Steel Buildings in Europe

Part 4: Detailed Design 4 – 12 Figure 2.5 shows two cases, both of which give rise to a horizontal shear force of  N Ed . Note that in this case, the value of  is calculated using a value of  h that is appropriate to the height of only a single storey and that, since the value of N Ed is different above and below the floor, the larger value (i.e. that for the lower storey) should be used. 2.7.4 Imperfections at splices EN 1993-1-1, § 5.3.3 states that imperfections in the bracing system should also be considered. Whereas most of the clause is applicable to bracing systems that restrain members in compression, such as chords of trusses, the guidance on forces at splices in § 5.3.3(4) should be followed for multi-storey columns. h h h N N N N N Ed Ed Ed Ed Ed       = = H H i i /2 /2 Figure 2.5 Configuration of sway imperfection  for horizontal forces on floor diaphragm (taken from EN 1993-1-1, Figure 5.3) The lateral force at a splice should be taken as  m N Ed /100, and this must be resisted by the local bracing members in addition to the forces from externally applied actions such as wind load but excluding the equivalent horizontal forces. The force to be carried locally is the summation from all the splices at that level, distributed amongst the bracing systems. If many heavily-loaded columns are spliced at the same level, the force could be significant. Assuming that a splice is nominally at a floor level, only the bracing members at that floor and between the floor above and below need to be verified for this additional force. This is shown in Figure 2.6. This additional force should not be used in the design of the overall bracing systems and is not taken to the foundations, unless the splice is at the first storey. When designing the bracing system, only one imperfection needs to be considered at a time. When checking the bracing for the additional forces due to imperfections at splices, the equivalent horizontal forces should not be applied to the bracing system.