During propped construction the steel-concrete composite action resists dead as well asimposed loads. Conversely, the steel section alone resists the floor self-weight in unproppedbeams. The major difference between propped and unpropped composite beams lies in theductility requirements rather than in the strength requirements. Relatively few studies havebeen carried out to assess the rotation requirements for unpropped semi-continuouscomposite beams. The outstanding critical factor in the case of unpropped construction is thedead load stress that must be carried by the steel beam alone prior to hardening of theconcrete.This research overcomes the difficulties involved in modelling the composite and noncompositestages by using a numerical integration technique developed from the basicprinciples of structural mechanics. The method incorporates the fully non-linear materialproperties and requires very little assumption. The technique was initially validated using theexperimental results from plain steel beam bending tests. The subsequent comparisonbetween the model predictions and the results from the large-scale frame test carried out forthis research purpose, showed that the method is capable of predicting non-elastic load vs.end rotation behaviour within a high degree of accuracy. Thus the model can be used withconfidence in order to predict the connection rotation requirements for a wider range ofloading configurations than is practically possible from experimental testing alone.A parametric study is carried out using the numerical integration technique developed for thesemi-continuous composite beam on a total of 2160 different beam configurations, utilisingdifferent steel grades and loading conditions. In this study the influence of dead load stress onthe connection rotation requirement has been thoroughly evaluated along with several otherfactors including span to depth ratio, location within the building frame, ratio between the support (connection) moment capacity and span (beam) moment capacity, loading type, steelgrade and percentage of the beam strength utilised during design. The connection rotationcapacity requirements resulting from this study are assessed to establish the scope forextending the use of composite connections to unpropped beams.The large-scale experiment that has been carried out provided an opportunity to investigatethe behaviour of a modified form of composite connection detail for use at perimetercolumns (single-sided composite connections) with improved rebar anchorage.Additionally, another extensive parametric study is carried out using the numericalintegration technique developed for the steel beam to establish the influence of strainhardeningon elastic-plastic frame instability design.
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