STRENGTHENING STEEL BOX-GIRDER BRIDGES BY CONTROLLING THE EFFECTS OF SHEAR LAG

The Paper identifies a major problem that can arise, owing to the amplification of edge stresses by shear lag, in the lower flange of a continuous steel box girder in the region of the internal supports. The solutions proposed recommend that in the design of a new box girder the required buckling resistance of the flange in these compressive zones is achieved by an increase in flange thickness, rather than by longitudinal stiffeners. The alternative solution proposed for strengthening an existing bridge girder is to add a concrete layer to the compression flange so that it acts compositely with the steel. Results are presented to show the effectiveness of the proposed solutions.