Steel Buildings in Europe

Part 2: Concept Design 2 - 26 It may be assumed for preliminary design that I C = 1,5  I R Given the bending moments around the frame, the rafter should be chosen so that the moment resistance exceeds both the moment at the “sharp” end of the haunch and the maximum sagging moment (a little larger than the moment at the apex). 3.4.2 Gable columns Gable columns are generally designed as simply supported from base to rafter. The primary loads are the wind actions. The internal pressure or suction will contribute to the loading on the gable column. Often, the critical design case will be pressure inside the building and suction on the outside, when the inside flange of the gable post is unrestrained. If national regulations allow, a restraint to the inside flange may be provided from a sheeting rail to increase the buckling resistance. 3.4.3 Bracing At the preliminary design stage, it is convenient to calculate the overall longitudinal load on the structure. This shear must be the horizontal component of the load carried by the vertical bracing. The most heavily loaded roof bracing will be the member nearest the eaves. The longitudinal eaves member carries the load from the roof bracing to the vertical bracing. Bracing members may be hollow sections, angle sections or flat steel. Flat steel is assumed to resist tension forces only.