Abstract
Recently, it was found out by authors' numerical analysis that superior performance of CFT piers under unidirectional alternate loading is primarily attributed to a unique behavior that restrains the progress of local buckling deformations in steel tube. Herein, the validity of this behavior under more realistic seismic loads is examined experimentally by carrying out bi-directional shaking table test as well as bi-directional cyclic loading test. From the responses of strains and deformations measured in the cyclic loading test, it was observed that the axial compressive force acting on steel tube is mostly transmitted to the in-filled concrete by diaphragm as soon as local buckling deformation occurs in steel tube. This phenomenon slows down a progress of buckling deformations. Furthermore, under the cyclic loading subsequent to the occurrence of the local buckling, opening and closing of a major horizontal crack along with dilation in the in-filled concrete results in tensile stresses in a locally buckled steel tube. This tensile stresses remove the local buckling bulges by stretching them. From the shaking table test, a remarkable self-centering behavior was observed in CFT piers, although their hysteretic curves are not originoriented. The numerical analysis showed that the unique behavior of CFT piers to remove local buckling deformations occurred during the shaking table test. Therefore, this behavior might have some effect on the self-centering behavior of CFT piers.
