A deformation limit based on failure assessment diagram for fatigue-cracked X-joints under in-plane bending

Abstract

This study develops a deformation limit based on the failure assessment diagram (FAD) for fatigue-cracked circular hollow section (CHS) X-joints subjected to brace in-plane bending. The proposed approach calibrates against two reported experimental tests on CHS X-joints. The subsequent numerical study considers CHS X-joints with two different brace-to-chord intersection angles. The parametric study focuses on both the material toughness level and the geometric parameters. The proposed, dimensionless deformation limit covers a wide range of material fracture-toughness and geometric parameters. The option 1 and option 3 failure assessment curves provide consistent deformation limits compared to the toughness-based deformation limits proposed in a previous study. The lower bound deformation limit exhibits an approximately linear relationship with respect to the crack-depth ratio for X-joints with different brace-to-chord intersection angles. The extrapolated deformation level at a zero crack-depth ratio represents a conservative estimation on the deformation level for intact joints.