Theory of seismic response analysis of steel-concrete composite structures using fiber beam elements

For the consideration of accuracy, broad applicability, efficiency, rapid and stable numerical solution, as well as powerful and convenient pre-processing and post-processing, the customization of the large generic FE package MSC.MARC (2005r2) is proposed to combine the fiber section model and the displacement-based perfectly-bonded beam element with distributed plastic hinges, resulting in a fiber beam element for seismic response analysis of steel-concrete composite structures. Based on the characteristics of composite sections usually used in practice, the definition approach of composite sections and the discretization process of section fibers are proposed. The solution algorithm of the sectional constitutive law is also derived. The uniaxial constitutive laws of the concrete, steel and reinforcement materials are focused on. The proposed concrete constitutive model covers the ordinary, high-strength and confined concrete material. Based on some previous models which can only reflect the strength degradation phenomenon due to single unloading and reloading, the hysteretic law is improved to consider the strength degradation phenomenon due to repeated unloading and reloading so that the model can more reasonably and accurately trace the actual complex nonlinear behavior of the concrete material in composite members subjected to the real seismic action. The adopted steel and reinforcement material model can consider the Bauschinger effect rationally.