Study On Shear Strengthening Of PC Box Girder Bridge With Steel Plate

PC box girder bridge is the main type of highway bridge in China.However,with the development of China’s economy,traffic volume has increased year by year.Many PC box girder bridges have web oblique cracks,resulting in a significant reduction in the bearing capacity and applicability of the bridge.Therefore,PC box girder bridges should be strengthened.Steel-bonded reinforcement method is a commonly used bridge reinforcement method in China,which has the characteristics of simple construction,small influence on the original structure and strong economy.Based on this background,this paper adopts the method of combining theoretical derivation and numerical simulation to study the calculation theory of bonded steel reinforcement of PC box girder,so as to better promote the application of bonded steel reinforcement in engineering.The main work of this paper is as follows:Firstly,the failure mode of PC box girder reinforced by bonded steel is analyzed,and the structural measures that should be paid attention to in the reinforcement of PC box girder are given,so that the failure mode when the structure reaches the ultimate bearing capacity is shear compression failure.Then on the basis of this failure mode,the calculation theory of PC box girder strengthened with steel-bonded webs under normal service state and ultimate bearing capacity state is proposed.According to the calculation theory of PC box girder reinforced by bonded steel under normal service condition,this paper gives the calculation formula of stiffness and inclined crack width of PC box girder reinforced by bonded steel.Stiffness calculation theory is based on the assumption that stirrups and steel plates only bear shear force after web cracking.By establishing the equivalent stiffness calculation model based on the damage range of oblique cracks,and adopting the method of superposition of two-stage stress and deformation,the calculation formula of the actual stiffness of the members strengthened with bonded steel web is proposed.The calculation of inclined crack width According to the similarity of stirrup strain and inclined crack width variation,the calculation method of inclined crack width of PC box girder reinforced by bonded steel is given based on the calculation formula of inclined crack width proposed by Southeast University.At the same time,the finite element model beams（PBCX-1,PBCS-1）are taken as examples to verify the rationality of the above formula.Aiming at the shear bearing capacity of PC box girder strengthened with steel plate,the mechanical characteristics of prestressed reinforced concrete box girder strengthened with steel plate under different parameters were studied by changing the parameters of steel plate thickness,steel plate spacing,steel plate width and the damage degree of the structure before reinforcement.The results show that the reinforcement effect of steel plate is closely related to the damage degree of the beam and the amount of steel in the horizontal projection length of the oblique section.Then,according to the limit equilibrium state of the structure when it is damaged,the calculation formula of the shear bearing capacity of the inclined section of the structure after strengthening with bonded steel is proposed.Combined with the finite element simulation results and related literature,the correction coefficient Ψ_vb of the shear capacity of steel plate in the calculation formula was studied.