Failure mode discrimination and theoretical prediction method for unequal span bonded prestressed concrete substructures against progressive collapse

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Unequal-span prestressed concrete (USPC) structures have unequal spans on the left and right sides and are configured with prestressed steel strands on both spans. However, research on the progressive collapse resistance of these structures is lacking. The strength of the asymmetry of the USPC structure varies depending on the span ratio and reinforcement configuration, resulting in two distinct failure modes in progressive collapse. A parametric analysis was conducted using finite element software to determine how the resistance to progressive collapse and failure modes of USPC structures under middle column failure are affected by variables such as the span ratio, reinforcement configuration, and proportion of prestressing. Accordingly, a discrimination criterion for determining the failure modes of USPC structures was proposed. A theoretical approach for predicting the ultimate displacement and resistance of the progressive collapse of USPC structures was presented for different failure modes. This theoretical approach proposes an innovative stiffness combination and tension path method to establish displacement coordination and force equilibrium conditions, respectively. The theoretical prediction method was deemed valid after comparing it with finite element simulation results.