Study Of Design Methods For Strengthening RC Beam Bridges By Bonding Steel Box

Steel box strengthening method is a new reinforcement method based on the theory of steel-concrete composite beams, combining the advantages of the reinforcement of enlarging section and bonding steel plates. This method bolting and affixing the H-shaped steel plates to the bottom of the beam, then welded a steel plate to the lower edge of the H-shaped steel plates to make the lower part become a closed steel box. The steel box and concrete beam can work together with the function of anchor bolts and adhesives, thus could improve the stiffness and load capacity of the beam. Steel box strengthening method is an effective reinforcement method, it just need short construction period and simple construction technology and can greatly improve the bearing capacity of the beam. So it has a broad prospect of application in practical engineering.The beam reinforced by steel box is a steel box-concrete composite beam. This paper derived the stress formula of the reinforced beam based on the theory of elasticity, and analyzed the bend and shear capability of the reinforced beams based on the theory of plasticity and the principle of steel-concrete composite beam. Establish the finite element model of Rectanglar RC beams, analysis the reinforcement effect of steel box strengthening method by comparing the FEM’s stress characteristics before and after reinforcement. Through the finite element analysis of 12 RC beams, analysis the influence of steel box height and side plate height to reinforced concrete beams. According to the characteristics of steel box strengthening method,analysis the influence factors on the capacity of the steel box reinforced beam, including re-force effects, desquamation, slip effect, the ageing of structural adhesives and bolt strength etc. Based on the practical application of steel box strengthening method on LanZhou DongGang overpass bridge, analysis the disease of this type of bridge, evaluate the reinforcement effect by comparing the load test result. This strengthening method could applied to similar bridge.Practice has proved that, steel box strengthening method can improve the beam’s bend and shear capacity and reduce the mid span deflection. This reinforcement method can be applied to the similar bridge reinforcement project.