Elastoplastic Cross-Sectional Behavior of Composite Beams with High-Strength Steel: Analytical Modeling

Composite steel-concrete beams that use high-strength (HS) steel sections are more sustainable from an environmental low-carbon perspective than those that use mild steel because less steel is needed. Quantifying the elastoplastic cross-sectional behavior of composite beams using HS steel sections is important because HS steel has significant differences in its plastic properties when compared with conventional mild steel. It is also important to establish this behavior in order to apply the principles of rigid plastic design. This paper develops a new analytical model for the cross-sectional analysis of HS steel-concrete composite beams to elucidate this elastoplastic response, so as to ascertain the validity of applying rigid plastic design. Both material nonlinearity and partial shear connection are incorporated in the analysis. The constitutive model for the steel is specified by using a multilinear stress-strain relationship, and that of the concrete is based on a model in terms of its axial stress-strain relationship that is prescribed in Eurocode 4. The slip strain between the steel and concrete components at the interface is treated as being dependent on the curvature and the degree of shear connection. The equation of horizontal equilibrium is derived, from which the curvature and the corresponding strain distribution through the depth of the cross-section can be obtained, leading to the bending moment resisted by the cross section. Comparisons with experimental results, those from rigid plastic analysis as well as with numerical solutions, demonstrate that the analytical procedure is adequate and accurate, providing a much-needed analytical solution for establishing the moment-curvature response of composite beams with HS steel. (C) 2014 American Society of Civil Engineers.