Load-carrying mechanisms of 3D post-tensioned precast concrete sub-structure under internal column removal scenario

To shed light on structural response of a post-tensioned precast concrete (PTPC) sub-structure under an internal column removal scenario, a large three-dimensional (3D) beam-slab assembly was tested under twenty-four-point quasi-static loading. The specimen was a two-by-two bay floor with primary beams, secondary beams and slabs. The primary and secondary beams were designed with precast concrete using wet-connection joints in which post-tensioned (PT) tendons were used in the primary beams only. Besides, precast half planks were employed for the slab panels. A proper restraint system along the four sides was designed to facilitate mobilization of all load-carrying mechanisms in the sub-structure. The test results, including the load-displacement curve, joint rotation and deflection profile, crack pattern and failure mode, and load redistribution, are presented and discussed in detail. The test results revealed the distinctive roles of different load-carrying mechanisms in the sub-structure at different stages. In addition, a simplified analytical method was developed to predict the flexural and tensile capacities of the 3D sub-structure. The method could predict the respective contributions of individual members such as the primary beams, secondary beams and slabs, thereby allowing structural engineers to control the behaviour of the 3D sub-structure at different stages.