In steel industrial building, the usage of elements with web-tapered cross-section, made of welded thin plates is common. These low structure elements are generally designed using gravitational load combinations. Rafters and columns help shape the bending moment in gravitational load combination thus reducing the material consumption and reducing the structural self-weight. In case of an earthquake, low inertia forces are used in single-span industrial buildings. Thus not allowing the seismic design concept to impose a high structural ductility class. Within the framework of an RFCS research program, a simple chart based procedure to select the best seismic design concept for portal frames have been proposed. Depending on the frame geometry we may use a low-dissipative or dissipative concept. The method mentioned above indicates the fact that for most cases of portal frames with variable column and beam cross-sections, the optimal choice will be a low-dissipative concept. This helps eliminate the strict anti-seismic conditions referring to cross-section class, elements slenderness, imposed detailing conditions, etc. and conduct to a more effective cost of the building. The tapered shape of the element and high cross-section class of web wall is obtained at the end with the maximum height. The buckling capacity of such a slender member will be determined by the efficiency and position of the restraining elements, end support conditions and initial geometrical and material imperfections. At cross-sections members, used generally for columns elements, restrained against lateral or/and torsional buckling, the coupling between sectional capacity and overall elastic buckling of the members in compression and/or in bending may occur. In certain section members, found at the rafter highest section of the tapered web, local buckling of the walls or distortion may appear in elastic domain. For member which are not laterally restrained or the restrains are not effective, the global failure mode of the members will be characterized by the lateral-torsional mode, either alone or in interaction with local buckling.