Study On Construction Control Of Concrete Cable Stayed Bridge In Stress Free State Method

The construction and erection of presrtressed concrete cable-stayed bridge usually have a long span while time for concrete curing and mould removal of bridge's main beam is limited because of construction process.The construction span may be longer if cantilever construction method is applied to construct main beam,on which the shrinkage and creep effect has a greater impact.This paper focuses on how stress-free status method resolves unclosed phenomenon,caused by the shrinkage and creep effect,in construction control of cable-stayed bridge.Structurally,the paper includes following four main parts:The first section gives a general introduction about the history and current progress of cable-stayed bridge at the very first;secondly,the purpose,necessity and approaches of construction control of cable-stayed bridge;thirdly,the development of stress-free status method;then,a sum-up of difficulties arose when stress-free status method is implemented in construction control of cable-stayed bridge;and finally,the problem to be resolved in the paper.The second section concentrates on the impact of the shrinkage and creep effect on stress-free state variables in construction control of cable-stayed bridge.The calculation method of stress-free length of cable and stress-free curvature of beam and tower is presented.Through checking stress-free state variables under the shrinkage and creep effect in theoretical means,it proves that stress-free status linear is changed indirectly and then unclosed phenomenon unfolds.In the last part of this section,an example is exemplified to vindicate that the shrinkage and creep effect indeed works on stress-free state variables and stress-free status linear,which lead to unclosed phenomenon.In the third section,the causes and solutions of two types of unclosed phenomenon,namely unclosed phenonmenon factors in calculation and unclosed phenomenon factors in status,are introduced.With regard to unclosed phenomenon factors in status,the focal point is placed on the impact of forced and unforced closure methods on internal force of cable-stayed bridge and the comparison of advantages and disadvantages between these two methods.With regard to unclosed phenomenon factors in calculation,this part centers upon comparison between backward-forward iteration method and stress-free status method,two construction control means.In combination of practical examples,the principles and procedures to settle down unclosed phenomenon of these two construction control methods depending on iteration are summed up.In the last part of this section,through practical calculation,the better method to solve unclosed phenomenon is singled according to the standard of feasibility and applicability.The forth section introduces prestressed concrete cable-stayed bridge across South Taihu Lake in Zhejiang province,a project controlled by stress-free status method.This instance validates that one way to analyze closure is to take the iteration of shrinkage and creep effect into consideration.Besides,the application of forward-iteration method in construction control is also explored in this section:the confirmation of construction cable force in every stage,the increase amount of anchor head,the extraction of structural linear camber,the support on construction control.Ultimately,there is a sensitivity analysis of vital parameters in construction control,including main beam linear,main beam stress,displacement of the head of bridge tower and cable stress.From what have concluded from the analysis,some structural responses should be given attention if relevant sensitivity parameters vary a lot in construction control.In this way,structural security and stability of a project can be ensured in the course of construction.