On the analysis of fracture phenomena observed in steel structures during the Kobe earthquake

Abstract

During the Kobe earthquake, brittle fracture occurred in some of the steel structures. From the observation of fracture surface, the process of the brittle fracture is considered to occur as a sequence of three events: ductile crack initiation, ductile crack growth, and brittle crack propagation. This implies that the ductile crack initiation plays an important role in the brittle fracture. As a first step to assess the brittle fracture, this chapter examines the applicability of a finite element method (FEM) analysis based on the void damage theory to the simulation of the initial ductile failure. To deal with the ductile fracture under cyclic loads, such as seismic loads, the conventional void damage theory based on the Gurson model is modified to take into account the kinematic hardening rule in addition to the isotropic hardening rule for the constitutive relation of the base material. By the comparison between the FEM analysis and experiment, the chapter shows that the location of the ductile fracture in steel columns can be predicted by the FEM analysis based on the void damage theory. This implies that a lot of improvisation is needed in order to quantitatively predict the process of the ductile fracture under cyclic loading.