Research On Reinforcement Technology Of Inner Support Of Prestressed Concrete Box-Girder Bridge

At present,many prestressed concrete box-girder bridges have been built at domestic and overseas.In these completed bridges,due to the design,construction,vehicle loading,natural environment and other factors,resulting in different degrees of damage to some bridges.These damages will have an impact on the stiffness and strength of the bridge,and if not treated accordingly,the safety of these bridges will be a concern.Therefore,it is necessary to take reasonable reinforcing measures to improve the load-bearing capacity and serviceability of these bridges,which is now an urgent problem to be studied and solved.The specific work and conclusions of this thesis are as follows:(1)For the problem of mid-span deflection and beam cracking,the reinforcement method of installing additional steel trusses in the box-girder,referred to as the inner support reinforcement method,is proposed.The basic principle,basic structure,construction process and key construction techniques are explained in detail,and compared with other reinforcement methods.The results showed that: Inner support reinforcement method has a wide range of applications,simple,low cost,short construction period,no need to reinforce the pier and pier foundation,and is reinforced inside the box,which has little impact on the appearance of the original bridge.(2)Relying on the actual project,the disease of a prestressed concrete box-girder bridge is analyzed and the damage model is established using Midas/civil.Calculation and analysis of bridge forces without shrinkage creep,1-year shrinkage creep,and 10-year shrinkage creep.The results showed that: In the three conditions,the main beam bearing capacity and section stress and deflection satisfy the code requirements;however,the tensile stresses of the 11 super tensioned web plate prestressing tendons exceed the allowable stresses,and the bundles are close to the plastic working condition,with the risk of fatigue damage.And the long-term time-varying effect of concrete shrinkage creep has improved the main beam section stress and prestressing tendons tensile stress.(3)According to the damage simulation results,considering the most unfavorable case of 11 super tensioned web plate prestressing tendons are broken,the finite element model before strengthening is established,and computational analysis of the bridge before reinforcement.The results showed that: Except for the main beam diagonal section crack resistance and the remaining prestressing tendons tensile stress which do not satisfy the specification requirements,the others are satisfied.(4)Reinforcement of a prestressed concrete box-girder bridge by inner support reinforcement method,and establishment of the reinforced finite element model.Computational analysis of reinforced bridges and comparison with the calculation results before strengthening.The results showed that: After reinforcement,the main beam oblique section crack resistance and the remaining prestressing tendons stress all satisfy the specification requirements;the bearing capacity,positive section stress,oblique section main compressive stress and deflection of the main beam are effectively improved and are within the specification limits.The maximum combined stress of the selected materials for reinforcement satisfies the code requirements,and the strength of the steel truss node plate also satisfies the code requirements;and the inherent frequency of the bridge has increased.It shows that after the fracture of 11 super tensioned web plate prestressing tendons,the inner support reinforcement method can increase the stiffness of the bridge superstructure to a certain extent,improve the stress performance of the bridge structure,inhibit the continuous deflection and girder cracking in the span of the main girder,enhance the bearing capacity of the bridge structure itself,improve the service level of the bridge structure,and achieve the purpose of reinforcement design.