摘要：The design of composite steel and concrete beams should normally include the progressive deterioration in strength and stiffness of its components (steel section, concrete slab and shear connectors) with temperature rise under fire. In European Prestandard Eurocode 4, a simple calculation method is described where the assessment of the composite beam strength consists of two different steps: first the calculation of temperature distribution versus time in the cross-section and then the determination of the mechanical behavior to estimate the load-bearing capacity of the member. In this work, a study is described to verify if the simplifications allowed by Eurocode 4 to obtain the temperature rise in the components of composite beams comprising steel beams with no encasement may lead to inappropriate design. Two programs were developed for the analysis: the first, a heat transfer code, for the determination of the temperature distribution in each region of the composite beam; the second, a structural analysis program, for designing the composite beam. As an example, a composite beam has its positive bending moment strength determined under the temperature calculated numerically as well as the temperature obtained with the simplifications. The strength results are compared and discussed.
