Effect of pile-cap connection on behavior of torsionally loaded pile groups

To evaluate the responses of fixed and pinned pile groups under torsion, a method is presented to analyze the nonlinear behavior of free-standing pile groups with rigid pile caps. The method is capable of simulating the nonlinear soil response in the near field using p-y and tau-theta curves, the far-field interactions through Mindlin's and Randolph's elastic solutions, and the coupling effect of lateral resistance on torsional resistance of the individual piles using an empirical factor. Based on comparisons of the solutions for fixed- and pinned-head, 1x2, 2x2, and 3x3 pile groups subjected to torsion, it was found that pile-cap connection significantly influences the torsional capacity of pile groups and the assignment of applied torques in the pile groups. In this study, the applied torques for the pinned-head pile groups are only 44\%similar to 64\% of those for the corresponding fixed-head pile groups at a twist angle of 2 degrees. Such a difference is mainly due to the change of the lateral resistances of individual piles in the groups