Study On Bearing Capacity Evaluation Method Of Old Prestressed Concrete Bridge

Prestressing tendon is the key stressed member in prestressed concrete bridge, and it is directly related to the safety, applicability and durability of the structure. The engineering practice shows that structural failure caused by the invalidation of prestressing tendon is irremediable. Therefore, it is an important and urgent issue to have study on bearing capacity evaluation method of old prestressed concrete bridge.In this paper, by classifying general influencing factors, the hierarchy model is built up by means of AHP, then the weight of each influencing factor can be obtained firstly. Because the prestressing tendon and the concrete in the compressive zone can not lose efficacy at the same time, while section and reinforcement are determined already, so the strain coordination analysis method in American norm (ACI) is adopted to judge the failure mode of the structure. The weight of the prestressing tendon will be improved when it gets pulled cut. Secondly, the ratings of influencing factors are subsequently gained by qualitative or quantitative method. Finally, the reduction coefficient for old prestressed concrete bridge is figured out by means of fuzzy comprehensive evaluation, then we can evaluate the practical bearing capacity of old prestressed concrete bridges using bearing capacity reduction coefficient, structure section reduction coefficient and reinforced section reduction coefficient.Taking the demolition of the main lane bridge of Xiawan Bridge as background, the bearing capacity of the auxiliary lane bridge is evaluated using the suggested evaluation method in this paper. It is proved to be feasible by the gantry cranes test detection.For the prestressing tendon of bonded post tensioning, residual prestress exists after relaxation due to the cohesive action of the duct grouting, so if it is taken into consideration in old bridge demolition, the bearing capacity of the structure can be enhanced, the demolition scheme can be optimized and the cost due to bearing capacity insufficient also can be reduced. In this paper, taking the demolition of the main lane bridge of Xiawan Bridge as background, we discussed the relaxation for post-tensioned prestressing tendon using the transfer length theory of pre-tensioned prestressing tendon for reference.