Variational principle usually applied in shear lag effect analysis of box girder. In the paper, base on transformed-section method, adopting variational principle, it deducing shear lag coefficient formulation of simply supported prestressed concrete box girder under uniform load and simply supported reinforced concrete box girder under concentrated load, concrete cracking is considered in shear lag effect, and compared with experimental result and design code. It is clear in mechanical concept to analyze shear lag effect of cracked concrete box girder by variational principle, it is the exten...
