Research On Mechanical Properties Of Girder Segment During Precast And Installation In Composite Cable Stayed Bridge With Wide Width

The application of steel-concrete composite beam cable-stayed bridge is becoming more and more extensive.In order to shorten the construction period,the construction method of the beam is constantly improved.The new construction method uses the full-section-prefabricated beam segments,which will be transported to the site of the bridge for cantilever hoisting.The concrete wet joints will be poured in one time after the connection of multiple beam segments.Because the main beam does not form a composite structure at the joint of the two adjacent segments.Meanwhlie,lateral deformation and internal force exist in the wide girder during the construction process of cantilever hoisting.As a result,this method is easy to make the bridge deck crack.Based on this problem,the wide beam section form,full section prefabrication,two section installation and technical measures are studied in this paper.(1)On the basis of comparison of full section precast composite beam and steel box girder scheme,for the composite beam cable-stayed bridge with fast construction method of two sections and one casting wet joint,the stress and deformation of the main beam and the stress of the concrete bridge deck are calculated and analyzed by the finite element method.It is found that the finite element model of the bar can not simulate the measures taken in the construction process,and can not get the stress(principal stress and shear stress)of the bridge deck surface,as well as the force acting on the transverse direction and the frame effect.(2)The solid finite element model of composite beam cable-stayed bridge with prefabrication of main girder segments and cantilever erection method is studied.Based on the full-scale model launching test of group pin connections,a method is proposed to convert the mechanical properties of steel bridge deck interface with single nail equivalent area.And it is applied to the simulation of the finite element bond contact model.In addition,the computational efficiency and effectiveness of the bond interface method are verified by bonding with the interface,simulation analysing of the shear stud element and comparing with measured datas.(3)Two different construction methods,of concrete slab on wide composite girder are compared.One is cast-in-place method,the other is precasting and installation method.And the influence of shrinkage of cast-in-place concrete slab bridge on structure is analyzed.The technology of concrete slab on precast wide girder is studied.Futher on,the transverse prestress method of using self-gravity or cantilever loading to make steel girder bended is presented.The paper also presented a method of pushing at two sides of concrete slab to prestress in transverse.In addition,the mechanical mode and construction method are studied.At the same time,the three kinds of prestressing force,the effect of tansverse prestressing and the influence on structure are calculated and analyzed.(4)By simulating the structural stress and deformation of the main girder during the construction of Taizhou Bay Bridge,This paper analyzes the stress distribution of concrete bridge deck and the cause of local cracking during the period when the main girder is in the early stage of cantilever erection and proposes technical measures of cable pretension and self anchored temporary cable.Meanwhlie,based on the principle of stress of main girder structure and moment equilibrium for deformation control,we use polynomial and power function to fit respectively,calculate the reasonable pretension of each cable by cable pretension method and give construction parameters such as lifting force of temporary cable tower with different beam weight.Relying on application practice of engineering,this paper put forward the advance pretension technique which effectively solves the problem of concrete cracking of main girder bridge deck and section deformation and provides the basic data for the accurate matching installation of the main girder.(5)In order to reducing the main tensile stress of concrete slab during the construction process of installing full-section-precast girder,two technical measures were proposed.One is delaying the pouring time of partial wet joint.The other is applying temporary prestress.And the paper presents the specific construction scheme,technical parameters and precautions after finite element analysis.