Part 1: Architect’s Guide 1 - 19 The span ranges for the various structural options for floors are shown in Table 4.3. Table 4.3 Span ranges of various structural options Span (m) 6 8 10 13 16 20 Reinforced concrete flat slab Slim floor beams and deep composite slab Integrated beams with precast slabs Reinforced concrete beams and slab Post-tensioned concrete flat slab Composite beams and slab Fabricated beams with web openings Cellular composite beams 4.2 Bracings 4.2.1 General A structure is statically determinate when the number of supports is just enough to ensure its global stability. By increasing the number of supports and rigid connections, the structure becomes stiffer, but rigid connections are more expensive than simple connections. So an economic compromise has to be found. Table 4.6 shows two options for the stability in a vertical plane of a multi-storey building. Braced structure The global stability is ensured by cross bracing (see § 4.2.2). Simple connections are used. The bracing members in compression are generally ignored in the detailed design. Frame effect The global stability is ensured by frame effect (see § 4.2.3) thanks to the stiffness of the connections. This solution leads to more complex connections. Figure 4.10 Global stability in vertical planes of a multi-storey structure The stability of a building has to be ensured in all the main planes (vertical and horizontal planes) in order to transfer the forces to the foundations, as shown in Figure 4.11.
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