Linear Control And Secondary Internal Force Analysis Of The Main Girder Of The Prestressed Concrete Continuous Rigid Frame Bridge

With the rapid development of transportation in China,the prestressed concrete continuous rigid frame bridge is widely used because of its good structural characteristics.However,the internal force and alignment of the main girder of the continuous rigid frame bridge constructed by hanging basket cantilever are constantly changing due to the influence of internal and external factors in the construction process.Therefore,it is necessary to control the internal force and alignment in the construction process of the bridge.On the other hand,the continuous rigid frame bridge belongs to the statically indeterminate structure,after the bridge closes,there are many structural system transformations,temperature and prestressing force Under the action of various factors,the structure will produce larger secondary internal forces.Therefore,relying on the monitoring project of the PC continuous rigid frame bridge under construction,this paper analyses the alignment control and secondary internal force of the main girder of the PC continuous rigid frame bridge,and draws conclusions that can provide reference for the further optimization of the construction of the PC continuous rigid frame bridge.(1)Based on the engineering background of a continuous rigid frame bridge,this paper establishes the finite element model with Midas/civil bridge analysis software.Firstly,the calculation results of the alignment and stress of the main girder during the construction stage,ten years after completion of the bridge,moving load,foundation settlement and temperature load are analyzed.It is considered that the closure section construction is the key construction stage,and attention should be paid to the elevation of the formwork at the same time.The influence of concrete shrinkage and creep should be taken into account in the calculation.During construction,attention should be paid to temperature and foundation settlement to ensure that the alignment and stress of the main girder are within a reasonable range.(2)Taking the alignment of the designed bridge as the control objective,the method of controlling the elevation of formwork for continuous rigid frame bridge is analyzed.The pre-arch value and the deformation value of the hanging basket involved in the elevation of formwork are analyzed in detail.The method of calculating the pre-arch based on the forward algorithm is obtained.The alignment value of the completed bridge is compared with the theoretical value,and the result of the main girder alignment control is good.In addition,the influence of concrete bulk density,shrinkage and creep,elastic modulus,friction coefficient of pipeline wall,local deviation coefficient,tension control stress,position of prestressing tendon,relative humidity,cantilever construction period and second-stage paving time on the alignment of the main girder is analyzed.It is considered that the influence degree of each factor on the alignment of the main girder is different.The change of displacement value is slightly larger than the superposition of deflection change value with multi-parameters acting alone,and there is a certain combination effect between them.(3)The secondary internal forces generated by foundation settlement,temperature,prestressing force and concrete shrinkage and creep are extracted respectively with finite element software,and the numerical results of secondary internal forces are analyzed,and the advantages and disadvantages of the secondary internal forces caused by various factors on the structure are obtained.(4)The change of secondary internal force of the main girder during the operation period of the completed bridge when the tension control stress and the position of the prestressing tendons,the construction period of cantilever casting,the second stage paving time and the relative humidity change in the construction control factors.It is concluded that with the increase of operation period,secondary bending moment increases,the closer the position of tension control stress and prestressing tendon is to the center line of box girder,the greater the secondary bending moment,and vice versa.The change of cantilever construction period has a certain influence on the secondary internal force of creep of beam concrete.The longer the construction period,the smaller the secondary internal force produced by creep.Considering the economic benefits,it is appropriate that the construction time of cantilever casting is 7 days.The change of construction time of second stage pavement has little effect on the secondary moment of creep caused by long-term creep,but the earlier the end of construction period,the better the initial force of bridge.This is the case.The construction environment between 70%and 80%relative humidity is beneficial to the midspan position of the main girder.