Steel Buildings in Europe

Part 4: Detailed Design 4 – 48 Figure 6.1 Strategies for accidental design situations 6.2 Consequence classes As mentioned above, Appendix B.3 of EN 1990 defines three consequence classes: CC1 Low consequences of failure CC2 Medium consequences of failure CC3 High consequences of failure Class CC2 is subdivided by EN 1991-1-7 [13] into CC2a (Lower risk group) and CC2b (Upper risk group). Medium rise buildings mostly fall within group CC2b, the criteria for which are reproduced Table 6.1. Table 6.1 An example of building categorisation (taken from Table A.1 of EN 1991-1-7) Consequence Class Example of categorisation of building type and occupancy Hotels, flats, apartments and other residential buildings greater than 4 storeys but not exceeding 15 storeys Educational buildings greater than single storey but not exceeding 15 storeys Retailing premises greater than 3 storeys but not exceeding 15 storeys Offices greater than 4 storeys but not exceeding 15 storeys CC2b Upper Risk Group All buildings to which the public are admitted and which contain floor areas exceeding 2000 m 2 but not exceeding 5000 m 2 at each storey EN 1991-1-7, § 3.2 and § 3.3 provide a wide range of possible general strategies for identified accidental actions and for limiting the extent of localised failure respectively. Apart from structures at specific risk from impact (EN 1991-1-7 Section 4) or internal explosion (EN 1991-1-7, § 5), this publication recommends that design of low and medium rise building structures in Consequence Class CC2b should generally involve the design for localised failure (see Section 6.3 of this document). The design of columns as key elements (see Section 6.4) is only appropriate where not all columns are continuous through to the basement; for example where they are supported by a transfer structure.