The purpose of this research is to establish mathematical models that predicts the bond strength of a reinforcement wire in prestressed concrete members, given the known geometrical features of the wire. A total of nineteen geometrical features of the reinforcement wire were measured and extracted by a precision non-contact profilometer. With these mathematical models, prestressing reinforcement wires can now be analyzed for their bond strength without destructive testing. These mathematical models, based upon a large collection of empirical data via prestressing reinforcement wires from various wire manufacturers in US and Europe, have the potential to serve as quality assessment tools in reinforcement wire and prestressed concrete member production. Most of these models are very simple and easy to implement in practice, which could provide insight into which reinforcement wires provide the greatest bond strength and which combinations of geometrical features of the reinforcement wire are responsible for providing the bond strength.
Our various empirical models have shown that the indent side-wall angle, which is suggested by the ASTM-A881/A881M, may not be the only significant geometrical feature correlated to the transfer length and bond strengths. On the contrary, features such as the indent surface area, indent width, indent edge surface area, indent volume, and release strengths do have significant correlations with the ultimate transfer lengths of the prestressed concrete members. Extensive experiments and testing performed at the Structures Laboratory in Kansas State University, as well as field tests at Transportation Technology Center, Inc. (TTCI) and one Prestressed Concrete Railroad Tie manufacturing facility, have been used to confirm the model predictions.
In addition, our experimental results suggest that the maximum pull out force in the un-tensioned pullout testing has significant correlation with the ultimate transfer length. This finding could provide reinforcement wire manufactures with a quality assurance tool for testing their wires prior to the production.
The resultant mathematical model relating the wire geometrical features to transfer length is referred to as the Bond Index Number (BIN). The BIN is shown to provide a numerical measure of the bond strength of prestressing steel reinforcement wire, without the need for performing destructive tests with the reinforcement wire. We believe that with the BIN and the maximal pull-out forces from the un-tensioned pull-out tests, one can have better insight into the optimal reinforcement wire design by testing the performance of wires before they are put into production lines.