Experimental study on progressive collapse behaviour of intact and slightly earthquake-damaged exterior precast concrete joints, and finite element modelling of building performance

This study investigates progressive collapse behaviour of intact and slightly earthquake-damaged exterior precast concrete (PC) joints. To achieve this, an experimental programme was carried out on four exterior PC joints incorporated with headed bars and plastic hinge relocation method. These specimens consisted of two intact and two slightly earthquake-damaged joints which were tested under a penultimate column removal scenario. The test results demonstrated that these joints exhibited robust resistance during both flexural and catenary action (CA) stages. Although earthquake-damaged joints showed reduced stiffness and deformation capacity, their strength remained comparable to that of intact joints. However, column failure occurred due to excessive deformation combined with P-Δ effects. To gain deeper insights into the experimental findings, the moment-rotation behaviour of the tested joints from this study and companion studies on interior joints [1,2] was analysed and compared against UFC4–23–03 provisions [3], highlighting the influence of joint flexibility and collapse mechanisms. Specifically, the experimental moment-rotation curves aligned with UFC4–23–03 in terms of moment capacity but exhibited smaller elastic stiffness due to inherent joint flexibility. In addition, beam rotations surpassed UFC4–23–03 predictions because of the omission of CA while column rotations were limited by premature column failure. The experimental curves were subsequently integrated into a proposed 3D finite element model for progressive collapse analysis, which accounted for slab contributions. Numerical simulations underscored the significant role of tensile membrane action (TMA) in reducing middle joint displacement (MJD) and delaying column failure. In addition, the slightly earthquake-damaged structure exhibited a marginally smaller MJD compared to the intact structure, due to reduced ductility. These findings emphasised the necessity of proper reinforcement detailing to optimise TMA and the adoption of strong-column-weak-beam design strategies to enhance structural resilience. Additionally, robust column-to-column connections are recommended to prevent collapse under large deformations.