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The Chairman: ' I wonder if the authors could answer a very simple question: prior to the meeting they gave me an explanation of the savings which were made, and mentioned certain weights of steel that were involved, how many of these structures are designed or have been designed in this way, and what is the potential for the future? '
The work described in this paper provides a rational basis for the determination of effective widths taking the parameters relevant to the geometry and materials properties in the section into account, assuming the absence of slip between the steel joist and the concrete slab. Harmonic series solutions are employed in the determination of effective widths for various side ratios of the slab and various ratios of the slab thickness to the depth of the steel beam. These solutions incorporate the variation of the neutral axis depth across the width of the wide concrete flange due to shear lag effect. Three standard steel sections were used as the basis of the computations. A general computer program that requires the dimensions of the steel joist and the slab has been developed. The case considered is that of a simply supported symmetrically loaded system of a slab spanning several equally spaced identical steel ribs. The loading consists of central point loads on all ribs, the dead load of the composite section being taken into account in the computations.
The collapse mechanisms and the ultimate load equations to be considered in the limit design of uniformly loaded continuous slab and beam floors are examined. It is shown that the beams may be designed on the basis of the distribution of the loading on the adjacent segments of the yield-line pattern for collapse of the panels alone, rather than by the consideration of composite collapse mechanisms. The use of approximate loading distributions is shown to lead to unsafe design of the beams.