Steel Buildings in Europe

Part 2: Concept Design 2 - 23 If diagonal bracing in the elevations cannot be accommodated, longitudinal stability can be provided by a rigid frame on the elevation, as shown in Figure 3.7. 1 2 1 Eaves strut 2 Rigid frame Figure 3.7 Rigid frame alternative to vertical bracing 3.3 Member stability Member stability should be checked using expressions 6.61 and 6.62 of EN 1993-1-1. For economic design, restraints to the rafter and column must be considered. The purlins and side rails are considered adequate to restrain the flange that they are attached to, but unless special measures are taken, the purlins and side rails do not restrain the inside flange. Restraint to the inside flange is commonly provided by bracing from the purlins and side rails, as shown in Figure 3.8. The bracing is usually formed of thin metal straps, designed to act in tension, or from angles designed in compression if bracing is only possible from one side. If the bracing shown in Figure 3.8 is not permitted by national regulations, restraint may be provided by a system of hot-rolled members. This form of bracing will be required whenever the inside flange is in compression. This situation arises:  On the inside of the column and the inside of the rafter in the haunch region, in the gravity load combination  Towards the apex of the rafter, in the uplift combination.