Remarks to the Direct Strength Method

The effects of local plate buckling on the load carrying capacity of thin walled members are usually accounted for by the established method of effective widths. As a consequence, the current design concepts of such members are often complicated. Part of these complications arise from the need to determine effective properties of members. Therefore Schafer and Pekِz developed the Direct Strength Method as an alternative to current practice. A strength curve for the entire member is used similarly to the strength curve for the effective width of an element. rect Strength Method is here compared to the approaches of effective width, reduced stress and effective thickness. A more profound understanding of the methodʹs conception can be gained on this basis. As a result, the Direct Strength Method assumes the plastic reserve of the section shape to influence the cross-section capacity of locally buckled members. This assumption is checked by our own tests on thin-walled I-sections. A proposal to extend the Direct Strength Method to the interaction between axial force and bending is presented in a second step. Here, the limitations of the method will become clear. Particularly, the Direct Strength Method may lead to an overestimation of the ultimate load, if a shift of the effective centroid causes an additional bending moment. For the time being, the Direct Strength Method can therefore not be a general design concept and further investigations are necessary.