Research And Application Of Concrete-replacing Method At Bridge Pier Cap

The sticking strengthening method,concrete-replacing method and enlarged section method are common methods to consolidate reinforced concrete bridges.Among them,the concrete-replacing method is to chisel off the defective or lowintensity concrete in the original structure and then cast the concrete with higher strength than the original concrete,which is ensuring that the new-old concrete well combines to bear the stress together.Currently,the concrete-replacing method is studied by many researchers and many important results are obtained.However,it is still necessary to further analyze and optimize concrete-replacing method.Meanwhile,it is also important to accurately obtain the working stress of the concrete structure at the replaced location and design a reasonable stress relief plan,which is to avoid the phenomenon of stress lag,so that the new-old concrete structure can combine well and work together.Based on concrete-replacing method,this paper studied the reinforcement of the defective concrete at the 3# pier cap of Kangqiao.It used MIDAS CIVIL and ANSYS for calculation and analysis,reasonably considered the influence of temperature variation on the internal force of the concrete structure,and proposed the bridge deck loading method to release the stress of original concrete.It aimed to provide a relatively reasonable and effective reference for similar actual projects in the future.According to the research of this paper,the conclusions are as follows:(1)The comparison between the additional internal force generated by the concrete structure under temperature variation and the internal force generated by the dead load can be seen that the internal force generated by the concrete at the bridge pier cap under the temperature variation cannot be ignored.And because the finite element model simplifies the actual structural boundary constraints,the strain of the concrete structure measured under temperature variation is about 20% different from the strain calculated by the finite element modeling.Therefore,in the process of concrete-replacing method,when the finite element model simplifies the boundary constraints of the actual structure,the calculated stress and actual value of the concrete structure may differ greatly,and it’s better to compare with them.If there exists a great difference between them,it could use the ratio of them to calculate the corresponding correction factor,to make the result nearly reach to actual situation.(2)Considering that the rate of reduction of additional stress on the new-old concrete joint surface is more and more gentle as the loading age of the newly poured concrete increases,the effect of the loading age of newly poured concrete on concretereplacing method is studied.Taking the finite element analysis of a concrete column for example and taking into account the construction period and economic benefits are to reasonably select the loading age of the newly poured concrete,in order to appropriately reduce the additional stress on the new-old concrete joint surface and the effect of creep on concrete-replacing method.(3)The relationship between shrinkage creep of concrete and the reinforcement assembly ratio is discussed.The reinforcement assembly ratio of the column is taken as the only variable,and it simultaneously uses the deformation coordination condition of the reinforcement and concrete,that is,the deformation of reinforcement is equal to the shrinkage creep value of concrete,so as to discuss the shrinkage creep value of concrete under different reinforcement assembly ratios.(4)The working stress of the concrete structure is measured by the drilling method,and compares with the working stress calculated by the finite element software.The measured values of the working stress are in good agreement with the calculated values,thus it verifies that the working stress obtained by the numerical analysis is relatively reliable,which provides a reliable basis for stress relief of old concrete.Meanwhile,this paper proposes a method,the bridge deck loading,to release the stress of the old concrete at the bridge pier cap.(5)The reinforcement effect of concrete-replacing method is analyzed.Firstly,the comprehensive analysis of the force state before and after bridge reinforcement is carried out by MIDAS,and the local calculation of the 3# bridge pier cap by ANSYS;Secondly,the reinforced concrete structure is tested for concrete strength,concrete density and the quality of the new-old concrete joint surface.Finally,it performs the bridge static load test as well as the comparative analysis of the experimental results and calculation values.