Steel Buildings in Europe

Part 4: Detailed Design 4 – 43 The design of the members in any bracing system is generally straightforward. However, the following specific points need to be addressed: 5.4.1 Tension only systems Figure 5.14(a) shows nominally statically indeterminate systems with cross bracing. In practice, the diagonal members are likely to have a high slenderness (either as flats or as small angles to minimise intrusion into the building). The contribution from the compressive diagonal is therefore ignored. 5.4.2 Load reversal in statically determinate bracing systems Figure 5.14 (b), (c) and (d) show examples of statically determinate bracing systems. The loading on most bracing systems is fully reversing. It is therefore only necessary to design the diagonals for the more critical condition, when the member is in compression. 5.4.3 Typical bracing members Bracing members are connected using nominally pinned joints and therefore they carry axial loads only. Bracing members can be welded or bolted to the main structural members. For bolted connections, use of normal (non-preloaded) bolts is generally appropriate for bracing in the scope of this guide (up to 12 storeys). Typical sections used as bracing include flats, angles and channels. Flat bar Two calculations must be carried out to determine the tension resistance of flat bars:  Gross section resistance, by using equation 6.6 of EN 1993-1-1. The partial factor to be used in this equation is  M0 .  Net section resistance, by using equation 6.7 of EN 1993-1-1. The partial factor to be used in this equation is  M2 . The compression resistance of flats should be carried out by following the method given in EN 1993-1-1, § 6.3.1. Angles When the bolts are positioned on the centroid of the section, the tension resistance of angles may be carried out as described for flat bars. When the bolts are positioned away from the centroid of the section the following procedures may be adopted. Single line of bolts along the member Where there is a single line of bolts along the angle and the bolts are not aligned with the centroid of the section, there is an additional bending moment due to the eccentricity. EN-1993-1-8, § 3.10.3 gives rules for the calculation of the tensile resistance in this case.