Steel Buildings in Europe

Part 2: Concept Design 2 - 32 3.6.5 Mansard or curved portal frames Figure 3.21 Mansard portal frame A mansard portal frame consists of a series of rafters and haunches, as illustrated in Figure 3.21, which creates a pseudo-curved frame. The connections between the members may also have small haunches to facilitate the bolted connections. Curved rafter portals as illustrated in Figure 3.22 are often used for architectural applications. The rafter can be curved to a radius by cold bending. For spans greater than approximately 18 m, splices may be required in the rafter because of limitations of transport. Alternatively, a curved external roof must be produced by varying the lengths of purlin brackets supported on a rafter fabricated as a series of straight elements, as shown in Figure 3.23. Figure 3.22 Curved beams used in a portal frame