Study On External Prestressing Reinforcement Method For Long-span PC Continuous Beam Bridge

Prestressed concrete continuous girder bridge is the main bridge type in China's traffic network.The number of this type of bridges is increasing year by year.Some long-span PC continuous girder bridges were found to have deflection and cracking after several years of operation,which affected the normal using function of the bridges seriously.It is necessary to restore its using function by reinforcement.External prestress reinforcement is an effective method suitable for reinforcing this type of bridges.In this paper,the analysis of present condition and external prestress reinforcement method of a PC continuous beam bridge with a span of 62m+100m+62m are studied.Firstly,the causes of the diseases are analyzed based on the results of the bridge diseases and load test,which provides the research direction for assessing the bridge condition.Then,quantitative analysis of the causes of web disease and bottom plate disease is carried out by using the finite element software to establish the integral model of the bridge,focusing on analyzing the impact of the insufficient effective prestress and heavy vehicles on the structure.Assessing the bridge condition and carrying out the structure check based on the results of the bridge diseases and load test.After that,the causes of cracks of box girder roof are analyzed and the box girder condition is judged by establishing local finite element mode.Focusing on analyzing the impact of the temperature gradient and heavy vehicles on the stress of the top plate of the box girder.Then,external prestress reinforcement scheme is designed based on the bridge condition,focusing on the study of the external prestressing design and the anchor block design.Finally,the structure check is carried out on the reinforced bridge.The study of the example bridge shows that the combined effect of insufficient effective prestress and overload vehicles is the main reason for the deflection and cracking of the girder,the combined effect of vertical temperature gradient and overload vehicles is the main reason for the longitudinal cracks in top plate of the box girder;It is recommended that the crack resistance of the reconstructed bridge deck should be checked strictly when reducing the thickness of the bridge deck pavement to improve the structure stress;In this paper,the formula of estimating external cable area is modified and the efficiency of designing reinforcement scheme is improved;At the same time,the method of designing corner anchor block is proposed,by specializing the independent anchor block and the corner anchor block,and referring to the code for highway bridges,which is convenient for bridge designers to design corner anchor block;The check result of the reinforced bridge shows that the external prestress reinforcement scheme can effectively improve the crack resistance and restore the normal using function of the bridge;Finally,it is commended to strengthen the management of the reinforced bridge,and it is forbidden for overloaded vehicles to cross the bridge.