Effects of non-linear soil-structure interaction on dynamic characteristics of structures supported on piles

Mahmoud N. Hussien, Mourad Karray, Tetsuo Tobita, Susumu Iai

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Earth Walls and Foundations

ABSTRACT: non-linear soil-structure interaction on dynamic characteristics of structures supported on piles Mahmoud N. Hussien & Mourad Karray Department of Civil Engineering, Sherbrooke University (QC), Canada Tetsuo Tobita & Susumu Iai Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan ABSTRACT A series of linear and non-linear seismic response analyses of soil-pile-structure systems is performed using two-dimensional finite elements, emphasizing on the vibrational characteristics of the coupled system. The interaction between the pile and the surrounding soil in three-dimensional type was idealized in the two-dimensional analysis using soil-pile interaction springs with hysteretic non-linear load displacement relationships. Soil models were idealized by multiple shear mechanism of hyperbolic type. The results indicate that soil-structure interaction effects were observed for coupled systems that comprise of stiff superstructures founded on flexible and/or long piles; leading to significant reductions in the effective natural frequency of the system, fSSI. The nonlinearity of the ground induces larger reduction in frequency ratio indicating the strong need to revisit the current interaction methodologies based on linear elastic SSI. RÉSUMÉ Une série danalyses de réponse sismique linéaire et non-linéaire de systèmes sol-pieu-structure est réalisée en utilisant des éléments finis en deux dimensions, et ce, en mettant l'accent sur les caractéristiques de vibration du système couplé. L'interaction entre le pieu et le sol environnant dans les trois dimensions est idéalisé dans l'analyse en deux dimensions en utilisant des ressorts d'interaction sol-pieu avec des relations charge-déplacement hystérétique non-linéaire. Les sols ont été idéalisés par un mécanisme de cisaillement multiple du type hyperbolique. Les résultats indiquent que les effets interaction sol-structure ont été observés pour les systèmes couplés qui constituent des superstructures rigides reposant sur des pieux flexibles et / ou longues; conduisant à des réductions significatives de la fréquence naturelle efficace du système, FSSI. La non-linéarité du sol induit une plus grande réduction du rapport de fréquence indiquant la forte nécessité de revoir les méthodes d'interaction actuels basés sur les analyses élastique linéaire SSI. 1 INTRODUCTION Under seismic excitation, a structure found on a compliant ground could respond differently compared to a fixed-base situation. Indeed, in flexible supported case, mutual interaction between structure and adjacent soil takes place inducing modifications in the dynamic response. Also, the seismic response of structures supported on piles differs from that on surface foundations due to the increased stiffness of the pile-soil system as compared to soil only, and due to the scattering of seismic waves off the piles (Kim and Stewart, 2003). The design of a structure-pile-soil system for earthquake loads must take into account the effects of the foundation on the earthquake ground motion, the effect of foundation compliance on the loads experienced by the structure (kinematic effect), and the effects of the inertial loads imposed by the structure on the foundation (Inertial effect). In the past, free-field accelerations or velocities or displacements were considered as input motion for the seismic design of structures without considering the effects of kinematic interaction. However, depending on the soil profile, pile properties and dimension, and the excitation frequency, pile response may be greater than or less than the free-field response (Hussien, 2011). A comprehensive reviews on the subject have been presented, among others, by Novak (1991), Meymand (1998), and Gazetas and Mylonakis (1998). Up to date, no tool or chart is available to estimate the vibrational characteristics of structures supported by piles embedded in deformable soil taking into account pile properties and dimensions, soil profile, soil nonlinearity, the relative soil-pile stiffness, and the relative stiffness of the soil and the structure (Hussien, 2011). In this paper, linear and non-linear seismic response of single degree of freedom (SDOF) structures supported on piles embedded in dry sand is parametrically studied, emphasizing on the vibrational characteristics of the soil-structure system. These series of parameter study were performed to act as a base to develop simple charts for predicting linear and non-linear response of SDOF structures supported on piles. To this end, fully two-dimensional (2D) finite elements (FE) models of coupled soil-pile-structure systems are analyzed in the frequency domain under harmonic excitations introduced at the base of the soil profile. The interaction between the pile and the surrounding soil in three-dimensional (3D) type was idealized in the 2D analysis using soil-pile interaction springs with hysteretic non-linear load displacement relationships. Soil models were idealized by multiple shear mechanism of hyperbolic type, FLIP (Iai et al. 1992). This paper cover particular issues that can be summarized as follows: (a) examining soil-pile-structure interaction in terms of the modified dynamic properties of the coupled system, (b) investigating the combined effect of kinematic and inertial interaction on the motion of the

RÉSUMÉ: ts of non-linear soil-structure interaction on dynamic characteristics of structures supported on piles Mahmoud N. Hussien & Mourad Karray Department of Civil Engineering, Sherbrooke University (QC), Canada Tetsuo Tobita & Susumu Iai Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan ABSTRACT A series of linear and non-linear seismic response analyses of soil-pile-structure systems is performed using two-dimensional finite elements, emphasizing on the vibrational characteristics of the coupled system. The interaction between the pile and the surrounding soil in three-dimensional type was idealized in the two-dimensional analysis using soil-pile interaction springs with hysteretic non-linear load displacement relationships. Soil models were idealized by multiple shear mechanism of hyperbolic type. The results indicate that soil-structure interaction effects were observed for coupled systems that comprise of stiff superstructures founded on flexible and/or long piles; leading to significant reductions in the effective natural frequency of the system, fSSI. The nonlinearity of the ground induces larger reduction in frequency ratio indicating the strong need to revisit the current interaction methodologies based on linear elastic SSI. RÉSUMÉ Une série d

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Cite this article:
Mahmoud N. Hussien; Mourad Karray; Tetsuo Tobita; Susumu Iai (2014) Effects of non-linear soil-structure interaction on dynamic characteristics of structures supported on piles in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper289,author = Mahmoud N. Hussien; Mourad Karray; Tetsuo Tobita; Susumu Iai,title = Effects of non-linear soil-structure interaction on dynamic characteristics of structures supported on piles ,year = 2014}