Research On The Key Technique Of Construction And Crack Control In Bottom Slab Of The Even-span Rigid Frame-continuous Girder Bridge

In recent years, so many girder bridges of rigid frame-continuous system won the competition of bridge design and were selected as the superior plans. The girder bridge of rigid frame-continuous system also named rigid frame-continuous girder bridge.This paper presents a case study on the Lunzhou Bridge, a long-span continuous box-girder bridge, also, a rigid frame-continuous girder bridge, located in Qingyuan, Guangdong, China. The research mainly concentrate on the closure procedure of main girder, the tension sequence of prestressing steel strands, the construction control and cure to bursting crack of bottom plate of the midspan closure section.Firstly, a finite element analyses for the concrete box-girder had been performed, which was based on the Lunzhou Bridge, and considering the influence of closure sequence to the deformation and the mechanics perform ance of the bridge, several different closure sequence simulation was carried out depending on the finite element model. Therefore, Optimal closure sequence were selected by comparing the linear and internal force.Secondly, By using finite element method with Midas Civil, the influence of the tension sequence of prestressing steel strands to the bridge have analyzed both in transition of continuing bridge system and the bridge alignment and internal forces. Also, optimal parameters of the finite element mo del were compared and selected, and the optimum tension sequence of prestressing steel strands has been achieved.Thirdly, Base on the grey system theory and the modern predictive control theory, the grey predictive construction control system of rigid frame-continuous girder bridge with considering the characteristic of large-span prestressed concrete rigid frame-continuous girder bridge have been established. And the newly predictive system has been applied in Lunzhou Bridge, Meanwhile, demonstrate the effectiveness of the system.Fourthly, In order to solve the problem of bursting crack in bottom plate of the midspan, the paper systematically elaborates the types, manifestations and reasons of concrete crack of bottom plate of the midspan closure section.Finally, A solid element model of midspan of Lunzhou Bridge has been established. Two different conditions has been considered, with and without the diaphragms, to analysis the bottom plate stress of box girder under the action of radial force, Therefore, analyzed the influence of bottom plate stress under the different parameters of structure design, and proposes measures for prevention-treatment on the crack reducing.