Steel Buildings in Europe

Part 2: Concept Design 2 - 45 5.3 Long-span composite beams with web openings 5.3.1 Description Long span com posite beam s are often designed with large web openings to facilitate integration of services, as shown in Figure 5.5. Grids are eithe r arranged so that the lo ng span secondary beam s are placed at 3 m to 3,75 m spacing and are supported by shorter sp an prim ary beams. Alternatively, short-span secondary beams (6 - 9 m span) are supported by long-span primary beams. Service openings can be circular, elongated or rectangular in shape, and can be up to 70% of the beam de pth. They can have a length/depth ratio typically of up to 3,5. Web stiffeners may be required around large openings. Figure 5.5 Beams with various opening sizes and with off-site fire protection 5.3.2 Beam spans and design criteria Long-span secondary beams: 9 m to 15 m span at 3 m to 3,75 m spacing. Long-span primary beams: 9 m to 12 m span at 6 m to 9 m spacing. A typical structural arrangem ent whic h elim inates internal co lumns is illustrated in Figure 5.6. Elongated or r ectangular openings should be lo cated in areas of low shear, e.g. in the middle third of the span for uniform ly loaded beams. Other guidance on opening sizes is presented in Figure 5.7. Critical checks for long span beam s are usually deflections and dynam ic response. Shear resistance at large openings close to the supports or point loads m ay be critical.