Rotation capacity of I-beams under cyclic loading with different kinematic/isotropic hardening characteristics

Abstract

Deformation of buildings during strong earthquakes can be mitigated by energy dissipation of structural members. Generally speaking, buildings are designed to have Strong Column – Weak Beam (SC-WB) action. Therefore, plasticized beam behavior is important. To realize the designed energy dissipation of the beam, buckling must be prevented up to the designed story drift. Beam stability is dictated by geometric and material nonlinearities. Geometric nonlinearity is ascertained from the evaluation equations that incorporate consideration of the beam section, length, and initial imperfections. The Young's modulus and yield stress obtained from tensile test results reflect the material properties of steel. Therefore, the evaluation rarely reflects the influence of material characteristics in the plastic region under cyclic stress. Faced with this concern, this study first applies cyclic material tests to various steel grades and loading protocols. The hardening parameters of Voce–Chaboche model are computed from data based on material test data. Then an investigation at the material level is conducted at the member level through cyclic loading tests of I-shaped beams having different steel specifications. Finite element analysis (FEA) results revealed differences in material behaviors. Finally, a parametric study of the steel plastic behavior is conducted using the experimentally validated FEA model. Based on data obtained from this study, a modification factor for the existing evaluation index is proposed to improve the accuracy of structural capacity evaluations.