This paper presents results from the first three years of an investigation into the durability of bonded coated steel joints under tropical conditions. Three different steels are being evaluated, bonded with three epoxy adhesives, and joints are being exposed with and without imposed stress. The uncoated mild steel joints exhibited poor durability. The retained strength of unstressed joints declined rapidly as the extent of bondline corrosion increased. Failure times of stressed joints were rapid and also due to bondline corrosion except when a more flexible adhesive was used, failure then being due to creep of the adhesive. The durability of the electrogalvanized and zinc-nickel coated steel joints was generally much better, the retained strengths were higher and the failure times of stressed joints were usually longer. This is mainly attributed to the absence of bondline corrosion. However, ft was found that coating failure sometimes occurred with the zinc-nickel coated steel when bonded with the stiffer adhesives. This affected both the initial strength and the durability of joints, although the degree of coating failure was seen to reduce as exposure time increased.
