Steel Buildings in Europe

Part 4: Detailed Design of Portal Frames 4 - 23 6 MEMBER STABILITY 6.1 Introduction Members must be checked for the combined effects of axial load and buckling. In general, this will be by satisfying Expressions 6.61 and 6.62 of EN 1993-1- 1, as described in Section 6.2. In the special circumstances where there are plastic hinges in members, EN 1993-1-1 gives particular requirements, as described in Section 6.4. In-plane buckling is buckling about the major axis of the member. As explained in Section 6.1.1, there are no intermediate restraints when considering in-plane buckling of a member in a portal frame. Out-of-plane buckling concerns buckling about the minor axis of the member. In a portal frame the secondary steelwork can be used to provide restraints, and so increase the buckling resistance, as described in Section 6.3. 6.1.1 Member buckling in portal frames N N 1 4 3 2 M M 1 2 1 Intersection with column at eaves 2,3 Intersection with purlins (typical) 4 Apex of frame Figure 6.1 Diagrammatic representation of a portal frame rafter Figure 6.1 shows a simple representation of the issues that need to be addressed when considering the stability of a member within a portal frame, in this example a rafter between the eaves and apex. The following points should be noted:  There can be no intermediate points of restraint for in-plane buckling between the main nodes of the frame, 1 and 4.  Intermediate restraints may be introduced (nodes 2 and 3) against out-of-plane buckling.