Research On The Shear Lag Effect And The Effective Distribution Width Of Single Box Three-cell Girder

Due to the increasing number of passenger and freight traffic,people have paid more and more attention to the capacity of passenger and freight traffic of bridge which is an important component of road traffic,therefore,the use of single box multi-cell box girder bridge construction is also gradually increased.Aimed at three-cell box girder bridge,this paper studied the effect of shear lag and the effective width of flange on the load minutely.The main results are as follows:(1)Based on the essence of shear lag effect of box girder,the warping displacement function is defined by combining with the characteristics of three-cell box girder,and the governing differential equations of equilibrium for the shear lag are established,and taking a set of simply supported box girder as an example,shear leg of three-cell box girder under concentrated force and uniform force is research by considering its boundary condition.By comparing the calculated results with the finite element results,the rationality of the warping displacement function is proved.(2)In actual use,box girder bear various load at the same time,the paper use concentrated load and uniform load and prestressing load to form combined load,studied the shear leg of three-cell box girder under combined load.The results showed that the transverse distribution of shear lag under concentrated force and uniform force is between those two loads alone works;the transverse distribution of shear lag in top deck under concentrated force and prestressing force coincide with the result when concentrated load alone works,the shear lag effect of the floor plate is more obvious than that two loads alone works;the transverse distribution of shear lag in top deck under uniform force and prestressing force coincide with the result when uniform load alone works,the shear lag effect of the floor plate is more obvious than that two loads alone works.(3)The rule about box girder effective flange width in Highway reinforced concrete and prestressed concrete bridge design code is based on the data of single room box girder,and the code does not stated whether the specification is applicable to single box multi-cell box girder,this paper take three-cell box girder as an example,using ansys parametric design language defined some parameters(including the width and thickness of the top and floor of the box girder,the height of the box girder,the span,etc),determined the range of parameters,and he value of each parameter is determined by computer and a large number of ANSYS finite element models are generated,and the correctness of the model is verified by comparing the mid-span deformation of two different element and same size models.(4)For simply supported single box three-cell box girder,200 models were generated randomly,data of effective distribution width of flange on mid span position and support position was calculated according to the definition of effective distribution width of flange,and the curve is obtained by data fitting.By comparing the curve with the corresponding curve in code,it is found that the standard curve is not suitable for simply supported single box girder to determine its effective distribution width of flange.(5)For continuous single box three-cell box girder,200 models were generated randomly,data of effective distribution width of flange on mid span position and middle support position and edge support position was calculated according to the definition of effective distribution width of flange,and the curve is obtained by data fitting.By comparing the curve with the corresponding curve in code,it is found that the standard curve is not suitable for continuous single box three-cell box girder to determine its effective distribution width of flange.(6)According to the idea of the guarantee rate of the soil strength,Corrected the fitting curve about effective width of three-cell box girder,made more than 95% of the sample points lie on the right side of the curve,so that the safety of the structure can be guaranteed in the case of more than 95%,and given the comparison of the correction curve with the standard curve and the formula of modified fitting curve.