Structural response and mitigating techniques for long-span cable-stayed bridges subjected to blast loading

Over the past two decades, blast loads have been recognised as one of the extreme loading events that must be considered in the design of important structures such as cable-stayed bridges. However, the design provisions for blast-resistant bridges are limited due to inadequate knowledge of the local and global dynamic response of the bridge under the blast loading scenarios. An explosion can result in partial collapse of the bridge and significant loss of life and property, as well as social and economic devastation. To design blast-resistant bridges, an understanding of the blast wave propagation and its effects on bridge structures are required. Recent advances in numerical methods and developments in high-performance computer facilities have enabled engineers to simulate complicated blast scenarios in a viable, efficient and cost-effective manner and subsequently to provide useful benchmark data for the safeguard design of critical infrastructure in the future. Accordingly, this study develops detailed finite element models of an entire cable-stayed bridge subjected to blast loading using the LS-DYNA FE code. Based on the best practice data obtained from the literature, the blast load estimation, material modelling and detailed numerical simulation are conducted. Different explosive sizes are considered and placed at different locations above the deck to determine the influence of the size and location of the blast loads on the global and local response of the bridge components. The results of the FE simulations are used to characterise the type and extent of damage to the pylon and deck, and also to investigate the potential cable-loss and progressive collapse scenarios due to blast load. Furthermore, the values of the so-called Demand to Capacity Ratio (DCR) and the maximum strain at different sections along the pylons are computed to establish a damage criterion. The blast performance of the pylon with a modified octagonal cross-section compared to conventional rectangular box sections, in addition to different protective methods such as application of sacrificial concrete blocks and CFRP sheets are investigated to identify the best mitigation strategies. The results of computer simulations also showed that the shorter cables were more vulnerable to direct rupture following the dramatic changes in their axial force due to explosion