Analysis of the synergetic effects of blast wave and fragment on concrete bridges Haiqing Zhu1,*, Xiedong Zhang1, Ying Li1 1. School of Transportation, Wuhan University of Technology, Wuhan 430070, China * Corresponding author: zhq7751@163.com Abstract: The complicated loading caused by explosions is not well understood, so the effect is often simplified when calculated. In order to increase the bridge protective level, a penetrating study of the mechanism of the synergetic effect of blast wave and fragment is necessary. Numerical simulation is used to analyse the dynamic response characteristics and the damage performances of the reinforced concrete bridge. Three conditions were designed to research the synergetic effect of the blast wave and fragment on the bridge. The research indicates that the synergetic effect is larger than the arithmetic sum of the effect of blast wave and fragment separately, which should be taken into account in the protection of bridge. Keywords: Blast wave, Fragment, Synergetic effect, Dynamic response 1. Introduction Several decades has witnessed that destroying bridges is the best efficient way to restrict the enemy for cutting off the transportation line and blocking supply in the local conflict. Moreover in many developing areas, infrastructure construction is blooming, blast is the fastest way to demolish the old un-qualified bridges. When bomb or missile exploding, blast wave and fragment are produced and both them impacted on the bridges. In recent years, either blast destroy bridges or fragment penetrate concrete is studied very well. But the complicated combined loading caused by synergetic blast wave and fragment is not well known. However design a blast test to research the synergetic effect is insecure and expensive. Numerical analysis using AUTODYN is the appropriate mean to study the mechanism before material test. 2. Loading characteristics 2.1 Blast wave characteristics When explosions occur, the energy released at a lighting speed, which produce gas mixture with high temperature (3.5×103—4×103 ) and high pressure ℃ (1×104—3×104MPa). Since the air initial pressure and density is low, explosive product diffused at a high speed will compress the air nearby, increasing the air pressure, density and temperature drastically, which will develop into blast wave. The blast wave spread rapidly, during the energy spread and deplete, the speed of the blast wave will decay rapidly. When the volume of the explosive product expands big enough, the pressure in it will drop to the original level 0P of the air nearby. However the product volume will keep expanding to a maximum because of the inertia effect. Then the negative pressure area will occur because the average pressure of the product is lower than the original pressure 0P , and the air nearby will compress the product conversely, which will increase the product pressure. For the air, the first expansion—compression impulse is worthy of study. Classical blast wave spread in air is shown as figure 1.
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