Steel Buildings in Europe

Part 4: Detailed Design 4 – 51 If the tying forces are to be carried by the structural steelwork alone, the verification of tying resistance is entirely separate from that for resistance to vertical forces. The shear forces and tying forces are never applied at the same time. Furthermore, the usual requirement that members and connections remain serviceable under design loading is ignored when calculating resistance to tying, as ‘substantial permanent deformation of members and their connections is acceptable’. Guidance on the tying resistance of standard simple connections is presented in Multi-storey steel buildings. Part 5: Joint design [14] . Frequently, ties may be discontinuous, or have no ‘anchor’ at the end distant to the column. The connection is simply designed for the applied force. This situation is also common at external columns, where only the local design of the connection is considered. The column itself is not designed to resist the tying force. 6.3.4 Tying of precast concrete floor units EN 1991-1-7 § A.5.1(2) requires that when concrete or other heavy floor units are used (as floors), they should be tied in the direction of their span. The intention is to prevent floor units or floor slabs simply falling through the steel frame, if the steelwork is moved or removed due to some major trauma. Slabs must be tied to each other over supports and tied to edge beams. Tying forces may be determined from EN 1992-1-1 [7] , § 9.10.2 and the relevant National Annex. Tying across internal supports If the precast units have a structural screed, it may be possible to use the reinforcement in the screed to carry the tie forces, as shown in Figure 6.4, or to provide additional reinforcing bars. 1 1 Reinforcement in screed Figure 6.4 Screed with reinforcement Alternatively, it may be possible to expose the voids in the precast planks and place reinforcing bars between the two units prior to concreting, as shown in Figure 6.5.