Study On Crack Control Of Long-span Prestressed Concrete Continuous Rigid Frame Bridge During Construction Period

At present, the concrete crack of long-span prestressed concrete continuous rigid frame bridge is a generally existing problem, and the existence of crack would threatens the safety and durability of bridge structure seriously. The survey results of practical project cracks prove that most cracks of prestressed concrete continuous rigid frame bridge have generated during the bridge construction. However, the studies on how to effective control cracks of long-span prestressed concrete continuous rigid frame bridge during construction period are rare. Therefore, some farther and systematic research is needed to do. Based on practical project, this paper studies crack control of long-span prestressed concrete continuous rigid frame bridge during construction period by experiment test, field test and finite element emulation analysis. The main contents are summarized as follows:(1)Reasonable preparation technology of high performance concrete for box girder of long-span prestressed concrete continuous rigid frame bridge was studied by rationally selecting concrete components, designing and optimizing concrete mix proportion. On the basic of rationally selecting concrete components, the influence rules of binding material on concrete performance were studied. Meanwhile, the proportional ratio test, the cracking resistance test of concrete on early-age and the autogenous shrinkage test on early-age were carried out. The results show that: during the preparation process of high strength and high performance concrete, properties of raw materials should been investigated and optimized for guaranteeing the quality of raw materials; Slag can reduce hydration heat effectively and improve the cracking resistance performance of concrete on early-age; The amount of slag should be between 15% and 30%.(2)The concrete hydration heat in the No:0 block of box girder of a long-span PC continuous rigid frame bridge was observed continuously, and based on the field test results and the numerical simulation calculation by FEA, the temperature stress development law of the bottom plate, web and diaphragm were analyzed. Meanwhile,the influence of the construction scheme on the hydration heat temperature stress of the No:0 block box girder was discussed and the influence of the form removal time on temperature difference was researched. The results show that: the temperature reached the peak at 30 h after pouring concrete; The excessive temperature differencewould cause the excessive temperature stress and the temperature cracks. Besides, the tensile stress field would be formed near the interface between the top and the bottom concrete in the No:0 block of box girder by distinct-layer casting, the maximum would reach 1.68 MPa; The research results also showed that the form removal time should not be less than 4 days to prevent temperature cracks.(3)Based on field test results, the losses of vertical prestress and lateral prestress have been investigated in detail and compared with the calculated value by using current specifications. The results show that: the losses due to anchorage deformation, retraction of tendons and joint compression of vertical prestress is lower than the calculated value, constituting 35.3% to 52.8% of the total loss. The calculation results of vertical prestress losses, based on the current specifications, all agree well with the measured results except the loss due to shrinkage and creep of concrete.And, the calculation results of lateral prestress losses, based on the current specifications, all agree well with the measured results.