COUPLED INSTABILITY AND NEGATIVE SHEAR LAG PHENOMENON IN BOX GIRDERS

The explanation of the negative shear lag phenomenon in linear analysi s of box girders is reviewed, The extension of the analysis to include geometrical nonlinear effects in a compression flange, due to bucklin g in both classical and negative shear lag environments, is presented. It is shown that in interaction the buckling and the negative shear l ag have opposite effects on longitudinal stress distribution across th e flange and, depending on load level, both the effects ave effectivel y damped out. However, the overwhelming significance of buckling near the peak loan may be expected. The important influence of flange trans verse stiffeners and the very unusual distribution of longitudinal str esses in box girder webs in the negative shear lag region are also men tioned.