Steel Buildings in Europe

Part 4: Detailed Design of Portal Frames 4 - 15 where: L is span of frame (see Figure 3.7) h is the height of the lower column at either end of the span being considered (see Figure 3.7)  cr is the elastic critical buckling load factor. If the axial load in the rafter is significant (see Section 3.3.1),  cr,est should be calculated in accordance with Appendix B). Other frames should be designed using second order elastic-plastic analysis software. Amplification factors Category A: Regular, symmetric and nearly symmetric pitched and mono-pitched frames (See Figure 3.7). Regular, symmetric and mono-pitched frames include single span frames and multi-span frames in which there is only a small variation in height ( h ) and span ( L ) between the different spans; variations in height and span of the order of 10% may be considered as being sufficiently small. In the traditional industrial application of this approach, first-order analysis may be used for such frames if all the applied actions are amplified by        cr 1 1 1  , or          est cr, 1 1 1  if the axial force in the rafter was found to be significant. h L L h 1 2 L L h 3 1 Mono-pitch 2 Single-span 3 Multi-span Figure 3.7 Examples of Category A frames