Investigation Of Anchoring Stresses On Prestressed CFRP Strengthening RC Box Beams

As a new type of composite material, CFRP that insteads of the traditional reinforce material is applied widely in reinforcement project. Thin-wall box girder structure have many advantages such as good mechanical, property material saving and so on, which have been widely applied to large span bridges and the construction engineering structure, moreover, the key that the CFRP reinforcement concrete structure succeeds or not lies the bonding properties fit and unfit quality between the CFRP and the concretes. Firstly, the thesis introduces the advantages of box section beam, explains the concept of the shear lag effect on a box girder and its development and current status. The present paper reviews the studies and application of strengthening concrete structures using CFRP, and strengthening concrete structures using prestressed CFRP and its features are reviewed in this paper. The paper comprehensively seeks the existent questions on the strengthening concrete box beam using prestressed CFRP. In this paper, the main research works are as follow:(1) Different kinds of parabolas are adopted to simulate axial displacement of box beam flange, considering vertical shear deformation and shear lag effect, differential equations of composite symmetrically laminated box beam under symmetrical bending have been deduced firstly, and difference functions and deflection functions in simple supported beam under a concentrated load at mid-span and two-equal-span continuous beam under concentrated load applied at mid-span respectively have been also deduced. Finally, connecting with the concrete example of composite thin walled box continuous beam, the theoretical results of this paper are compared with the result of the ANSYS finite element simulation and experiment results.(2) Firstly, using analytical method, a theoretical derivation is made for calculating the formulas of the interfacial shear stress along CFRP sheet-concrete bond surface after release of the prestressed CFRP sheet ends in concrete box beam strengthened by prestressed CFRP sheet, moreover, in order to guarantee the debonding between CFRP and concrete wouldn't take place, the paper deduces formulas for predicting the maximum achievable prestress level. Secondly, considering the shear lag effect on a box girder, the distribution formula of interfacial shear and normal stress under the action of the external load have been deduced. Finally, the paper has researched these two stages, using the superposition method. Formulas of anchoring stresses in reinforced concrete box beam with prestressed CFRP sheet were derived.(3) In this paper, finite element analysis program ANSYS is used for nonlinear analysis for reinforced concrete box beam with prestressed CFRP sheet, and the interfacial stress is estimated and the distributing is also obtained, and the result is contrasted with the theoretical results of this paper.(4) This paper presents the theoretical analyses on the transverse interfacial stress distribution of reinforced concrete box beam with prestressed CFRP sheet, and a new concept which is called the transverse interfacial stress coefficients is firstly proposed.