Steel Buildings in Europe

Part 4: Detailed Design 4 – 16 If the recommended values of NDP are adopted, it will be found that the option of using expressions (6.10a)/(6.10b) is generally less onerous than using (6.10). It will also be found that, apart from storage areas, (6.10b) is the more onerous of (6.10a) and (6.10b), unless the permanent action is much (4,5 times) greater than the variable action. This is most unlikely in a multi-storey framed building. Three types of combination of actions at the serviceability limit state are considered – characteristic, frequent and quasi-permanent. Expressions for these are given in 6.14b, 6.15b and 6.16b, as follows:        1 0, k, 1 k,1 k, G i i i j j Q P Q  6.14b        1 2, k, 1 1,1 k,1 k, i i i j j Q G P Q   6.15b       1 2, k, 1 k, i i i j j G P Q  6.16b It is implicit in these expressions that partial factors are equal to unity. The factors for accompanying actions (  0 ,  1 and  2 ) are given in EN 1990 [5] , but the National Annex may give additional information as to what values should be used. These values are specific for the type of load being considered, i.e.  1 for snow is different from  1 for wind. For braced multi-storey building frames, the serviceability limit states to be considered will normally be those for the vertical and horizontal deflections of the frame and the dynamic performance of the floors. Crack widths may also need to be controlled for durability reasons in some situations (such as in car parks) and occasionally for appearance reasons. Guidance is given in EN 1992-1-1 [7] and in Multi-storey steel buildings. Part 3: Actions [6] . 3.3 Analysis for gravity loads With the assumption of pinned behaviour for beam/column connections, all floor systems adopted for multi-storey buildings are statically determinate. Simple load allocation may be adopted to determine the governing moments, shears and axial forces in all elements: floors slabs, secondary beams, primary beams, columns and connections. EN 1991-1-1, § 6.2.1(4) defines the reduction factor,  A , that may be applied to gravity loads on floors, beams and roofs according to the area supported by the appropriate member. § 6.2.2(2) defines an equivalent factor,  n , for gravity loads on walls and columns, depending on the number of storeys loading the appropriate element. Not all imposed gravity loads qualify for the reduction. For example, it would not be appropriate where:  Loads have been specifically determined from knowledge of the proposed use