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

Abstract

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. This research examined the changes in bolted joint strength in fiber-reinforced polymer (FRP) structures over time due to various factors such as bolt type, joint material, and environmental conditions. Our findings revealed that even after 30 years, the joints maintain strength well above the standard required, ensuring long-term reliability. This is particularly important for structures for which safety and durability are crucial, such as bridges and buildings in seismic areas. The study also highlights that specialized coatings and treatments, such as phosphate or galvanized surfaces, have a minimal effect on joint strength. This suggests that simpler, cost-effective methods can be employed without compromising safety. This has practical implications for construction and maintenance, offering ways to extend the life of existing structures and reduce the costs for new ones. By understanding these factors, engineers can design safer, longer-lasting FRP joints, contributing to more sustainable infrastructure development. This research provides valuable insights into enhancing the longevity and performance of bolted joints, ensuring that these critical connections withstand the challenges posed by time and environmental factors.