Element mesh, section discretization and material hysteretic laws for fiber beam-column elements of composite structural members

A fiber beam-column element for nonlinear analysis of composite structural members is developed in this paper. The programing of complex material uniaxial constitutive laws and the implementation of the developed element into a general commercial standard finite-element package are discussed. Intensive parametric studies on the modeling strategies of element mesh, section discretization and material hysteretic laws are carried out to develop fiber element with sufficient accuracy, efficiency, stability and practicality for composite structural members. Rational element mesh scheme is recommended to capture the sharp jump of the curvature value at the plastic hinge region and to effectively overcome the numerical difficulty of pathological mesh-sensitivity brought about by the strain softening effect. Efficient section discretization schemes are proposed to give results of sufficient accuracy for the hysteretic behavior of composite members under complex cyclic load histories. The Bauschinger effect of the steel is found to be the most significant factor dominating the accuracy, and the hysteretic law of the concrete can be simplified by ignoring the complex strength and stiffness degradation effects with little influence on the accuracy. Finally, the developed program COMPONA-MARC and the recommended modeling strategies are validated by extensive experimental results of composite structural members.