An analysis of the methodologies utilized in determining the transfer length of prestressed concrete members

This study was prompted by the inconsistencies evident in the current methods that are used to determine transfer length. The goal of this study was to quantitatively define some of the many variables that affect transfer length measurement. The variables that were investigated in this study are gage length, gage spacing, strain gage sensitivity, strand spacing, shear lag, beam weight, transfer bond stress, data smoothing, and the data measurement process. Of these variables, only one could not be quantitatively defined; shear lag. However, the effects of gage length, gage spacing, and data smoothing were well defined, and a new method, the "Variable % Strain Method", is based on the mathematical quantifications of these variables.

The existing "slope-intercept" and "% average maximum strain" (especially the "95% Average Maximum Strain Method") methods were analyzed extensively, and their respective strengths and weaknesses were quantified and illustrated. In general, the "% strain" methods were found to be more reliable. However, a theoretically correct "error adjustment" factor was derived for the "slope-intercept" methods, and it is an integral part of the new Corner Point Method. Overall, the "Variable % Strain Method'' was determined to be the best and most reliable of all methods examined. Yet, in order to increase transfer length measurement accuracy and precision, additional research needs to be conducted in order to quantitatively define shear lag, and also to define the exact nature of the transfer bond stress profile.