Loss of preload of unprotected bolted joints considering environmental effects: A comparative study

Abstract

An experimental program, with the aim to investigate and understand the preload loss behaviour of single-bolted double-lap joints subjected to environmental effects, was conducted in this paper. Four bolt types including plain bolts, galvanised bolts, stainless steel bolts and glass fibre reinforced polymer (GFRP) bolts were investigated and three environmental scenarios (i.e. indoor, outdoor and seawater immersion) were covered to represent varying degrees of environmental severities. Steel bushes attached with strain gauges were used to obtain strain variations continuously for such bolted joints with various bolt types under different environments. Severer environments clearly introduced earlier and higher preload loss. The bolted joints with galvanised bolts and stainless steel bolts showed larger preload loss compared to those using plain bolts in seawater immersion scenario; and the preload of joints with GFRP bolts dropped to nearly zero after a certain time of exposure under seawater immersion scenario. Modelling work was then developed to describe the preload loss over time, where the effects from environmental scenario (outdoor and seawater immersion scenarios) and bolt type (plain, galvanised and stainless steel bolts) were considered and also the initial rapid preload loss can be considered.