Handling the exceptions: robustness assessment of a complex structural system

摘要

The robustness of a structure, intended as its ability not to suffer disproportionate damages as a result of a limited initial failure, is an intrinsic requirement, inherent to the structural system organization. A robust design cannot therefore be limited to design the structure just for additional accidental load cases, but should take into account the response of the structure to different damage conditions. Complex structural systems like the long suspended bridge considered in this paper, in case some failures involving the suspension system occur, can be inclined to the propagation of the damage, due to the high continuity of the long central span. Some specific investigations aimed to robustness assessment have therefore to be carried out on the structure: following a bottom-up approach the critical event modeling can be neglected and an initial failure has to be a-priori assumed on the structure, in order to evaluate if and how much the overall response of the structure is influenced from a local failure. The investigations presented in this paper start from assuming an abrupt rupture of some hanger ropes of the suspension system and investigate the response of the system to different damage levels and locations. This kind of investigations require quite complex nonlinear dynamic analyses to be performed, in order to account for the dynamic amplification caused from such abrupt initial failures and for the plastic reserves of the materials that the system can exploit during the collapse.