A finite element model for collapse and long-term analysis of steel-concrete composite beams

This paper concerns the development of a numerical procedure for studying steel–concrete composite beams with regard to both the collapse analysis and long-term behavior at the serviceability limit state. The interaction among different parameters that affect the beam response, i.e., connection flexibility, rheological phenomena of concrete (creep and shrinkage), and nonlinear behavior of component materials (concrete cracking, nonlinear behavior of connection, yield of reinforcement, and yield of steel beam), is adequately considered by a uniaxial finite element model. The creep of concrete is taken into account using Maxwell’s generalized rheological model through a step-by-step time increment procedure. The nonlinear behavior of component materials is considered through a new nonlinear iterative procedure called the ‘‘modified secant stiffness method,’’ particularly effective for this type of problem. Some comparisons with experimental results demonstrate the reliability of the proposed formulation and its capability to predict the real structural behavior in both short-term tests under the collapse load and long-term tests under the service load.