Analysis Of The Precast RPC Column Reducing Long-time Mid-span Deflection Of Large PC Rigid Frame Bridge

Long-term deflection is a prominent problem for the large rigid frame bridge, forming a vicious circle with cracking, which pose a great threat to the operation safety and durability of the structure. Creep and shrinkage of concrete under compression has been considered as the most important factor of l ong-term deflection. In view of the fact that RPC(reactive powder concrete) has high strength,almost no shrinkage,small creep coefficient after heat curing,a method of adding precast RPC column into the bottom plate of the negative moment region and mid-span roof of the middle span to form RPC-NC(Normal Concrete) composite section is proposed to solve above problem.Internal force redistribution and its effect to reduce later deformation of RPC-NC composite section column has been researched by experiment, theoretical and finite element analysis. The mechanical capability of shear bond is also studied, thus acquiring the reasonable proportion of area of RPC. Based on above research, design scheme of prefabricated RPC column used in actual bridge is put forward, and then the influence of precast RPC column on the whole bridge stress and mid-span deflection is analysed by contrast of finite element. Main conclusion is as following:(1) Because of internal force redistribution due to the great difference of RPC and C50 of composite section column, compression stress of C50 will eventually decrease, as well as of the composite section column later deformation and the nominal creep coefficient; Coefficient of RPC can calculated as 15% of NC under the same circumstance; Shear bond will be safe and effective when its area accounts for 4% of the composite section; It is effective and reasonable when RPC ’s area accounts for 40% of the composite section.(2) Compared to the NC rigid frame bridge, long-term deflection of the rigid frame bridge which add precast RPC column has decreased 54.5%, which significantly improve the bridge disease of long-term deflection; Compression stress of NC at mid-span bottom and zero block roof has increased, while compression stress of NC at mid-span roof and zero block bottom has decreased, which make compression stress distribution of the bridge more even; Prestress loss caused by creep and shrinkage of concrete of bottom plate later prestressed tendon in the middle span and roof plate prestressed tendon in the negative moment region don’t have obvious change.(3) The main reason that long-term deflection of the rigid frame bridge significantly decrease after adding the precast RPC col umn is: partial composite section has form in the bottom plate of the negative moment region and mid-span roof of the middle span to form RPC-NC, which lead to the decrease of NC ’s compression stress and nominal creep strain, thus reducing the rotation of the negative moment region and vertical displacement at mid-span.(4) Through Parameter analysis, precast RPC column is advised to be arranged at the bottom plate of block 0~8, roof plate of block 24~26 and mid-span closure segment.In conclusion, joining the appropriate proportion of precast RPC column reduce the long-term deflection by about 50%, significant ly improving long term deflection problem the rigid frame bridge, thus having a certain reference value in practice.