Durability of FRP-Steel Lap Joints

Abstract

The long term durability of FRP repaired steel structures is crucial for their safe use and effective design. Past studies that investigated the durability of FRP-steel single lap joints have focused on their response under extreme temperature and curing conditions, but without representing the actual on-site conditions for typical civil engineering applications. This research presents an experimental investigation into the effects of hygrothermal cycles and sustained loading on steel-CFRP bonded lap joints under typical environmental conditions. A total of 84 steel-CFRP single lap joints and 126 Epoxy specimens were prepared and exposed to five hygrothermal cycles and sustained loading conditions. Specimens that survived the long-term loading were then tested to failure for evaluating their residual strength. The temperature cycles ranged from 15oC to 50oC and the relative humidity ranged between 40-70% under different combinations. These practical ranges of hygrothermal cycles were combined with realistic curing temperatures and curing times. Sustained loads that equal to 30% and 50% of the failure loads were also applied. The results show that exposure to hygrothermal conditions only has little impact on the bonding strength. However, when hygrothermal and sustained loading were applied simultaneously, the bond strength of the lap joints was significantly affected in some circumstances.

The thesis starts with a background that includes the different type of FRP application on the field as well as the modes of failure commonly found in steel-FRP composite application. The factors that affect the durability of the lap joints are discussed as well. It is then followed by a critical literature review of the most related studies on the durability of steel-CFRP lap joints. Next, existing classical models that are used for the analysis of lap joints are discussed and compared. The models are then used to provide an approximate prediction of the expected failure loads in the experimental study. The experimental plan and results are then collated and discussed in detail followed by the main conclusions of the thesis.