Nonlinear analysis of pile groups subjected to combined lateral and torsional loading

An empirical approach has been developed to analyze the nonlinear response of a pile group with arbitrarily distributed piles subjected to combined lateral and torsional loading. In this approach, the concept of instantaneous twist center is applied to analyze the displacement relationship of pile heads and establish the static equilibrium equations of the pile cap. The horizontal interaction among the individual piles is considered through the generalized p-multiplier. The coupling effect of lateral resistance on the torsional resistance of each pile is quantified using an empirical factor beta; the lateral and torsional nonlinear responses of individual piles are modeled by p-y and tau-theta curves, respectively. The proposed approach not only captures the most significant aspect of the group effect and coupling effect in a pile group subjected to combined lateral and torsional loading, but also automatically updates p-multipliers of individual piles based on pile cap displacements. The proposed approach was verified using results of model tests on pile groups subjected to lateral loading, torsional loading, and combined lateral and torsional loading, separately. In general, the pile cap response and the transfer of applied loads in the pile groups agree well with the test results.