Research On Shear Lag Effect Of Continuous Rigid Frame Bridge With Single Box And Double Cells During Construction

Continuous rigid frame bridges are being used more and more widely in China,With the increase of the number of lanes,the application of single-box double-cell continuous rigid frame bridges in China has been gradually increased.Cantilever construction is used in most domestic prestressed continuous rigid frame bridges.Therefore,the shear lag effect of the single-box double-cell main beam is significant during the construction process.If the shear lag effect during construction is neglected,it may affect the safety of the entire bridge structure.In this paper,the Renjiang River Bridge(single box and double cells continuous rigid frame bridge)of Zunyi City with a main span of 120 m is studied for engineering support,the finite element model of the Renjiang River Bridge is established by using the finite element method and bar finite element.The variation law of shear lag effect in the cantilever construction of single box double-cell continuous rigid frame bridge is analyzed.The main contents are as follows:(1)Based on the energy variational method,a general expression of a single-box single-chamber box girder is derived assuming a longitudinal displacement of k times.The governing differential equation of the section of single box and double cells box girder is established,and the expression of stress calculation is derived,and several formulas of shear lag effect of double cells box beam with equal section are solved.(2)Based on the measured data of the Renjiang River Bridge,the variation of the normal stress of the top and bottom plates at the mid-span section of the single-box double-cell box girder with the construction stage is analyzed.(3)The MIDAS/CIVIL and MIDAS/FEA finite element models of the Renjiang River Bridge were established to analyze the shear lag effect of the main sections with different construction conditions.The variation law of shear lag coefficient of beam section in construction stage with construction conditions is summarized.Several different load-action models were established to analyze the variation of shear lag coefficient under self-weight and pre-stress.It is found that prestress has the greatest influence on the shear lag effect of box girder.(4)Taking the cantilever root section of Renjiang River Bridge as the reference section,different spatial solid models and bar system models are established,and the geometric parameters,such as width to span ratio,width to height ratio,roof thickness and web thickness,are analyzed.Effect of support size on shear lag effect of single box and double cells box girder.The effects of different loads,such as concentrated force and uniform force,on the shear lag effect of box girder are analyzed.Through the research of this paper,the following conclusions are drawn:(1)The shear lag effect of the single-box double-cell continuous rigid frame bridge has been in existence throughout the construction process.The concrete pouring and prestressed tension in the cantilever construction stage have a significant effect on the shear lag effect.When the concrete is poured,the shear lag effect will be aggravated,and the prestressed tension will reduce the shear lag effect;(2)The mid-span and the second-stage dead load will reduce the shear lag effect.(3)Through parameter analysis,it is found that the wide span ratio and the aspect ratio have a great influence on the shear lag effect.The support size has a great influence on the shear lag.The thickness of the web and the roof has no significant effect on the shear lag effect.