Environmental Durability of CFRP Strand Sheets Strengthened Steel Plate Double Strap Joints

Steel bridges exposed to aggressive environments such as coastal conditions can experience damage due to various deterioration mechanisms. One of the most important threats during lifetime of a steel bridge structure is the corrosion. The deterioration of steel bridges due to corrosion decreases the lifespan and reliability of the system and leads to reduction in serviceability and aesthetics of the structure. In addition, with the incorporation of new legal load models into load rating process, many existing short to medium span steel bridges are now rated as structurally deficient in live load capacity. Therefore, many state transportation agencies need to strengthen steel bridges due to increases in live loads or loss of capacity as a result of environmental deterioration. Fiber reinforced polymers (FRPs) have been widely considered to restore stiffness and strength of concrete bridges due to their favorable properties such as high corrosion resistance, lightweight and high tensile strength. However, their applications to steel bridges have been limited. Several studies showed that the use of high modulus carbon FRP (CFRP) laminates or sheets can significantly increase both the ultimate flexural capacity and the stiffness of steel beams, but the premature debonding failure was commonly observed. More recently, a new form of CFRPs that consists of small-diameter strands have been shown to possess excellent bond characteristics and great potential for flexural and shear strengthening of steel girder bridges through laboratory investigations. However, the environmental durability of steel members strengthened with CFRP strand sheets has not been studied yet.
This study investigates the durability of CFRP strand sheet-steel plate double strap joints in accelerated corrosion conditions. The CFRP-steel double strap joint specimens with different bond lengths were fabricated. The specimens were subjected to different levels of accelerated corrosion conditions using an electrochemical method for three exposure durations corresponding to 5%, 10%, and 15% mass losses based on the Faraday’s law. Then, tensile testing of double strap joints was conducted on an MTS frame up to failure. Results were analyzed in terms of bond strength, effective bond length and joint stiffness considering different exposure durations. Failure modes of specimens with different bond lengths and exposed to different levels of corrosion were also discussed.