Blast-Response Characteristics of a Double-Leaf, Double-Arched, Bidirectionally Supported Protective Door

Urban underground spaces are increasingly developing toward large-scale and multifunctional configurations, imposing higher requirements on the large span and ultimate load-bearing capacity of protective doors for critical infrastructure. To address the low load-bearing efficiency and susceptibility to local instability of conventional large protective doors, this study proposes a novel double-leaf, double-arched, bidirectionally supported protective door incorporating a rear grillage and horizontal coupling beams, based on a spatially coordinated load-bearing system. First, the dynamic response of a rib-stiffened double-leaf arched protective door, designated Type I, was investigated using the finite element code LS-DYNA. To address its closely spaced higher-order modal frequencies and insufficient stiffness, a preliminary optimization was conducted by adding a rear grillage, resulting in the Type II configuration. The stress concentration and localized connection damage caused by stiffness incompatibility in Type II were then examined, and a final optimized design incorporating horizontal coupling beams was proposed (Type III). The results indicate that the coordinated restraint provided by the rear grillage and horizontal coupling beams effectively mitigates the reduction in the fundamental frequency and the local stress concentrations observed in the Type II structure. The fundamental frequency of the Type III structure is 7.9% higher than that of the Type I structure. Under severe blast loading, the Type III structure exhibits a substantially improved load-transfer path. Compared with the Type I and Type II structures, respectively, its maximum displacement is reduced by 7.30% and 14.09%, and its peak equivalent plastic strain by 19.15% and 22.84%. Consequently, the Type III structure exhibits improved global deformation compatibility and effectively suppresses local instability. This study elucidates the spatially coordinated load-bearing mechanism of the double-leaf, double-arched, bidirectionally supported protective door under severe dynamic loading and represents a promising structural candidate for the innovative design and optimization of large protective doors for critical underground infrastructure.