Steel Buildings in Europe

Part 4: Detailed Design of Portal Frames 4 - 31 Figure 6.6 Decision tree for selection of appropriate stable length criteria in a portal frame – Sheet 3 6.5 Design summary Before proceeding to the detailed verification of rafter and column stability, designers should appreciate that:  Torsional and lateral restraints need to be provided at all hinge positions, as required by § 6.3.5.2.  EN 1993-1-1 recognises four different types of stable lengths, L stable , L m , L k and L s , adjacent to plastic hinge positions. Lateral restraints must be provided adjacent to the hinge at no greater distance than L stable or L m and torsional restraints at no greater distance than L k or L s , as appropriate.  In zones where there is no plastic hinge, each member must satisfy the simplified forms of Expressions 6.61 and 6.62. These consider in-plane and out-of-plane stability and their potential interaction.