عنوان مقاله [English]
Piles are often placed closely in a group to serve as the foundation of specific structure, such as offshore platforms, bridge structures and tall buildings. Pile groups should be capable of withstanding significant lateral loads induced by seismic excitations, winds, waves, and current loads. The main objective of this research is to investigate the effect of the stiffness of the pile cap on the behavior of piles embedded in sand under dynamic loads, by means of the 3D finite difference method. Previous research shows that pile cap stiffness, connection type of pile-cap and soil-pile-structure interaction play important roles in the behavior of laterally loaded pile groups. Beam elements are used in this study to connect each of the piles, and these connections are rigid. Further, due to he nfluence f he uperstructure on the behavior of pile foundations, this effect is modeled in the analyses. To account for the soil stiffness acting on the pile shaft, normal and shear springs are accommodated in the interface of the soil and pile elements. To evaluate the data for the parameters of the interface elements, a 2D finite difference analysis has been performed to calculate the required parameters of the interface elements at various depths. To model sand and structural members, Mohr-Coulomb and elastic models are employed, respectively. For dynamic analyses, attention has been paid to quiet boundaries, free fields, and wave propagation in the soil medium. Four different arrangements have been considered for pile cap. Results of analyses show that a increase or decrease in cap stiffness does not necessarily change extreme induced forces (i.e., maximum shear force, bending moment and lateral displacement) along the piles in the group. However, for a given mass of the system, there is a range of stiffness for the pile group that has maximum effect on induced internal forces and lateral displacements. For a flexible pile cap, the induced bending moments and shear forces along the individual piles depend on the location of the piles in the group.