Once a web panel has buckled, its capacity to carry additional diagonal compressive stresses is ignored and it is assumed that a new load-carrying mechanism s developed, whereby any additional shear load is carried by an inclined tensile membrane stress field. This tensile force anchors against the top and bottom flanges and against the transverse stiffener on either side of the web panel. The resistance offered by the web plates is analogous to that of the diagonal tie bars in the truss.