Steel Buildings in Europe

Part 2: Concept Design 2 - 31 3.6.3 Portal frame with overhead crane Figure 3.19 Crane portal frame with column brackets For cranes of relatively low capacity (up to say 20 tonnes), portal frames can be used to support the crane beam and rail, as illustrated in Figure 3.19. The outward movement (spread) of the frame at the level of the crane rail is likely to be of critical importance. Use of a horizontal tie member or fixed column bases may be necessary to reduce this spread. For larger cranes, a structure with a roof truss will be appropriate (see Section 4) as the column spread is minimised. For very heavy loads, built-up columns are appropriate, as introduced in Section 6. Detail design guides cover both the design of trusses [3] and the design of built-up columns [4] . 3.6.4 Tied portal frame 1 2 1 Tie 2 Hangers (required for longer spans) Figure 3.20 Tied portal frame In a tied portal frame, as illustrated in Figure 3.20, the spread of the eaves and the bending moments in the frame are greatly reduced. Large compression forces will develop in the rafters, which reduce the stability of the members. Second-order software must be used for the design of tied portals.