Research On Shear Lag Effect Of PC Continuous Rigid Frame Box Girder

Because of the characteristics of long-span continuous rigid frame bridge,such as beautiful shape,large rigidity and strong spanning capacity,it is widely used in China.However,the large-span continuous rigid frame bridge mainly adopts box section with large section size,which has obvious spatial stress characteristics.There will be shear lag effect in the cantilever pouring stage and the completion stage of the continuous rigid frame bridge.If it is not considered properly,it will cause the top and bottom of the box girder Slab cracking,which affects the service life of the structure.At present,t the research on shear lag analysis and theoretical calculation of continuous rigid frame bridge is not perfect.Therefore,this paper takes the multi span single box single room PC Continuous Rigid Frame Bridge as supported bridge type.The shear lag effect of PC continuous rigid frame box girder is systematically studied by theoretical derivation and finite element numerical calculation.The study was concentrated on the following parts:1.The spring model of flange plate is established.Based on the energy variation principle,the form of warping displacement function of flange plate is derived as the linear combination of hyperbolic function and trigonometric function,which is verified by the finite element and test data.Finally,The warping displacement function adopts hyperbolic sine function with higher accuracy.2.Based on the assumption of plane section,the stiffness increasing coefficient of the section considering reinforcement is deduced,the warping displacement function correction coefficient of the section considering reinforcement is deduced by using the shear deformation law of flange plate and the conversion section method,and the shear lag control differential equation considering reinforcement is established.Through the analysis of an example,the calculation result of this paper is in good agreement with the calculation value of solid finite element,and influence law of reinforcement on the stress of flange plate is obtained.3.Based on the energy variational method,a simplified method for calculating the shear lag effect of PC continuous rigid frame with variable cross-section based on MIDAS/civil model internal force value and finite difference method is proposed.The derived warpage displacement function,warpage correction coefficient and stiffness increase coefficient considering reinforcement are substituted into the shear lag calculation formula of continuous rigid frame,and the comparative analysis is carried out by relying on the bridge type continuous rigid frame.And it is concluded that the method in this paper can calculate the shear lag coefficient of each section accurately and has good applicability.4.Taking a five span continuous rigid frame bridge as an example,MIDAS/civil and MIDAS / FEA are used to carry out numerical calculation.The stress distribution characteristics and shear lag coefficient distribution law of the key sections of the continuous rigid frame bridge in the cantilever pouring stage and the completion stage are obtained.The existence of prestressed duct will aggravate the shear lag effect during the construction of the first 8 beam section in the cantilever pouring stage,at the stage of completion,the unfavorable section of the whole bridge is obtained,which can provide reference for engineering design.