Off-torque and long-term performance of bolted joints for structural disassembly and reusability

This paper presents the performance of single-bolted double-lap joints after long-term service of up to 12 months in various environments for structural disassembly and reusability. Two commonly used steel bolts (i.e. M20 class 8.8 plain bolts with black oxide finish and hot-dip galvanised bolts) and a M20 glass fibre polymer bolt were considered. Three scenarios (i.e. indoor, outdoor and seawater immersion) were included to cover a range of environmental severities. The torques required to initiate the disassembly (i.e. off-torque) after such environmental exposures were originally obtained. The corroded steel plates were reclaimed for reassembly of bolted joints using new bolts. Tensile tests were then conducted for such reassembled joints and compared with the intact ones, in terms of failure modes, load-displacement and strain responses. It was found that a harsher environment introduced severer steel corrosion and greater increase in off-torque. The bolted joints with hot-dip galvanised bolts showed larger increase (i.e. around 77%) in off-torque compared to those using plain bolts (i.e. around 12%) after exposure to seawater immersion for 12 months; while the off-torque for joints with glass fibre polymer bolts nearly remained stable, with a reduction of around 10%. Both reassembled and intact joints exhibited the plate bearing failure around bolt hole and curling at the cover plate end on the bolt head side, regardless of the exposure periods, environmental scenarios, or bolt types. Similar joint capacity and stiffness were observed for the reassembled joints with steel or glass fibre polymer bolts in reference to their intact counterparts.