Modified-Weibull-stress-based evaluation of brittle fracture occurrence during earthquakes in steel members

Abstract

Brittle fractures can originate from shallow surface cracks on welded parts of steel structures during earthquakes. Since the occurrence of such fractures is significantly influenced by the shape of the welded parts, the existing methods based on material testing cannot predict fractures. This study focused on a modified Weibull stress, which considers the processes of nucleation and propagation of microcracks at different depths, and demonstrated its applicability to the evaluation of brittle fracture initiation during earthquakes. The demonstration was implemented on three types of structural steel using low-temperature experiments and numerical stress analyses on crack tips. Additionally, the independency of the obtained critical modified Weibull stress from the initial crack depth, strain rate and prestrain was examined in the prediction of the critical crack-tip opening displacement. Finally, the relationship between the critical deformation of the beam-to-column connection of a steel bridge pier at the fracture time (in the case of a fracture originating from a shallow crack) and its weld toe radius was quantitatively evaluated as an example of actual use of the modified-Weibull-stress-based evaluation.