Performance-based Seismic Fragility Analysis Of Aizhai Bridge

Many large suspension bridges have been built in our country, marked by thecompletion of the first large modern suspension bridge Bay Bridge of Shantou.Aizhai Bridge, which has been supplied to use in2012, developed our country’sstandard of suspension-construction to an international degree. However, theWenchuan serious earthquake made us be conscious of the transportation lines’importance again. Large span suspension bridges are general key projects intransportation lines. When greatly build the large suspension bridges, the fragilityanalysis is absolutely in need.Upon views above, the thesis used Midas civil to establish a3-D model of AizhaiBridge and did some fragility research of large span suspension bridge. Main contentsand conclusions are as follow:(1) The key sections of bridge towers were defined and different damage indexes werecalculated by P-M-θ analysis, using section curve calculated by material strain asbroken index of the bridge tower.(2) The3-D model of Aizhai Bridge which used fiber element to analog bridge towerwas built by using the bridge analysis software—Midas civil so that the incrementaldynamic analysis of Aizhai Bridge was run. Via the analysis the thesis studied thedamage-broken rules of bridge tower by gained the distribution of envelop-Moment.Damage assessment of each key sections of bridge towers were also made by u singdefined damage indexes. In conclusion, the fragile sections were distributed in thebottom of lower part, the bottom and top of upper part of Jishou-bridge tower andbottom of lower part of Cha-bridge tower.(3) Influence of field characteristics was discussed in the thesis. The research showedthat seismic effects in field type Ⅲ were far higher than that in field type Ⅰ.Seismic effects in field type Ⅱ and Ⅳ were between that in Ⅰ and Ⅲ but moreclosed to Ⅲ.(4)18seismic waves were selected from the database of Pacific earthquakeengineering research center and the selected seismic waves were setted by10strengthdegrees. Via incremental dynamic analysis the thesis got a series of fragility curves ofthe key sections of bridge towers. And then comparision of exceeding probability in asame damage state of different key sections was analysed and the fagility curves in terms of the whole bridge was also built. The research showed that the bottom sectionof Ji-tower was the most fragile part of the bridge. Slight damage exceedingprobabilitied of Cha-tower sections were comparatively big but the medium damageexceeding probabilities were all very small. The damage plastic hinges were morelikely emerging in Ji-tower.