Analysis On Concrete Creep Effects During The Cantilever Construction Of Continuous Rigid Frame Bridges

Creep is an inherent property of concrete. Because of the complexity and important influence for structures, the study on concrete creep can trace back to 100 years ago but it is still a hot research topic now.During the construction of continue rigid frame bridges, creep is a technical problem that can not be avoided. Creep can lead to errors of the stress monitoring during the construction of continue rigid frame bridges and make the line of the bridge hard to control. Based on this background, the paper did some research in the creep to seek ways for calculating the its effect during the cantilever construction of continue rigid frame bridges. The main work is as follow:(1) The paper introduced the influence factors, creep models, and the calculation methods of creep. The sensitivity of each parameter of the creep coefficient formula in our country's norm- JTGD62-2004 "Highway of reinforced concrete and prestressed concrete bridge and culvert design specification" was analyzed and drew a conclusion that the influences of the average relative humidity and the strength of concrete for creep were much more significant than the other parameters'.(2) From the mechanical point of view, the deformation caused by the same load in reinforced concrete structure and the same size concrete structure is different, because of the additional internal force between reinforcing bars and concrete. Based on the force equilibrium and deformation coordination, the paper deduced the method of creep calculation considering the influence of reinforcing bars. The method was proved to be correct by an example.(3) During the cantilever construction of continue rigid frame bridges, the structures are statically determinate, so the creep doesn't lead to the increase of stress. In order to analyze the force status of the bridge structures correctly, the creep should be calculated and deducted from the stain tested by strain sensor. Based on creep theory and principle of superposition, the paper deduced the stress correction formula for the construction of continue rigid frame bridges. The formula was used in the stress monitoring for the Hun Shuihe Bridge, and was proved to be effective. (4) Based on the creep calculation method called "By Age-Adjusted Effective Modulus Method" and principle of superposition, the paper deduced a formula of calculating deflection caused by creep. The deflection of Hun Shuihe Bridge caused by creep during its construction was calculated using this formula and the construction pre-camber was adjusted to guarantee the lines of the bridge.