Research On The Failure Mechanism And Safety Assessment Method For Urban Bridges Subjected To Blast Loads

Urban bridges, as the throat of land transportation, play an important role in bothnational economy and military transport. Their construction not only facilitates peopleto travel, but occupies an important position in the highly mobile modern life.However, with the increasingly severe struggle against terrorism, terrorist attacks oraccidental explosions are more and more frequent, so the problem of explosion failurefor urban bridges triggered by bomb explosion has attracted more and more attention.Explosion in the key parts may cause huge damage and traffic congestion, and evenmass casualties. It has a vital significance to research on the failure mechanism ofurban bridge subjected to blast loads, reasonable method can be used to determine thedamage condition of the bridge after the explosion in time, and assess the safetycondition of the bridge accurately and scientifically. Although the research onanti-blast for urban bridges has gained extensive attention of the existed researchersand engineers, safety assessment for urban bridges subjected to blast loads has notreceived its due attention. The research achievements are extremely limited, many ofwhich cannot be directly applied to engineering practices. Therefore, it is necessaryand proper to put forward a practical and convenient safety assessment method forurban bridges subjected to blast loads. Based on the existing scientific achievements,the failure mechanism and safety assessment method for urban bridges subjected toblast loads are been studied systematically. The main contents are as following:1. The basic phenomena of explosion and theory of blast shock wave are beenstudied systematically.2. A numerical simulation method for the failure and damage mechanism ofurban bridges under blast loads is elaborated.3. According to the damage characteristics of the whole structure or localcomponents under blast loads as well as the current situation of urban bridges, anumerical simulation based safety assessment method for urban bridges subjected toblast loads is proposed. First, a calculation formula for safety index basing on yieldstress and the maximum accumulated stress of each control section is proposed.Second, the dynamic response of urban bridge is analyzed, and the maximumaccumulated stress of each control section after the explosion is obtained. Then, thesafety index of the bridge is calculated. In the end, basing on the safety index, thesafety condition of the whole bridge is assessed. 4. Basing on a large-span steel truss arch bridge in a certain city center, the finiteelement models are established. Then, by using the nonlinear finite element softwareANSYS/LS-DYNA, the dynamic response and the safety assessment of this bridge isobtained. In the end, by comparing the calculations of different working conditions,the influence rules of the safety condition under different dynamite quantities,carriageways and vertical positions of the bridge are ascertained.