Steel Buildings in Europe

Part 4: Detailed Design 4 – 44 Multiple bolts across the member Where there is more than one bolt across the section, EN 1993 does not give guidance to account for the eccentricity. In order to account for the additional bending moment the designer has two options:  To use the interaction equations 6.61 and 6.62 of EN 1993-1-1  To use other recognised sources of information, such as Steel building design: Design data [12] , which provides an alternative method to account for this effect. The compression resistance of angles should be calculated by using the method given in § 6.3.1 of EN 1993-1-1. Where bolts are located away from the centroid of the section, the eccentricity will generate an additional bending moment on the member. As previously described for the tensile resistance of angles, this bending moment can be accounted for in two ways:  By using the interaction equations 6.61 and 6.62 of EN 1993-1-1  By calculating a modified slenderness as given in EN 1993-1-1, Annex BB 1.2 and applying it to the method given in § 6.3.1. If the angle is welded instead of bolted, the forces distribute across the member and no bending effects needs to be considered. When the bracing consists of unequal angles, it is important to specify which leg is connected. Channels The tension and compression resistances of channels are carried out in a similar way to that described for angles. Channels are invariably connected through the web, either by welding or by means of bolts. This introduces an eccentricity with respect to the centroid of the section. Although EN 1993-1-1 does not explicitly allow the use of Annex BB 1.2 for the compression resistance of channels, the authors suggest that the approach may also be used for this purpose. When channels with thin webs are used, bearing of the bolts on the channel may be critical. In order to avoid this problem the designer may specify larger bolts or the web of the channel may be thickened by welding a plate on the web. 5.5 Horizontal bracing Horizontal bracing, or at least floor diaphragm action, is necessary to transmit horizontal forces and requirements for horizontal restraint to planes of vertical bracing. Where triangulated steel bracing is adopted, the design approaches are essentially the same as those for vertical bracing. However, in general, it is more economical to use the floor as a diaphragm.