Vertical Bending Response Of Suspension Bridge Under Air Explosion Loading

The long-span suspension bridge is a main style of large bridges with span over 1000m nowadays, and plays an extremely important role in the means of transportation. Aim at the threat of explosion attack, the vertical bending response of suspension bridge under air explosion is studied theoretically and numerically, the transient response of the structure is investigated especially. The main work and results are as follow:(1) Based on the published results, a theoretical distributed formula for the transient impulse load caused by the air explosion above the bridge axes is proposed and validated. The results show that the impulse distributed formula which can be easily employed, is available in the vertical bending response of suspension bridge and the response's error is less than 10 percent comparing with the AT Blast software's result.(2) A simple planar model for computing the vertical bending response of a long-span suspension bridge is established and it's first 6 vibration modes are obtained by the linear deflection theory, and the analytical solutions of the vertical bending response caused by explosion above bridge's mid-span is derived by the mode superposition method. The results show that the bridge's frequency of free vibration and the dynamic deflection are preferably consistent with the numerical simulation's result, with the error less than 5.5% and 8.5% respectively, while the inner force of the analytical solutions is much smaller than the numerical result, not considering the transient response of the suspension bridge. Therefore, the vertical bending response of the suspension bridge under instantaneous impulse should adopt the method of numerical simulation.(3) The process and mechanism of the suspension bridge's vertical bending response cased by symmetrical and unsymmetrical transient impulse loads, are studied with the numerical simulation of the ANSYS software. The results show that, the suspension bridge's vertical bending response under explosion impulse can be divided into the unstable phase and the stable phase. The maximum of the bridge's inner forces occurs in the unstable phase. In the unstable phase, the inner forces of the bridge's components change greatly, with the interaction of the joint components being intense, while in the unstable phase, the inner forces fluctuate around their constant inner force, with the interaction weakened.(4) The inner forces of the bridge's components are investigated fully and numerically with the factors such as the ammunition's horizontal position, weight and explosion height between deck and bomb. The results are as follow: The bomb's horizontal position has an obvious influence on the inner forces of the beam and suspender, while it has a little influence on the main cable's inner force. The bomb's weight and the explosion height have an obvious influence on the inner forces of the beam and suspender, with the inner forces of the beam largely changing when a bomb explodes at the end of bridge especially, while they have a little influence on the main cable's inner force. The most harmful loading position of beam is at the end of the bridge, while the suspender's is at the middle of the bridge.