A unified nonlinear structural analysis framework based on a degrading hysteretic beam element model

In this work, a unified structural analysis framework is presented, which is able to efficiently characterize the nonlinear behavior of a variety of different structural elements under relevant loads, including seismic loading conditions. A concise and fully parametrized degrading hysteretic beam finite element (DHBE) stands at the core of the suggested formulation. The developed DHBE is able to describe several types of nonlinearities and hysteretic behaviors of both Euler and Timoshenko type elements, while preserving its overall formulation, by merely varying some parameter values. Indicatively, unsymmetrical yielding, non-uniform strength and stiffness degradation, and pinching phenomena of beam elements can be straightforwardly described in an integrated manner. More specifically, nonlinearities are defined at the element level in terms of hysteretic curvatures, axial and shear deformations, which are set to evolve according to Bouc-Wen type evolution equations. New evolution equations and nonlinear parametric functions have also been developed in this work to incorporate additional degradation phenomena in a consistent manner. Additionally, distributed plasticity is accounted for by appropriate hysteretic shape functions. One of the main advantages of this modeling framework is that the typically used time-dependent tangent stiffness matrix is not required in this case, but is instead replaced by one elastic and one hysteretic stiffness matrix, both invariant with time. The computational efficiency, versatility and robustness of the suggested model is illustrated through numerical examples and comparisons with experimental data from available tests.