Experimental and numerical investigations on residual stresses in hot-bent circular steel tube

Abstract

Residual stress is always present in steel structures and can cause a premature plasticity of the steel and considerably affect the stiffness, ultimate bearing capacity, and fatigue resistance of members or joints. This paper presents experimental and numerical investigations on residual stresses in a hot-bent circular steel tube. Longitudinal residual stresses are measured through a cutting method. The residual stress distribution is symmetrical for both extrados and intrados of a hot-bent circular tube. The maximal tensile or compressive residual stress occurs at the extrados or intrados near the neutral axis of steel tubes. A parametric study with 54 numerical models is then conducted to investigate the influencing factors of the residual stress (e.g. bending ratio, diameter-to-thickness ratio, and steel yield strength). According to the results, the bending ratio (as the most important factor) has a significant influence on the residual stress distribution and magnitude. The results imply that the residual stress and diameter-to-thickness ratio exhibit no distinct correlation. The hot-bent circular tubes with higher steel yield stresses exhibit greater residual stresses. The effects of the yield strength fy can be simplified in the form of the residual stress multiplied by fy/345. Finally, the residual stress model of the hot-bent circular tube is proposed as a polyline formation. It fits the actual residual stress distribution well when the self-equilibrium characteristics are considered.