Investigation of the application scope of bond strength empirical formulas for various FRP bars in concrete: A case study utilizing the safety probability value with a large test dataset

Empirical formulas play a pivotal role in the assessment of bond strength between Fiber Reinforced Polymer (FRP) bars and concrete. Although some studies have explored the applicability of existing formulas, a comprehensive investigation on a broad scale, encompassing diverse types of FRP bars, and their application in both normal and high-strength/ultra-high-strength concrete, is lacking. This study aims to consider the application scope of seven existing formulas for assessing the bond strength of diverse FRP bars in various concrete types, including normal, high-strength, and ultra-high-strength concrete. The evaluation of formula applicability utilizes a dataset comprising 1019 pull-out test specimens from 34 recent studies. In the dataset, 447 specimens fall within the typical application scope, involving Glass (G) FRP bars with diameters ranging from 8 to 16 mm embedded in normal concrete. The remaining specimens cover broader application scenarios, including the use of high-strength or ultra-high-strength concrete, smaller or larger bar diameters, and the incorporation of other bar types such as Carbon (C) FRP and Basalt (B) FRP. The results highlight variations in the correlation between calculated values and experimental outcomes across different formulas. Appropriate safety coefficients have been applied to all seven formulas, expanding their applicability to a wider design spectrum.