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

The Paper identifies a major problem that can arise, owing to the ampl ification of edge stresses by shear lag, in the lower flange of a cont inuous steel box girder in the region of the internal supports. The so lutions 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 longitu dinal stiffeners. The alternative solution proposed for strengthening an existing bridge girder is to add a concrete layer to the compressio n flange so that it acts compositely with the steel. Results are prese nted to show the effectiveness of the proposed solutions.