weak and strong earthquakes was inversely proportional to the bridge inertial load.

The Filtering Effect of Pile Foundations in Clay

This paper reports the results of a series of centrifuge experiments exploring the dynamic response of pile foundations. The model tested in a centrifuge at 50g consisted of an isolated pile and two pile groups embedded in a kaolin clay, subjected to a sequence of quasi-sinusoidal waves with different amplitudes and frequencies. The results are back-analyzed through a two-step procedure. First, a one-dimensional ground response analysis is performed, in which the small-strain shear modulus is evaluated using data from air hammer tests, while a literature model is used to account for nonlinearity of soil behavior. Second, a three-dimensional finite-element analysis of the model foundations is carried out using the mobilized soil damping ratio and shear modulus determined from the previous step. The aforementioned procedure allowed to reproduce satisfactorily the response of the model foundations tested in the centrifuge, showing that the response of these models is strongly affected by the inertial oscillation of the cap connecting piles necessary to accommodate the measurement devices and to rigidly connect the piles’ heads of the groups. The same numerical model was then adopted to evaluate the change of seismic motion due to pure kinematic interaction effects by setting the pile cap mass equal to zero. This allowed to check the prediction capability of simplified methods of analysis for the evaluation of the base excitation of pile-supported structures. In addition, a number of issues related to the execution of centrifuge tests aimed at investigating the kinematic interaction between pile and soil are highlighted and discussed.

Evaluation of dynamic soil-structure interaction effects in buildings with underground stories using 1 g physical experimentation in a transparent shear laminar box

This article presents a study of the Dynamic Soil-Structure Interaction (DSSI) using physical reduced–scale models of a building under different configurations of above-ground and underground stories. Each model was tested in a laminar shear box with a transparent front side. This characteristic of the device makes it possible to visualize the soil particles during the test and acquire data from the soil-structure interaction in a direct and spatially continuous way. A shaking table, an array of 3 high–speed and high–resolution cameras and a tactile dynamic pressure sensor were used. Ricker wavelets, with a wide range of frequencies and amplitudes, were used to evaluate the transfer functions in the system and the seismic response of model. Kinematic interaction effects were evaluated using the Digital Image Correlation (DIC) technique. It is verified that the experimental system allows a detailed tracking of the dynamic interaction between the building and the surrounding soil. The results show the direct relationship between the frequency content of the input wavelet and the dynamic pressure distribution acting on the underground levels, and the increase of the building’s first vibrating period. In addition, it was found that the distribution and magnitude of the lateral soil thrust is dominated by the superstructure vibration, and not the ground movement. This relationship becomes more important as the slenderness of the building increases, i.e., as the rocking mode of vibration becomes more significant. Additionally, in the case of buildings with basements, our results suggest that the combination of the increased confinement, the interaction of the foundation in terms of motion compatibility and the vibrations transferred from the superstructure to the ground produces an invariable reduction in effective base motion, suggesting that neglecting the effects of DSSI would be a conservative assumption.

Seismic behaviour of piles in non-liquefiable and liquefiable soil

This paper investigates the nonlinear soil–pile–structure interaction employing three-dimensional nonlinear finite element models verified with the results of large-scale shaking table tests of model pile groups-superstructure systems. The responses of piles in both liquefiable and non-liquefiable soil sites to ground motion with varying intensities were evaluated considering both kinematic and inertial interaction. The calculated piles and soil responses agreed well with the responses measured during the shaking events. The numerical models correctly predicted the different pile deformation modes that were exhibited in the experiments. The finite element analysis was then employed to perform a parametric study to evaluate the kinematic and inertial effects on the piles' response, considering different ground motion Intensity and piles characteristics. It was found that the bending moment of piles in the liquefiable site increases significantly, compared to the non-liquefiable site, due to the loss of lateral support of the liquified soil, and the maximum bending moment occurs at the interface between the loose and dense sand layers. The inertial interaction contributes the most to the bending moments at the pile top and the interface between the top clay and liquefied loose sand layers. For piles with a larger diameter, the bending moment due to kinematic interaction increases significantly, and the bending moment distribution corresponds to short (rigid) pile behaviour. In addition, the piles at the saturated site displace laterally as a rigid body during strong ground motions because the pile base loses the lateral support due to the soil liquefaction. Finally, the kinematic interaction effect becomes more significant for piles with higher elastic modulus.

A modified simplified analysis method to evaluate seismic responses of subway stations considering the inertial interaction effect of adjacent buildings

A modified simplified analysis method is proposed in this paper to evaluate seismic responses of subway stations in dense urban environments. Based on the dynamic analysis of the underground structure-soil-adjacent building interaction (SSSI) model, the seismic response of subway station was distinguished as the kinematic interaction (KI) effect (induced by the free-field movement) and the inertial interaction (II) effect (induced by the vibration of adjacent building). In order to comprehensively and simply consider the KI and II effects, a modified model was established after simplifying the analytical solution of underground structural seismic response. Owing to acquiring the dynamic response via static modelling and calculation, the method proposed herein requires a shorter analysis time and incurs a lower cost. In addition, a typical subway station-soil-ground building system in an east city in China was selected as the case-history to verify the modified method and further evaluate its computational accuracy. The traditional response displacement method and dynamic time history analysis method were also conducted in simulation as a comparison method and standard method, respectively. The case study demonstrates that referencing the results obtained by the dynamic time history analysis method (D-M), the maximum story drift and maximum internal force (including bending moment, axial force and shear force) errors of the traditional response displacement method (T-M) reached −28% and −48%, respectively. Obviously, this method is dangerous in designing due to its smaller computing results. In contrast, the modified method (M-M) which can accurately reflect the impacts of adjacent buildings, is a more accurate and safer analysis method (two seismic response indexes of the modified method generally exceeded the actual values, and more gratifying is that the errors were less than 12%). Therefore, the modified simplified analysis method proposed is a higher accuracy, safer design, less time consumed, and faster analysis process method, which can be used to substitute the traditional method in the aseismic performance and dynamic response analysis of subway stations in dense urban environments.

Empirical evaluation of kinematic soil-structure interaction effects in structures with large footprints and embedment depths

Kinematic soil-structure interaction (SSI) effects cause foundation-level motions to deviate from free-field motions. Simplified procedures to account for kinematic SSI effects are available in design guidelines for regular buildings and have been calibrated for regular buildings with limited foundation size and depth of embedment. As a result, their application to structures with much larger foundation footprints and deeper embedment depths is questionable. Kinematic interaction effects can be used to reduce foundation-level ground motions relative to those specified in the free-field, and this can be cost-effective especially for structures with larger footprints and embedment depths. The objective of this study is to quantify the extent of deviations between the use of available simplified procedures and empirical data for a select group of structures with larger footprints and embedment depths. In this study, a dataset of earthquake motions recorded at the instrumented structures in Japan is used to evaluate kinematic SSI effects, which are quantified in terms of the transfer function and the ratio of response spectra between foundation motions and corresponding free-field motions. Transfer functions represent the ratio between the free-field and the foundation level of a structure motion in the frequency domain and can be obtained by dividing Power Spectral Density functions of foundation motion and corresponding free-field motion. Finally, these empirical functions are compared to the available simplified formulations such as the semi-empirical transfer function and the ASCE/SEI 41–17 recommended ratio of response spectra, and the results are presented in terms of residuals. The overall trends of residuals indicate that the current simplified procedures tend to overestimate the foundation motions in structures with large footprints and embedment depths, and the extent of overestimation is higher for the ratio of response spectra compared to transfer functions. Thus, in future studies, these simplified procedures should be revised for applications in structures with large footprints and embedment depths.

Evaluation on influences of inertial mass on seismic responses and structure-soil interactions of pile-soil-piers

This research is to assess the influences of the inertial mass from the girder on the dynamic characteristic, dynamic response, and structure-soil interaction of a pile-soil-pier subsystem in a scale-model of a cable-stayed bridge. Therefore, both connection configurations between the pile-soil-pier and girder, including the sliding and fixed connections, were designed to present various inertial mass from the superstructure delivered to the pile-soil-pier. The pile-soil-pier supported by a 3 × 3 pile-group in mixed soil placed in a shear box was tested using shaking tables. The dynamic characteristics, seismic responses, inertial interactions, and pile group effects of the pile-soil-pier between the sliding and fixed connections were analyzed under three input motions with different shaking amplitudes. These results showed that more inertial mass from the girder significantly increased the reinforcement strain and bending moment at the column bottom and pile top, displacement at the column top, inertial interaction effects, and pile group effects of the pile-soil-pier due to the sliding connection changing to the fixed connection. The inertial mass increment from the girder noticeably decreased the peak accelerations of the column of the pile-soil-pier when subjected to three input motions with different amplitudes. However, the inertial mass insignificantly affected the accelerations of the pile and free-soil. Therefore, the corresponding kinematic interaction effects were almost unaffected by the inertial mass. Additionally, the evident pile group effects were observed in the sliding and fixed connections between the pile-soil-pier and girder. The numerical model could approximately reproduce the macroscopic seismic responses of the pile-soil-piers with sliding and fixed connections and capture the typical response variations induced by the connection configuration change.

Implications of high-frequency decay parameter, “κ-kappa”, in the estimation of kinematic soil-structure interaction effects

In the present study, the difference between the peak seismic response measures recorded on building basements and those at nearby free-field conditions is studied by means of estimating the high-frequency spectral decay parameter, “κ” (known as “kappa”). Computation of “κ” is performed for selected accelerographic stations belonging to three strong motion networks, namely the Hellenic National Accelerographic Network (HNAN) in Greece, the Center for Engineering Strong Motion Data (CESMD) in California, USA and the Building Research Institute (BRI) in Japan. Parameter “κ” is computer according to Anderson and Hough (1984), while an automated signal energy-based procedure is developed to calculate the S-wave windows of each waveform, accounting for any errors. Site-specific restrictions on the upper frequency limit, f2, for the calculation of “κ” at the foundation level are imposed, based on the empirical transfer functions between foundation and free-field motions. Based on the above procedure, non-linear regression analyses are conducted to relate “κ”, as computed for free-field and foundation motions (κff, - κfnd), to magnitude Mw, source-to-site distance Repi and shear wave velocity VS30. Simulation of ground motions though the point-source stochastic method is accomplished, utilizing the regression expression to define “κ” and assess its effectiveness to predict the variation of intensity between free-field and foundation motions as a proxy for assessing soil-structure interaction effects. It is shown that the regression-based expressions, combined with stochastic simulations, consist a promising tool for correcting seismic motions recorded at a building foundation or basement levels and thus, for reliably predicting the corresponding intensity and characteristics of the actual “building-free” ground motions.

Effect of kinematic interaction on seismic response of offshore wind turbines on monopiles

AbstractInterest in renewable energy over the past decade has motivated a remarkable research on offshore wind energy. Due to the environmental loading conditions in the early developments of offshore wind farms, the focus of the research and engineering has been on aerodynamic and hydrodynamic subjects. However, earthquake has turned out to be a major design concern in seismic areas such as East Asia, Southern Europe, and United States. The topics include, among others, nonlinear response of foundations, soil liquefaction, and their impacts on foundation performance. An important topic in seismic soil‐structure interaction (SSI) analysis is the kinematic seismic response of foundations. This information is crucial for analyses based on the substructuring approach where both kinematic response and foundation impedances are key parameters. While considerable research has been spent on the latter topic, very little has been reported on the kinematic interaction. Large monopoles with low aspect ratios tend to rotate much more than regular piles in pile group foundations due to seismic waves. The rotation leads to additional load on the tower and the turbine. This article uses a rigorous numerical model for monopole‐soil interaction in layered soil and computes both rotational and horizontal responses at the pile head (seabed) as functions of frequency. A suite of generic homogeneous and heterogeneous soil profiles with shear moduli representative of clay (generally linear) and sand (generally parabolic) are considered in these analyses. Through representative analyses, both in frequency domain and time domain, it is illustrated how the kinematic interaction influences the earthquake loads imparted to an offshore wind turbine (OWT).

A Winkler-based model for inelastic response of soil–structure systems with embedded foundation considering kinematic and inertial interaction effects

In this paper, a parametric study is carried out on the ductility and displacement demands of structures with embedded foundation considering nonlinear soil–structure interaction (SSI). The soil–embedded foundation interaction is simulated using the beam on Winkler foundation concept. The bilinear behavior is also assumed for the equivalent single-degree-of-freedom (SDOF) structure. Effect of key parameters including fundamental period, level of inelasticity, soil flexibility, embedment ratio, and slenderness ratio on the seismic demands is examined. A family of soil–structure systems are analyzed subjected to a group of 33 ground motions recorded on alluvium deposits. Both sway and rocking components of foundation input motion are applied to the system. Results reveal that foundation embedment generally increases the ductility demand of the SDOF system. Moreover, the kinematic interaction (KI) effect on ductility demands is more prominent for structures with deep embedment ratios. As the aspect ratio increases, the role of rocking input motion on ductility and displacement demands becomes more noticeable. It is also concluded that the nonlinear SSI can increase the displacement demand of interacting systems as compared to the equivalent linear soil model. Based on the obtained results, a simplified expression is proposed to estimate the displacement ratio for soil–structure systems with embedded foundation considering KI effects.

Pile induced filtering of seismic ground motion in homogeneous soil

The foundation input motion (FIM) that a structure experiences during an earthquake, is known to be different from the free field ground motion due to soil structure interaction (SSI) effects. Kinematic interaction in a single pile can also introduce a rotational component to the FIM. Conventionally, soil structure interaction is performed by applying the free field ground motion to the structure ignoring the effects of kinematic interaction. Deep foundation elements such as piles are known to suppress certain frequencies of ground motion which in turn induces kinematic bending moments in them. In this study, kinematic soil pile interaction is simulated using 3D numerical models using a coupled finite element-boundary element method. Single pile, group pile and piled raft models in a homogeneous soil profile are analysed for vertically propagating shear waves. Three earthquake time histories with varying frequency content are considered in this study. Transfer functions are then plotted together to analyse the effects of pile induced filtering of ground motion. The ratio of response spectrum at the foundation level and free field ground, for the pile group considered, is found to closely follow the behaviour of a fixed headed single pile. It is found that embedment of the pile cap, as in the case of a piled raft can result in further filtering of ground motion.

A simple closed-form solution for kinematic responses of retaining wall incorporating the effects of shear stiffness of soils

The seismic behavior of retaining wall is governed by the kinematic soil-retaining wall interaction, which has been described by various methods such as elastic continuum model and Scott model. Due to their over-complexity in the expression or low accuracy, practical applications of such methods are limited. Thus, inherited the simplicity of the Scott model, a concise analytical solution, involving the effect of the shear stiffness of soils, based on the Pasternak model is presented in this technical note to evaluate the kinematic soil-retaining wall interaction. In addition, both the soil spring factor k and shear stiffness factor γ in the proposed model have been demarcated. As compared with the existing literature, a good prediction is achieved in the present model. Besides, the physical mechanisms underlying kinematic soil-wall interaction are detailed elaborated by carrying out a group of parametric studies regarding the effects of kinematic soil-retaining wall interaction. The results emphasize that the soil shear stiffness significantly influence the kinematic behaviors of retaining wall so that it is a critical element in the seismic design of retaining wall.

Measurement of vibrations generated by high speed railway traffic and evaluation according to international norms

High-speed trains are one of the most preferred ways of transportation. The fact that it is fast and safe, cost effective and not being effected by weather conditions provides many advantages for passengers but there are also many disadvantages for the buildings close to the train track and the people who reside in these buildings. In this study, a series of site tests were performed to obtain the acceleration recordings of the vibrations existing in free field of the soil and building foundation. The average shear wave velocity of soil was considered as 200m/s and the velocity of the high-speed train was taken as 250km/h. In this study, it is aimed to reveal the kinematic interaction between the free field motion and foundation vibration of the building while high-speed train passed. Furthermore, vibrations occurring under the current soil conditions of the study area were evaluated according to the key parameters defined in regulations of the Federal Transit Administration Report (FTA) and Human Exposure to Vibration in Buildings/Effects of Vibration on Structures (DIN 4150-2/3). It is seen that the compliance with the limit values specified in the regulations changes according to the purpose of use. The results showed that rigid foundations significantly modify the wave propagation and vibration level due to kinematic interaction effects.

Köprü Yapılarının Eş Zamanlı Sistem ve Girdi Tanılaması

Bu makale, deprem kayıtlarını kullanarak köprü yapılarının sistem tanılaması için yeni bir yöntem sunmaktadır. Köprüler, genellikle yapısal elemanlarının geniş mesafelere yayılmasından ötürü, diğer yapılara nispeten yer hareketlerinin uzamsal değişkenliğine daha hassastırlar. Bu nedenle, özellikle temelleri değişik zemin türlerine oturan uzun ve çok kolonlu köprülerin simülasyonlarında kullanılacak nitelikte yer hareketi kayıtlarının ölçümü karmaşık bir süreçtir. Bilhassa hem eylemsizlik hem de kinematik Zemin-Yapı Etkileşimi etkilerinin yaygın olduğu durumlarda, köprü Temel Girdi Hareketlerinin doğrudan ölçümü mümkün olmayabilir. Bu çalışmada, uzamsal olarak seyrek bir şekilde ölçülmüş sismik yapı davranış kayıtlarını kullanarak eş zamanlı sistem ve girdi tanılaması sağlayan yeni bir yöntem önerilmektedir. Önerilen metodun teyidi ve gerçek ölçekte problemlere uygulanabilirliğini doğrulamak adına, yöntem Golden Gate Köprüsü'ne uygulanmış ve elde edilen sonuçlar mevcut veriler ile karşılaştırılmıştır.

Frequency and intensity dependent dynamic responses of soil-steel pipe sheet pile (SPSP) foundation-superstructure system

Frequency and intensity dependent dynamic response behavior of soil-steel pipe sheet pile (SPSP) foundation and superstructure supported on it is studied in this work considering the soil-structure interactions (SSI) effect through experimental investigation by utilizing a physical scaled model of soil-SPSP foundation-superstructure (S-SPSP-S) system. The vertical shear resistance of SPSP foundation joint is assessed experimentally by using an element model of SPSP joint and the result satisfies the requirement laid in design code. The components of sub-structuring solution technique for dynamic response computation namely-the inertial interaction effect and the kinematic interaction effect are estimated through SPSP foundation head loading test and shake table experiment under 1-g conditions, respectively. Frequency and intensity dependent SPSP foundation head impedance functions (IFs) and effective foundation input motion (EFIM) are estimated from these experiments for inertial interaction and kinematic interaction, respectively. The total dynamic response of S-SPSP-S system is computed using the sub-structuring technique through superposition of the experimentally measured IFs and EFIM. The superimposed dynamic response is further compared with the experimental total dynamic response estimated from shaking table experiment with the model S-SPSP-S system. The comparison shows certain discrepancies particularly in resonance behavior of SPSP foundation system. The reason for such observed difference is the stiffness variation of SPSP foundation unit due to the nonlinear behavior of SPSP joint resulting from profound influence of superstructure mass. As a whole, the results and discussions presented in this paper will provide the reader a detail insight on the fundamental dynamic response behavior of S-SPSP-S system.

A quantitative assessment of the NCHRP 611 method for soil-structure interaction analysis of buried circular structures & a proposed improvement

The recent National Cooperative Highway Research Program (NCHRP) Report 611 titled “Seismic Analysis and Design of Retaining Walls, Buried Structures, Slopes, and Embankments” has been widely adopted as a guideline in the analysis design of buried/embedded structures due to its computational simplicity and broadly accepted accuracy for simple soil-structure configurations. However, the method is not without shortcomings. In particular, the NCHRP method is not sensitive to the inherently broadband frequency content of seismic input excitations, soil heterogeneities, and potential kinematic interaction effects. The present study seeks to quantitatively assess the brackets of the validity of the NCHRP 611 method—specifically, for soil-structure analyses of buried circular structures, and offers an improvement that is simple to implement. This is achieved through parametric studies using detailed nonlinear finite element simulations involving a broad range of ground motions, and soil and structural properties. The simulations are carried out with models that are parametric variations of a model that has been validated in a prior centrifuge testing program on embedded structures. A refined version of the NCHRP 611 method, which uses maximum shear strains obtained through one-dimensional site response analyses, is shown to produce fairly accurate results for nearly all of the different cases considered in the parametric studies. The basic version of the method, however, which is based on rough estimates of maximum shear strain and effective soil modulus, is observed to be highly inaccurate.

Seismic soil response of scaled geotechnical test model on small shaking table

This research comprises a series of shaking table tests and finite element analyses of scaled soil-foundation model to determine the dynamic interaction effects between the foundation and the underlying soil. The purpose of this work is to specify a realistic geometric scaling coefficient for test model to be used in a small-capacity shaking table. The scaling factor addressed in this study involves not only geometric similarity but also kinematic and dynamic similarity with the real system. The free-field soil response under different earthquake excitations for both real system and scaled test model was directly performed by using 2D finite element method under plane-strain conditions. The kinematic interaction of the shallow foundation slab on free-field motion was also examined. In this computational model, the behavior of the soil medium is idealized by linear elastic-perfectly plastic assumption with a yield surface according to Mohr-Coulomb failure criterion. Two different earthquake acceleration records as Chi-Chi (1999) and Loma Prieta (1989) have been carried out at the bedrock level of the soil-foundation system for this study. By comparing the results of the numerical analysis with data from the laboratory tests, the proposed geotechnical model can properly simulate the seismic response of the full-scale real system. It can be concluded that the kinematic interaction effects are negligible in the low frequencies. It should be noted that the local soil properties have considerably amplified the earthquake response of the free-field motions in comparison to the bedrock excitations.

Bridge Structure Dynamic Analysis under Vessel Impact Loading considering Soil‐Pile Interaction and Linear Soil Stiffness Approximation

The appropriate modeling of the soil‐pile interaction (SPI) is critical to get the reasonable dynamic responses of bridge structure under impact loading. Of various SPI modeling approaches, utilizing p-y and t-z curves is a common method to represent the nonlinear lateral resistance and skin friction of pile‐surrounding soil. This paper accomplished SPI modeling for the bridge pylon impact analysis with compression‐only nonlinear springs and linear dashpots. The kinematic interaction and pile group effect were incorporated into the SPI. A variety of pylon impact analyses were conducted under energy‐variation impact loads. The structure dynamic responses were compared and discussed considering the influences of pile group effect, soil damping, and axial t-z spring. An approximate approach was proposed to derive the linearized stiffness of soil for the purpose of engineering calculation. It was concluded from the extensive simulations that the impact load generated from higher initial energy induced more significant structural responses and larger soil inelastic deformation than smaller initial energy. The piles in the leading row possessed larger bending moments, whereas they exhibited smaller pile deformation than the responses of trailing row piles. Soil damping applied in SPI played positive roles on the reduction of structural responses. Replacing the t-z spring by fixing the degree‐of‐freedom (DOF) in the vertical direction was capable to yield satisfactory results of structural responses. The proposed linear soil stiffness was demonstrated to be applicable in the SPI modeling of structure impact analysis.