Compressive Behavior Of RC Bridge Piers Strengthened Underwater By Using BFRP Shells

With the increase of traffic volume and time,the underwater structures of bridges are prone to disease,and these diseases will negatively affect the safety and serviceability of bridges.Once the underwater bridge structure loses its original safety and durability,it will have serious consequences and cause huge loss.But,due to using cofferdam to carry on the drainage construction,the traditional underwater bridge structure reinforcement method has limitations,such as long duration,large-scale construction influence,high cost and inflexible method.In order to meet the requirements of reinforcement and repair of damaged bridges and make up for the deficiency of traditional reinforcement techniques,the technology of rapid undrained reinforcement of underwater bridge piers with BFRP shell is proposed in this paper.Through the experimental research,numerical simulation,theoretical analysis and pilot project,the feasibility and effect of the reinforcement method were analyzed.The main work and achievements are as follows:(1)Taking four parameters into consideration,i.e.underwater non-dispersive concrete mix ratio,concrete filling amount,pouring environment and reinforcement ratio of the strengthened column,a total of 12 axial compression specimens and eccentric compression specimens were designed and manufactured,and the corresponding tests were carried out.The results show that the bearing capacity,ductility and lateral deformation capacity of strengthened columns are greatly improved.The load bearing capacity increases by at least 112%.The reinforcement of axial compression column and small eccentric column is more effective than that of large eccentric column.The filled-in concrete with expansive agent can fully exert the circumferential restraint function of BFRP shell,but the restraint effect of BFRP shell on core concrete decreases when filled-in concrete has too much reinforcement amount.(2)To further investigate the factors affecting the reinforcement effect of BFRP shell,based on the experiment results,41 axial compression models and bias models were established by ABAQUS finite element software.The effects of non-dispersive underwater concrete amount and strength,BFRP shell strength,size effect on the reinforcement effect of BFRP shell were analyzed.Some reinforcement design suggestions were proposed.Under the premise of satisfying the reinforcement demand,the best concrete area ratio before and after reinforcement is about 1.5-2.The filled-in concrete strength grade should be higher than that of the strengthened concrete structure by 1 strength level.(3)Based on the experiment results and finite element analysis,the calculation formulas of the axial compressive and the small eccentric compressive bearing capacity of BFRP shell confined concrete cylinder are proposed.(4)On the basis of the pilot study of Xizi Xiang Bridge,the construction process and quality-control essentials are summarized,which lays a foundation for the popularization of the rapid reinforcement technology of underwater structure without drainage of BFRP shell in the future.