Cold bending steel beams: a state-of the-art engineering solution that meets industry challenges

Abstract

Cold bending practice in the steel bridge industry is ambiguous. AASHTO allows cold straightening and cambering, but not curving. AASHTOs major concern is loss of fracture toughness (CVN) of the base metal and cracking of the weld due to fatigue. Alternatively, heat curving is widely used. Controversy in heat curving appeared as a recent study by Texas DOT on the effects of bending on the ductility of flange plates showed that when heat was applied to assist in the bending operation, particularly to reduce the bending forces, bridge fabricators have, on occasion, experienced the formation of cracks in the flange plate. Moreover, results showed that for heat-assisted bending operations, strain levels above 10 percent reduced the ductility and fracture toughness of the plate. Such controversy and unjustified reluctance for adopting cold bending for curving has jeopardized steels competitive advantage in curved bridge applications, especially High Performance Steel (HPS) which demonstrates a high yield strength, high toughness and high formability in cold bending. An urgent need was therefore identified by steel fabricators to use cold bending for curving for efficiency, economy and time saving. A simple, versatile and cost-effective proprietary cold curving process was developed for this purpose and systematized by deriving closedform solution that relate bending loads to curvatures. Its applicability and accuracy were verified based on comparisons with experimental results from a full-scale test girder. Visual inspection did not identify any localized damages, signs of distress or fracture which prove the legitimacy of cold bending within certain strain limits.