The Application Research Of Stress-Free State Accelerate Iteration Method In Construction Control Of PC Cable-stayed Bridge

Since the 21 st century,China's transportation industry has made great progress.As the key node and hub project of the transportation infrastructure interconnection,bridge has been paid more and more attention.Cable-stayed bridge is widely used as a typical type of long-span bridge.There are various construction methods of cable-stayed bridge.At present,the most commonly used construction method is the balanced cantilever construction in stages.In order to obtain the reasonable stress of the completed bridge,the internal force analysis in the construction stage is needed.Compared with the traditional incremental analysis method based on staged incremental accumulation,the unstressed state method is favored in determining the staged construction state of the bridge without the influence of process adjustment and many external factors.In this paper,based on the existing research results,the accelerated iteration formula of the unstressed state method considering the effect of concrete shrinkage and creep on the unstressed state quantity of the structure is summarized,and its application scope and suggestions are pointed out.Finally,taking a single tower cable-stayed bridge with two cable planes as an example,the comparison and verification of the two methods are carried out.The specific research contents of this paper are as follows:(1)this paper first introduces the current mainstream calculation methods of the reasonable completion and construction state of cable-stayed bridges,and expounds the advantages,disadvantages and uses of various calculation methods;discusses the stress-free length and curvature in detail,and explains the calculation steps and process of the stress-free state method combined with the characteristics of the stress-free state method.On this basis,the action law of concrete shrinkage and creep effect is expounded,and the action mechanism of shrinkage and creep effect in the process of staged construction of concrete cable-stayed bridge is obtained,which changes the amount of unstressed state of structure,and then leads to the inconsistency between the internal force,displacement of tower beam and the force of stay cable and the reasonable target state of completed bridge caused by staged construction.(2)referring to the relevant literature,further analyzing and summarizing the mechanism and law of the effect of shrinkage and creep on the unstressed state quantity of the structure,and summarizing the basic principle and formula derivation process of the unstressed state acceleration iteration method.Taking a simplified cable-stayed bridge with two pylons as an example,the initial checking calculation of the stress-free state acceleration iteration method considering the effect of concrete shrinkage and creep is carried out,which verifies the feasibility and reliability of the method.(3)taking a single tower and double cable plane cable-stayed bridge with a large span and a large number of cables as an example,the traditional unstressed state method and the unstressed state accelerated iteration method are compared and verified.First,the traditional unstressed state method is used to analyze the cable-stayed bridge,and then the unstressed state accelerated iteration method is used to analyze.The results of the two methods are compared,and the cable force and the unstressed cable length difference in each construction stage are compared.The comparison of the calculation results shows that the reasonable completion state of the cable-stayed bridge can be effectively determined by using the stress-free state acceleration iteration formula on the premise of considering the shrinkage and creep effect of concrete.Compared with the traditional stress-free state method,the calculation efficiency and accuracy are improved.