A Direct Comparison of the Traditional Method and a New Approach in Determining 220 Transfer Lengths in Prestressed Concrete Railroad Ties

Abstract

This paper presents the detailed analysis of surface strain data obtained at six prestressed concrete tie plants in the United States. These data were obtained by the authors by conducting a total of 220 transfer length measurements on prestressed concrete railroad ties with different concrete-mix designs and reinforcement variations. The surface strain profiles of the railroad ties were obtained using the traditional Whittemore gage, as well as a rapid non-contact technology, called laser-speckle imaging (LSI), that was previously developed by the authors. The LSI technique achieved a microstrain resolution comparable to that was obtained using mechanical gauge technology. The measured surface strain profiles were then analyzed by both the 95% AMS (95% Average Maximum Strain) method, and the ZL (Zhao-Lee) method that was recently proposed by the authors. The ZL method is an unbiased statistical method that provides a more accurate and reliable transfer length determination. A direct comparison between the 95% AMS method and the ZL method was achieved by applying both methods to determine the 220 railroad tie transfer length values. The comparison confirmed the bias of the 95% AMS method in estimating transfer length value, as predicated by theoretical analysis.