Ultra-low cycle fatigue test study of bolted spherical joints in steel grid structures

Abstract

During a catastrophic earthquake, bending and failure were exhibited in the bolted spherical joints, and these phenomena have obvious ultra-low cycle fatigue (ULCF) failure characteristics. To study the failure characteristics, hysteresis behavior, stiffness degradation, and energy consumption of bolted spherical joints, the ULCF test of bolted spherical joints specimens was carried out. The experimental study showed that the high-strength bolts experienced an ULCF failure process of bending, crack initiation, crack propagation, and instantaneous failure, and the fatigue life of the specimens was less than 20 times. The pinch phenomenon in the hysteresis curve of the specimen was significant, indicating that its energy consumption was poor. The energy-damage model of the specimens under cyclic displacement was derived based on the cumulative energy consumption. A damage assessment method for the specimen was proposed based on the energy-damage model and angle change characteristics of the specimen. This method provides a reference for damage assessment and repair design of bolted spherical joint grid structures after an earthquake.