Variable Cross-section Concrete Thin-walled Box Girder Shear Lag Effect Studies

Based on theoretical analysis and finite element method, the paper investigates the shear lag effect of box girder bridges with variable cross sections. It concentrated on calculating the shear lag coefficient and effective flange width coefficient in different combinations of loading. Two examples of prestressed concrete continuous box girder bridges with variable cross sections are involved. The result of example 2 is presented to compare the precision of effective flange width in the standards of China. Germany and US. Moreover, some sensitive factors such as width-length ratio, girder height ratio, loading arrangement and the section's location are analyzed.The conclusions are as follows:The spatial FEM can relatively accurately reflect the stress of the practical structure. The shear lag effect of box girder bridges can't be neglected. With regard to effective flange width, the standard of Germany (DIN 1075) is more accurate, however National Standard (JTJ023-85) is apt to be exaggerated. The shear lag effect is seriously effected by width-length ratio, girder height ratio, loading arrangement and the section's location. The shear lag effect of the continuous box girder bridges with width-length ratio less than 0.05 is not obvious, whose effective flange width can be ignored. The shear lag effect of the section under concentrated load is more remarkable than that of other sections. National Standard (JTJ023-85) is worth discussing further.