Hot-Dip Galvanized Hollow Structural Sections – Crack Prevention and Mechanical Behaviour
The application of hot-dip galvanized cold-formed Hollow Structural Sections (HSS) in exposed steel structures (e.g. bridges, transmission towers and sign supporting structures) is extremely popular due to their superior strength-to-weight ratio, low initial cost, sustainability and aesthetics. Both HSS manufacturing and hot-dip galvanizing techniques have evolved over the years. However, the use of newly developed zinc bath mixtures together with thick-walled HSS resulting in significant damage in the latter in the form of cracking during the galvanizing process, especially at comer regions of Rectangular Hollow Sections (RHS), has been reported to be a widespread problem lately [Packer et al. 2010]. In an even worse case, if such cracks do not cause visible damage to the section and remain undetected before the final product leaves the galvanizing shop, they can result in serious consequences on the performance of the structure.
This research aims to investigate the conditions which lead to cracking of hot-dip galvanized cold-formed HSS. More specifically, the following will be investigated: (1) the prerequisites of cracking; (2) if hot-dip galvanizing-induced embrittlement is a concern for RHS with different cross-sectional dimensions and produced to different specifications; (3) the thresholds of wall thickness above which different levels of pre-galvanizing countermeasures for brittle cracking are needed; and (4) the detrimental/beneficial effects of hot-dip galvanizing on the mechanical behaviours of RHS.
The long term goals of this project are to provide guidelines to engineers, fabricators and galvanizers to minimize the risk of cracking in RHS during hot-dip galvanizing; generate supplemental rules to HSS manufacturing specifications and crack control guidelines; and, provide a better understanding of the characteristics and structural performance of hot-dip galvanized RHS to facilitate its application.
Packer, J.A., Chiew, S.P., Tremblay, R. and Martinez-Saucedo, G. (2010). “Effect of Material Properties on Hollow Section Performance”, Structures and Buildings, Institution of Civil Engineers, Vol. 163(SB6), pp. 375-390.
Dr. Min Sun is an Assistant Professor in the Department of Civil Engineering at the University of Victoria. He received his B.Sc. (2008) from Tongji University, China, and his M.Eng. (2010) and Ph.D. (2014) from the University of Toronto. Before joining the faculty of the University of Victoria, he worked as a structural designer at Read Jones Christoffersen. Dr. Sun’s current research focus is on cold-formed steel structures.