Fiber Beam Element Formulation Using the Softened Membrane Model


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Title: Fiber Beam Element Formulation Using the Softened Membrane Model

Author(s): R.T. Mullapudi and A.S. Ayoub

Publication: Special Publication

Volume: 265


Appears on pages(s): 283-308

Keywords: fiber model; force-based finite element; shear critical; softened membrane model; Timoshenko beam.

Date: 10/1/2009

This study presents an inelastic nonlinear beam element with axial, bending, and shear force interaction for cyclic analysis of reinforced concrete (RC) structures. The element considers shear deformation, and is based on the section discretization into fibers with hysteretic material models for the constituent materials. The shear mechanism along the beam is modeled by using a Timoshenko beam approach. The steel material constitutive law is assumed to be bilinear. The concrete constitutive law is based on the soften membrane model. This newly developed constitutive law can predict the concrete contribution Vc, which is produced by the shear resistance of concrete along the initial crack direction. The constitutive relationships of the RC element have been developed based on the smeared behavior of cracked continuous orthotropic material assumption of concrete with the inclusion of Poisson effects. This model accounts for the softening effect of concrete, as well as the tension stiffening and confining effects. Transverse strains are internal variables determined by imposing equilibrium at each fiber between concrete and vertical transverse steel reinforcement. Element forces are obtained by performing an equilibrium-based numerical integration on the section axial, flexural, and shear behaviors along the element length. The paper concludes with a correlation study between the analytical models and experimentally tested shear-critical RC columns.