Long-Term Relaxation Characteristics of Hot-Dip Galvanized High-Strength Bolted Frictional GFRP Joints: An Experimental Study

The bolt axial force of high-strength bolted frictional glass fiber–reinforced polymer (GFRP) joints is reduced by the viscoelastic behavior of the GFRP matrix resin. In this study, the long-term relaxation characteristics of GFRP joints with hot-dip galvanized, coated connecting plates were clarified. Long-term relaxation tests were performed by varying the connecting conditions and material properties, such as the presence or absence of the GFRP coating, applied bolt axial force, presence or absence of hot-dip galvanization and surface treatment of the connecting plates, GFRP base member thickness, and fiber content. Phosphate treatment of the galvanized steel plates exhibited a negligible effect on the relaxation properties of GFRP joints. The bolt axial force reduction rate was accelerated by utilizing hot-dip galvanized plates or GFRPs with low fiber contents. This study provides insights into the long-term relaxation characteristics of GFRP joints with specific coatings, thus contributing to safer, more durable, and cost-effective infrastructure solutions, while also fostering advancements in materials science and engineering.