Reinforcement Method For Prestressed Continuous Girder Bridge Cracking During Construction

Based on the engineering example of Datong River Bridge,this paper studies and analyzes the actual situation of cracking and deflection of the mid-span main beam caused by the instability and deformation of the full support after the main beam roof is cast-in-place with full support.The simulation model is established by the finite element software MIDAS/CIVIL.Combined with the existing theory,the influence of cracking and deflection of the mid-span of the prestressed concrete continuous beam bridge on the completion of the bridge and the effective reinforcement method are studied.Research shows that:(1)The stress and deflection results of the main girder during the reasonable completion of the bridge are simulated and analyzed as a reference,and the stress and deflection results after the completion of the bridge are co MPared and analyzed when the main girder deflections are 20 mm,40mm and 60 mm respectively near the midspan of the main girder during the full support construction.The maximum compressive stress of the normal section of the main beam after deflection 20 mm and 40 mm is-10.1MPa and-10.3MPa respectively,and the minimum compressive stress is-0.7MPa and-0.2MPa respectively.The stress and deflection meet the requirements of the specification,and have little effect on the bridge,but the safety reserve of the mid-span section of the main beam is significantly reduced.When the deflection is60 mm,the maximum compressive stress of the main beam is-10.6MPa and the maximum tensile stress is 2.7MPa after the completion of the bridge.The main beam has tensile stress,which does not meet the requirements of the specification and needs reinforcement.(2)After strengthening the lower edge of the mid-span main beam by using the pasting steel plate method,the deflection value of the main beam increases slightly to meet the specification requirements;The maximum compressive stress of the main beam is-11.0MPa,the maximum tensile stress is 1.6MPa,which does not meet the requirements of the specification,and the reinforcement effect is not significant.(3)After strengthening the lower edge of the mid-span girder by using the section-increasing method,the deflection value of the girder increases slightly,but meets the specification requirements;The maximum compressive stress and tensile stress of the normal section of the main beam are-12.3MPa and 0.7MPa,which do not meet the requirements of the specification.At the same time,the stress concentration occurs on the original main beam at both ends of the reinforced section.This reinforcement method has a good effect on improving the stress of the main beam.(4)After the reinforcement of the full-span box girder by external prestressing tendon method,the deflection of the main girder has a good improvement,the maximum compressive stress of the main girder is-9.9MPa,the minimum compressive stress is-1.3MPa,and there is no tensile stress.Reinforcement on the main beam deflection and stress improvement effect is good,meet the specification requirements,reinforcement effect is good.(5)By coMParing and analyzing the stress and deflection of the main girder after reinforcement by the three reinforcement methods,it is concluded that the external prestressed reinforcement method is more suitable for Datong River Bridge and the reinforcement effect is better.