Detection of beam-end fractures in steel members based on local stiffness calculated by strain response

Abstract

Detecting structural damage from earthquakes is a vital aspect of disaster response for ensuring the continued safe use of affected building structures. In this paper, a method is proposed for detecting beam-end fractures after earthquake vibrations. In this proposed method, an index called local stiffness is used, which is defined as the ratio of the bending moment amplitude at a focused section in the first-mode vibration to the deformation amplitude of the structural frame. When a fracture occurs near the focused section, the local stiffness decreases significantly owing to the decrease of the moment transfer ability of the section. Thus, beam-end fractures are located by detecting drops in the local stiffness near a fracture. This method was applied to data measured in a shaking table test of a two-story steel moment frame, where beam-end fractures were observed after several excitations using earthquake ground motions. The time history of the local stiffness values obtained during the test demonstrated large decrease in values around the times of the fracture occurrences. Moreover, the local stiffness values could be calculated with adequate accuracy, even from the measured data without strict time synchronization. The local stiffness value was determined to be an effective tool for fracture detection based on simple time-series physical measurements.