Shear Lag Effect in Simply Supported Prestressed Concrete Box Girder

In this paper, derivation and computed formulas are provided for the shear lag coefficient in a simply supported prestressed concrete box girder under dead load. In the case of prestressed tendons having parabolic configurations, formulas to compute the shear lag effect are also developed. The magnitude of upward loading intensity caused by prestress as well as the relationship between the height of the box girder and the sag of prestressed tendons have been fully treated. Conclusions are drawn that the shear lag effect caused by dead load and prestress force is equivalent to dead load acting alone, provided that the prestressed tendon is set up with a parabolic profile. Shear lag effect caused by movable load is also analyzed according to the eccentricity of the load to the half-width ratio of the box girder. Charts were prepared to predict the shear lag coefficient for live load. Finally, having considered the shear deformation of flanges, the deflection of box girders is studied for both uniformly distributed load and concentrated load. Examples are given for illustrative purpose.