Enhanced 3D Fiber Beam-Column Element with Warping Displacements

Abstract eng:
Beam elements are commonly used in the analysis of steel and reinforced concrete structures in earthquake engineering practice. These elements reproduce the global behavior of these structures at a reasonable computational cost. For this type of analysis the force-based fiber beam element has proven an excellent compromise between accuracy and computational cost for the simulation of the inelastic response of structural models of significant size. Recent studies have proposed extensions of the model to account for the effect of shear and torsion under fixed shear strain or stress distributions. These assumptions suffer from shortcomings for the representation of the coupling between shear and torsion, and are not suitable for the representation of local stress and strain distributions at critical sections. To describe such complex stress states, shell finite element models are often used with a significant increase in computational cost. This paper presents the mixed formulation of an enhanced 3d fiber beam element that represents accurately the global and local response of structural members under axial force, flexure, shear and torsion interaction. The proposed 3d fiber beam element determines the shear strain distribution at a section from the satisfaction of local equilibrium equations with the section warping displacements as local parameters. Unlike existing models, the coupling between sections is taken in account. Hence the enhanced fiber beam-column is able to capture the local effects due to constrained warping of the section, such as the flange shear lag effect. The model is also capable of representing accurately the maximum local stress at element boundaries, and of simulating the torsional response of beams under warping constraints. The element is validated with several examples involving inelastic response of steel members under high shear force, such as shear links. The simulations are conducted under monotonic and cyclic load conditions for specimens with wide flange and box sections. The accuracy and computational efficiency of the proposed element is demonstrated by comparing the results with experimental values and with local response estimates of shell finite element models.

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