Steel Buildings in Europe

Part 2: Concept Design 2 - 64 Class CC2 is subdivided by EN 1991-1-7 into CC2a (Lower risk group) and CC2b (Upper risk group). Medium rise buildings mostly fall with group CC2b. Examples of categories given by Tabl e A.1 of EN 1991-1-7 include the following: Table 6.1 Examples of building categorisation (taken from Table A.1 of EN 1991-1-7) Consequence Class Example of categorization of building type and occupancy 2B Upper Risk Group 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. 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. The recomm ended strategy for Conse quence Class 2b involves either the design for localised failure (see Section 6.1.2) or the design of colum ns as key elements (see Section 6.1.6). 6.1.2 Design for the consequences of localised failure in multi-storey buildings In multi-storey build ings, the requ irement for r obustness g enerally leads to a design s trategy where the colum ns are tied in to the rest of the s tructure. This should m ean that any one length of column cannot easily be removed. However, should a len gth be removed by an acciden tal action, th e floor systems should be able to develop catenary action, to lim it the extent of the failure. It should be noted that the requ irements are not intended to ensur e th at th e structure is still serv iceable following some extreme event, but that da mage is limited, and that progressive collapse is prevented. 6.1.3 Horizontal tying EN 1991-1-7, A.5 provides guidance on the horizontal tying of fra med structures. It gives expressions for th e design tensile resistance requ ired for internal and perimeter ties. The calculated tying force is generally equal to the vertical shear. Tying forces do not necessarily need to be carried by the steelwork fram e. A composite concrete floor, for example, can be used to tie columns together, but must be designed to perfor m this fu nction. Addition al reinforcement may be required, and the columns (particularl y edge colum ns) m ay need careful detailing to ensure the tying force is transferred between column and slab. If the tying forces are to be carried by the structural steelwork alone, it should be noted th at the check for tying resis tance is entirely s eparate to that f or resistance to vertical forces. The shear force and tying forces are never applied