The Structural Effect Analysis Of Vertical Forced Closure For PC Continuous Rigid Frame Bridge And Jacking Force Optimization

This paper mainly studies and discusses the Engineering problems causing by vertical closure errors when mainspan closuring during the cantilever construction of the PC continuous rigid frame bridge.In particularly include the following aspects.(1) By reading the relevant literature,it reviews the development of the PC continuous rigid frame bridge、Structural stress characteristics、characteristics of design and construction and the development trend of the PC continuous rigid frame bridge;It points out the importance of reserching vertical closure error’ effect on the structure,combined with the construction control and code requirement of continuous rigid frame bridge.(2) The construction error can be divided into precontrol and non precontrol errors.According to the error sources, the construction error can be classified into component property error、environmental factors error、consturction state error、accidental factors error.Scientific understanding ofclosure error is the key to prevent and reduce the closure error.(3) Starting from the basic principle of structural mechanics,the calculation formula of additional weight and the calculation formula of secondary internal force causing by the additional weight are derived.These formulas are verified by the engineering example.According to the calculation formula of additional pressure weight it could be found that additional pressure is related to material strength grade、span、pier height、section size、closure segment length and vertical closure error.Additional weight is proportional to the vertical closure error.In addition,combined with the construction process, the calculating formula of jacking force which is applied to three-span continuous rigid frame bridge is deduced.It lays the theoretical foundation for jacking force optimization.(4) Combined with the engineering example,using the finite element numerical analysis method,discussing that the additional weight affects on the deformation and internal force of girder and pier under three different conditions which include the stageof laying effect before mid-span closure、two dead load、three year creep.The analysis shows that the effect of additional pressure on the highside of the cantilever end is much larger than the bottom side of the cantilever end,and and the effect on the structure of high side cantilever end is adverse,beneficial to the other side structure. Through the analysis of the additional pressure’s effect on the structure, the sensitive parts of the structure is found and then relevant preventive reinforcement measures to prevent cracking of the beam is put forward.(5) Jacking force, which is applied before the continuous rigid frame bridge’closure is optimized from four angles including the bridge、shrinkage and creep of concrete、temperature effect、the additive pressure.Through the project example simulation,comparing whether applying the optimized jacking force or not,the result of pier deviation, internal forces and internal forces of the main beam,show that the optimized jacking force have a good improvement for the pier and main beam.(6) some issue about the form、location、size、and release method of counterweight are discussed.