DYNAMIC RESPONSE OF RC STRUCTURES INVESTIGATED THROUGH AN ENHANCED BEAM FINITE ELEMENT WITH DAMAGE AND PLASTICITY

Abstract eng:
Despite significant advances in computer technology and the increasingly accurate computational models developed during the last decades, the mechanical behavior of large scale structure is still a challenging task. In particular, civil engineering structures subjected to seismic actions deserve special efforts, as the dynamic response to ground motions is strongly influenced by the materials complex nonlinear behavior. Force-based and mixed beam-column finite elements (FE) have been widely adopted for structural nonlinear response simulations, because of their efficiency over classical displacement-based approaches. These are also preferred to bi-dimensional (2D) and three-dimensional (3D) FE formulations, thanks to the considerable reduction of the computational burden. Beam-column models with material nonlinearities have been proposed to reproduce the response of steel, reinforced concrete (RC) and composite frames. However, very few efforts have been dedicated to investigate the influence of shear and torsional effects in the nonlinear dynamic response of framed structures. This work presents a 2-node 3D beam-column finite element, based on an enhanced Timoshenko beam theory. This is based on an enriched kinematic description, partially removing the rigid sections and accounting for out-of-plane deformations [1, 2]. The model introduces the material nonlinear behavior through the definition of a cross-section fiber discretization, which allows the description of the full multiaxial coupling of the stress components. A 3D plastic-damage constitutive model is used to describe the degrading response of the material. Two different variables are defined to reproduce the damaging processes for tensile and compressive strain states. Moreover, a Drucker-Prager plasticity formulation is introduced to account for the plastic strain growth. The adoption of the 3D material model provides a better description of the interaction between the shear and axial stresses/strains. The required procedure for condensing out the stress components that are irrelevant for the beam formulation is performed with an optimized non-iterative scheme. Hence, a very efficient and fast solution algorithm is developed and implemented in the Matlab toolbox for FE analyses FEDEASLab. The presented correlation studies adopt the proposed FE procedure to investigate the seismic response of RC structures, especially when shear/torsional deformations significantly influence the overall failure mechanism. The numerical results are compared with experimental outcomes and with the solutions obtained from standard FE models.

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