Analysis Of Concrete Stress Of Continuous Rigid Frame Girder Cantilever Casting In Construction Period

At present,concrete bridge construction in China due to the price reason,most of the methods used to cast concrete in the field,due to ensure the workability of the cast-in-place concrete,and fresh concrete in the transportation,pumping process to maintain a good state,which prompted The composition of modern concrete has undergone major changes,leading to significant changes in the performance of modern concrete,especially early performance,compared to ordinary concrete.The early shrinkage of concrete changes greatly,which directly leads to an increase in the probability of cracks in the bridge during the construction period.For the cantilever cast concrete box girder,there are also the special features of its construction.The early maintenance of concrete box girder during the construction process is mainly concentrated on the top surface of the box girder roof and the areas within the box where the personnel can reach.The outer surface of the girder web and the bottom plate bottom relatively affected by the environment are due to the lack of construction channels.Very few maintenance or even maintenance,which makes the outside of the box beam is very easy to produce shrinkage cracks.In the construction of Chongqing's Gan Shui bridge,the compound maintenance method of “steel formwork bottom with mold attachment + artificial maintenance +water spray fog curing” has been adopted.The bridge bottom floor and cracks in the box girder were found in the late bridge inspection.The situation is better than the same type of bridge that did not use this method.However,this method lacks further theoretical arguments.Therefore,the stress analysis of the continuous rigid-frame bridge cantilever pouring construction is carried out to determine the rationality of the compound curing method,thus forming a complete set of conservation engineering methods,so as to promote the use.This paper analyzes the impact of early shrinkage of modern concrete on cracking of concrete by collecting existing literature data,and then analyzes the effect of template paste on the relative humidity distribution of concrete,and proposes finite element simulation of concrete humidity field with template paste and mold curing.The calculation method was applied to simulate the distribution of humidity field and the initial stress state in the mid-span section of the construction process of Long Ju Bridge,and the rationality of the compound curingmethod was theoretically demonstrated.Specifically completed the following work:(1)Finite element software does not directly solve the function of the humidity field,but with reference to the similarity of the temperature field and the humidity field,combined with the solution of the temperature field and the solution of the thermal stress,the finite element software can simulate the changes of the humidity field and the internal stress of the concrete.(2)Through the test of the test block,the effect of concrete curing method on early shrinkage and water dispersion of surface concrete under two different environmental humidity conditions was investigated.(3)The finite element analysis of the test block is performed and compared with the test value to ensure the accuracy of the simulation of the humidity field of the concrete and the rationality of the simulation of the simulation.(4)Based on the Long Ju Bridge Project of Wanli Expressway,the initial stress state of the adjacent two box beams under natural conservation and compound curing state was analyzed to further demonstrate the rationality of using the compound curing method for Long Ju Bridge.