Steel Buildings in Europe

Part 4: Detailed Design 4 – 13 1 2 1 Level of splice 2 Local members to be verified for additional force arising from (in this case) 5 splices Figure 2.6 Bracing members to be verified at splice levels As the force may be in either direction, it is advised that the simplest approach is to divide the force into components (in the case above, into the two diagonal members) and verify each member for the additional force. Note that the values of the imperfection forces and the forces in the members due to wind load vary, depending on the combination of actions being considered. 2.7.5 Member bow imperfections In a braced frame with simple connections, no allowance is needed in the global analysis for bow imperfections in members because they do not influence the global behaviour. The effects of local bow imperfections in members are taken into account in the design of both compression members and unrestrained beams through the use of appropriate buckling curves, as described in Section 6 of EN 1993-1-1. 2.7.6 Design recommendations for imperfections Based on the background studies presented in Access Steel document SN047a [4] , it is possible to make the following simple, safe recommendations for design. (More direct application of EN 1993-1-1 could reduce the design imperfection forces by 50% in some circumstances, but the forces are normally small). 1. Apply equivalent horizontal forces of 1/200 of vertical forces at floor and roof levels. Storey shears at any level in the building will be 1/200 of the total forces above (the summation of the EHF above that level). These forces should be considered in all relevant horizontal directions but need only be considered in one direction at a time. (In accordance with EN 1993-1-1, § 5.3.2(10), the possible torsional effects on a structure caused by anti-symmetric sways at the two opposite faces should also be considered. This effect is only significant in a building of