| Pathologies of defection in bridge's span centre and the crick in the box beam of long span continuous rigid bridge are found during the period of service, this problem troubles the the bridge engineering circles all the time till now. There're several reasons may cause the problem: the inaccurate estimation of the concrete's shrinkage and creep, the estimation of the prestress loss of prestressed long cables is not enough, the unfavorable strained condition caused by poor construction etc. Multi-aspect analyse of this problem is conducted to found out the major causes of this problem.Firstly, the cause of the long-span continous rigid bridge's pathologies are analysed from this aspect: the shrinkage and creep of concrete, loss of prestress, surcharge of mobile load and the factor of temperature.Secondly, the FEM model of a practice project of continous rigid bridge with a main span of 190 metres is set up by Midas/civil to analyse the sensitivity of defection in span centre of this aspect: loss of longitudinal prestress, the computation module of shrinkage and creep of concrete, the prestress loading age of concrete and surcharge of mobile load. A conclusion is drawed that the effect of the loss prestress especially longitudinal top slab prestress is most remarkable, the shrinkage and creep of concrete and the surcharge of mobile load also are very important cause. The FEM model of the total bridge is set up by Dr.bridge to analyse the influence of loss of longitudinal and vertical prestress cause the crick in the box beam. A conclusion is drawed that the effect of the loss of vertical prestress cause the crick in the box beam is remarkable.Finally, by synthesesing the research productions and summarizeing the experiences of the existing long-span continous rigid bridges, some improved design measures, computation measures, construction measures and correlative measures to control the pathologies are brought forward. |
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