AD 255: Design of Asymmetric Cellular Beams: Application limits of SCI Publication P-100

Cellular beams have become the vogue for many long span applications both in the UK, and increasingly in France. Often cellular beams are designed in buildings with strict height limitations such as in renovation applications, or in the French experience, to compete directly with concrete flat slab construction. To satisfy both serviceability requirements and the need to install reasonably large service ducts, cellular beams are increasingly designed with highly asymmetric sections and large openings off-centre with respect of the beam depth. In addition, the size of the bottom Tee, cut from a rolled steel section, can be increased disproportionately to the top Tee to achieve the required natural frequency limit. In such cases, there is a considerable reserve in bending and shear resistance for these long span beams.

From the structural design point of view, these new designs of cellular beams have moved considerably from those envisaged in the SCI publication P-100. SCI is working with European partners in an ECSC project to prepare application rules for composite beams with rectangular and circular openings consistent with Eurocode 4. SCI publication P-100 is used as the basis of design, but it is also necessary to extend the application to cover a wider range of design cases, one of which is the use of highly asymmetric composite cellular beams. Furthermore, both Eurocode 3 and BS 5950 Part 1: 2000 now increase the design shear resistance that can be developed in the Tees by at least 10% (due to the increase of the 0.9 factor on shear area to 1.0), and so it is necessary to have more accurate methods of analysis consistent with the higher stresses permitted by these new Codes.

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