The Determined Method’s Research Of Optimal Maintenance Timing For Long-span PC Box Girder Bridge’s Downwarping

Large span prestressed concrete box girder bridge,with its structural rigidity,beautiful and simple bridge style, integrity and continuity of good, smooth ridecomfort, fewer joints and a series of advantages such as easy maintenance, bridgeconstruction，has been widely used in our country, which is one of the main bridgeamong the range of40m~200m span. But a variety of diseases and problems alsoappeared in the operational process of long span PC box girder bridge, mainlyreflected in the lower box girder cracking and cross-scratch. These two diseases arevery common, and so far there is no good solution. So for the bridge maintenancedepartments it is essential to made the reasonable choice before determining themaintenance and reinforcement strategy, which made a big different to the outcomesof the Large span prestressed concrete box girder bridge and deteminded therationality of the Reinforcement strategy.In this thesis, relying on the North River Bridge project, from the two mostcommon diseases of the PC box girder bridges span: the lower cross beam deflectionand cracking, analysis the status and influence resulted from the two most mainlydiseases, and select one box girder lower deflection as the research object, through theestablishment of the finite element analysis models and the reliability calculationmethod, derived based on the mid-span deflection under the span PC box girderbridge structure degradation failure probability prediction model, and then throughthe target to determine the reliability of a large cross-PC box girder bridge optimalmaintenance reinforcement timing, the main research contents are as follows:1. Establish the long span PC box girder bridge span in the lower deflection limit stateequation, according to the method of calculation to retain the reliability of PC BoxGirder Bridge span across the middle and lower torsion reliability index. Explorevarious design parameters on the performance of large span box girder bridge ofservice rules, raise the methods of calculation in the lower torsion based on cross spanPC box girder bridge reliable indicator, through the service period span PC box girderbridge span deflection the reliability index variation for analysis, obtain the PC BoxGirder Bridge span deflection performance degradation under the law and reliabilitydegradation prediction model.2. According to the literature, explore the mechanism of degradation of the structure and its corresponding analysis model, the establishment of long span PC box girderbridges span the period under flexible service capacity and reliability indexcorresponding degradation curves were investigated.3. According to the span PC box girder bridge maintenance and management neededto determine the structure of the target reliability to establish the based on thereliability index of the probability distribution model, and thus proposed span PC boxgirder bridge reinforcement timing probability optimal maintenance determinationmethod which can be applied to practical engineering.