Bond strength of sand-coated SMA rebars with mechanical couplers

This research evaluates the pullout test configuration and bond strength of sand-coated SMA rebars with different mechanical couplers. The study is divided into three phases, each corresponding to a specific objective. In the first phase, a pilot study was conducted to identify the optimal pullout test configuration for determining the bond strength between mechanical couplers and steel rebars. Three pullout test configurations were implemented namely Uniform Pullout Test (UPT), Direct Pullout Test (DPT), and Direct Tension Pullout Test (DTPT), each adopted from international standards. The results indicated that the DPT configuration provided the most consistent bond strength predictions compared to UPT and DTPT. Additionally, the results from Phase One reveal that the bond strength performance did not rely solely on the pullout test setup (e.g., clamp zone length); other factors such as bar diameter and coupler type also played a crucial role. Emanating from the outcome of Phase One will serve as the basis for the pullout test configuration used in Phase Two. In Phase Two, the effect of SMA surface roughness was first investigated by applying sand with varying particle sizes, ranging from 0.6 mm to 1.18 mm, to create different surface textures on the SMA rebars. Two different couplers namely Mechanical Bolted Coupler (MBT) and Full Grout Coupler (FGC) were used to investigate the effect of surface roughness on the performance of bond strength. The experimental pullout test was configured based on the DPT setup method. The results indicated that different coupler types yield different bond strength performances. For the FGC coupler, coarser sand particles resulted in higher bond strength, and vice versa. In contrast, for the MBT coupler, bond strength was reduced by 72% with the introduction of the sand coating. This highlights that, in addition to rebar surface roughness, the type of coupler plays a significant role in determining the bond performance of SMA rebars. In Phase Three, a prediction model for determining the bond strength of mechanical couplers was derived using the experimental data collected from Phase Two through regression analysis. The prediction model is applicable for the steel MBT connections, the sand-coated SMA MBT connections, and the sand-coated SMA FGC connections, where the percentage error of the predicted value was less than 10%.In conclusion, this study highlights that effect of clamp zone did play an important on bond strength, the surface roughness shows significance when FGC coupler for sand-coated SMA reinforcement was utilised,. Finally, the good prediction model with less 10% error for sand-coated SMA connections was developed, which highlights the novelty of this thesis.