Hybrid joints: laboratory vs. field conditions

This paper investigates the performance of hybrid joints combining adhesive bonding and pretensioned bolts on steel substrates, taking into account imperfections. In an optimal laboratory setting involving clean steel surfaces and curing in accordance with the technical datasheets, hybrid joints bonded with Scotch-Weld 7240 (SW7240) achieved a load capacity of around 352 kN, whereas those bonded with SikaDur 370 (S370) reached approximately 394 kN. These results provide a basis for evaluating joint performance under various imperfect real-world conditions. The study also explores how surface preparation, exposure to saltwater and temperature variations impact joint performance. For bare steel surfaces treated under suboptimal conditions, joints exposed to saltwater and cleaned with a grinding fleece had a maximum load capacity of 320 kN with SW7240, while joints cleaned with a 50% isopropanol/demineralised water mixture had a maximum load capacity of 325 kN. This illustrates a slight reduction compared to ideal conditions. Curing temperature also influences joint performance. S370 joints on a galvanised surface, manufactured at 40°C, demonstrated an average load capacity of 272 kN - a significant improvement on the 143 kN observed for joints bonded at 5°C - indicating an increase in performance of over 89%. Furthermore, the results suggest that exposure to saltwater negatively affects the load-carrying capacity of joints, with a decrease of around 30% for S370 joints compared to reference samples bonded under optimal conditions. Notably, hot-dip galvanised surfaces exhibited consistent load capacities of approximately 259 kN for the SW7240 and 167 kN for the S370, demonstrating resilience against different surface preparation methods. These findings emphasise the importance of understanding how real-world conditions, such as surface imperfections, exposure to saltwater and temperature fluctuations, affect the reliability of adhesive bonding in structural applications. The study highlights the resilience of hybrid joints towards imperfections and reduces the need for strict industry standards regarding adhesive use and surface preparation in construction.