Progressive collapse resistance of precast frame structure subjected to loss of a middle column

To study the progressive collapse resistance of precast frame structures subjected to the loss of a middle column, five one-third scaled two-bay beam-column substructures were constructed. The load resisting mechanism and failure mode of the substructures were investigated using the pushdown loading approach. The test results demonstrate that the connection type (i.e., top-seat angles connection, unbonded post-tensioning connection, and hybrid connection) has great effects on the load-resisting mechanism. As the longitudinal reinforcements are discontinuous across the beam-column joints, flexural action commonly mobilized in cast-in-place concrete frames is not developed in the specimens with unbonded post-tensioned connections. When the specimens are installed with top-seat angles at the beam-column interfaces, considerable flexural action could be developed. The failure modes and load-resisting mechanisms of the specimens with unbonded post-tensioned connections are quite different from those of conventional cast-in-place RC frames. For precast concrete frames with unbonded post-tensioned connections, the catenary action of post-tensioned strands is the main source of the load resistance. High-fidelity finite element models were developed using the software LS-DYNA. After validation, parametric studies were carried out. The numerical results show that bonded post-tensioned strands could increase the initial stiffness of the specimen slightly in the small deformation stage. However, bonded post-tensioned strands may result in earlier fracture of the strands, less deformation capacity and lower load capacity in the large deformation stage. © 2022, Editorial Office of Journal of Building Structures. All right reserved.