Steel Buildings in Europe

Part 4: Detailed Design 4 – 25 5 ULTIMATE LIMIT STATE 5.1 Introduction Design for the Ultimate Limit State, i.e. verification of the strength of all the structural components of the building to resist the actions identified by the global analysis, remains the core of the detailed design process. Fortunately, many design aids are now available to assist designers; these have relieved them of much of the detailed effort that was previously required. The following sections provide comprehensive guidance on how to take full account of these aids, while still providing reference back to their basis in the Eurocodes. 5.2 Floor systems 5.2.1 Floor slab Either a composite slab or a precast floor will have been chosen during conceptual design. Both may be designed from first principles but this is rarely, if ever, done in practice. A composite slab may be designed to EN 1993-1-3 [1] for the construction condition, EN 1994-1-1 [2] for the completed structure and EN 1994-1-2 for the fire condition. A precast reinforced concrete floor may be designed to EN 1992-1-1 [7] . All these standards make provision for design assisted by testing, in accordance with Annex D of EN 1990 [5] . For such specialist construction products with wide application in practice, the design assisted by testing route has been adopted by the manufacturers because it offers greater design resistance than that determined by calculation. Manufacturers supplying into a national market will usually offer appropriate design tables which take full account of Nationally Determined Parameters defined in relevant National Annexes. Designers should use these design tables wherever they are available. 5.2.2 Downstand non-composite beams Downstand non-composite floor beams are used to support precast floor systems, and, possibly, composite floor slabs that are not attached to their supporting beams by shear connectors. Downstand roof beams generally carry the purlins that support roof systems Depending on the details of construction, these beams may be:  Fully restrained for both construction and in-service conditions.  Restrained at points of load application for both construction and in-service conditions.