| The majority of modern cable-stayed bridge is using cantilever construction method,because of cantilever construction without support system and it is not restricted by rivers and bridges under traffic.The structure of large span cable-stayed bridge constructed by cantilever construction is a geometry variable system before the closure.There will exist unbalanced moment in cantilever construction,that is the reason tower-beam temporary fixation construction setting on the pier top for.We always use the beam element calculation method what base on plane section assumption and neglects transverse distribution to check the safety of tower-beam temporary fixation construction using in large span cable-stayed bridge.Through calculating the bearing reaction force of tower-beam temporary fixation and average distribution to the structure,we check the structure safety.In practical engineering,due to the difference between the main beam and the temporary structure,the temporary consolidation of the beam is not absolutely consistent with the plane section assumption.Without considering into account the lateral distribution,the bearing reaction will also lead to the temporary fixation construction of the partial structure of the safety reserve insufficient.In view of this problem,to Fengdu Yangtze River Bridge as the engineering background,this paper analyzes the constructing bridge tower and beam temporary fixation construction force characteristics in space,and researches on the principle of force.Starting from the principle of mechanics of the structure to make an optimization design.The specific research contents are as follows:1)safety checking of Chongqing Fengdu bridge temporary fixation construction example.Firstly,using the finite element software MIDAS / civil,the beam element model was established to analyse the North Tower full bridge construction process,and points out that no cable construction stage in the whole process is the worst stage for the tower-beam temporary fixation construction.However after considering spatial effect of solid element calculation,pointed out the shortcoming in beam element calculation method,and found the mechanical problems that the temporary fixation construction concrete buttress of the cross bridge to the lateral bearing support counter force rapid growth,the medial bearing counter force growth slowly or even no growth.2)proposed the steel box girder cable stayed bridge tower and beam temporary fixation construction bearing force distribution mainly received the cross section of the steel box girder frame structure on the hypothesis,and using MIDAS / civil establish respectively beam element and solid element model to verify it.3)proposed the temporary fixation construction optimization method and integrated using it as follow: more than a hypothesis based,by changing bearing location,to determine the minimum pre tension shall set in temporary fixation construction of prestressed of steel beam,these design change means improve bearing force.Based on the phenomenon that the inner bearing is less stressed,an improved construction technology to balance bearing force is put forward to make the inner bearing to support more weight of a part of the beam body and the pre tension.From the root cause that the upper part of a large imbalance moment,proposed the classification lifting construction method to reduce to bearing force.4)researched and analyzed of the horizontal force generated by the longitudinal temporary limit restriction in special position.Proposed the position change,set the external prestressing constraint and the bearing support pad replacement three optimization schemes.Finally,the calculation verifies that the best way in example isbearing support pad replacement.This study can expose many past never care bearing by the large local stress and spatial effect of additional internal force and increase the design personnel on temporary fixation construction degree of attention.It offers a reference for the future design and construction personnel. |
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