DYNAMIC NONLINEAR-ANALYSIS OF PILE FOUNDATIONS USING FINITE-ELEMENT METHOD IN THE TIME-DOMAIN

A quasi-three-dimensional method of analysis is presented for the nonl inear dynamic analysis of single piles and pile groups. The analysis i s performed in the time domain using strain-dependent moduli and dampi ng, yielding at failure, and a no-tension cutoff. The analysis has bee n incorporated into the computer program PILE-3D and has been validate d using data from centrifuge tests on a single pile and a 2 x 2 pile g roup under simulated earthquake loading. Analyses of the centrifuge te sts demonstrated a significant reduction in soil moduli around the pil es during strong shaking and a corresponding reduction in pile stiffne sses. The time-dependent shear modulus distribution in soil around the pile is obtained as part of the output. This allows the time variatio n of dynamic impedances of pile foundations during shaking to be estab lished and allows a realistic assessment of the single-valued stiffnes ses and damping factors usually incorporated into commercial structura l analysis programs for the seismic analysis of pile-supported structu res. The analysis also demonstrates the importance of inertial interac tion between foundation and structure.