Response Spectrum Method for Kinematic Soil-Pile Interaction Analysis

Abstract

The detailed seismic responses of pile-soil systems are usually evaluated by a three-dimensional finite-element model which requires a lot of computational resources. In the actual structural design for these models, a computationally efficient method with a reasonable accuracy is preferred from the viewpoint of cost and time. As for the seismic response of a pile-soil system, a kinematic effect due to the forced displacement of the surface ground is considered to be important, especially in soft ground, together with the inertial effect due to the inertial forces from superstructures. In this paper, a new response spectrum method in terms of complex modal quantities is developed for the evaluation of the maximum kinematic seismic response of the pile-soil model to the ground motion defined at the engineering bedrock surface as an acceleration response spectrum. The ratio of the pile-head moment due to the kinematic effect to that due to the inertial effect will be discussed in detail.

Unified analysis of kinematic and inertial earthquake pile responses via the single-input response spectrum method

“…In the evaluation of the bending moment in a pile, both the effect of the forced displacement of a free-field ground (action 1) and the effect of the inertial force from a superstructure (action 2) as shown in Fig.1 have to be taken into account in an appropriate manner (for example [1][2][3][4][5][6][7][8][9][10][11]). However these two effects have different characteristics and it seems difficult to include these in a simple way keeping a reasonable accuracy.…”

“…This is because the phenomena in the geotechnical engineering are mostly described by the wave propagation theories and the treatment of those phenomena as vibration problems has seldom been conducted so far except models with viscous or transmitting boundaries [10]. While the wave propagation theories can deal with an infinite medium and hysteretic damping, a complex treatment is necessary in the vibration theories.…”

“…In order to investigate the accuracy of the present method using the dynamic Winklertype spring, a single pile of diameter=1.0(m) and length=20(m) in a homogeneous semiinfinite ground of shear wave velocity=100(m/s) and damping ratio=0.05 has been analyzed in [10]. It has been demonstrated through the comparison with the thin-layer method [25][26][27] that the present method using the dynamic Winkler-type spring has a reasonable accuracy.…”

“…However, a numerical stability problem may arise in this overall model due to the much difference in numerical order between the free-field ground and the pile-soil system. The method developed in [10] is applied to the problem for investigating the superposition rule of the kinematic and inertial responses of the structure-pile-soil system.…”

“…However the proposal of more comprehensive analysis methods is desired and this can be done efficiently and effectively by combining the response spectrum method proposed in [10] with a new method for evaluating the inertial response. A simple analysis method of the inertial response using the same response spectrum method is proposed here by introducing the constraint on the free-field ground (the fixed condition of the free-field ground) and an amplification factor for the total inertial response (Section 4).…”