Doctoral Dissertations

Date of Award

5-1991

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Civil Engineering

Major Professor

Edwin G. Burdette

Committee Members

J. Harold Deatherage, David W. Goodpasture, Jack Wasserman

Abstract

In an attempt to resolve the controversy over the adequacy of the ACI 318-83 Building Code Requirements on development length of prestressing strands, a major experimental research on bond development of seven-wire prestresssing strands was conducted. Twenty-two full-scale AASHTO Type-I prestressed concrete bridge beams were tested for transfer length and strand end slip at transfer and for development length in static destructive tests. Additionally, transfer length in prestressed concrete prisms and pullout behavior of non-prestressed strands in concrete prisms were obtained. A comprehensive review of related research is presented. 1/2" Regular, 1/2" Special, 9/16" and 6/10" strands were tested. Other variables included strand surface conditions (milled, weathered, and grit-impregnated epoxy-coated), concrete strength, strand pretension level, strand spacing, and strand manufacturers. Transfer length was determined from strain measurements on concrete surface using a newly developed Slope-Intercept method. Measured transfer lengths for milled surface strands were proportional to strand diameters except the 6/10" strand which had shorter transfer length. The mean transfer lengths compared closely with the ACI code requirements. Transfer length was found to be well correlated with end slip at transfer and directly related to the strand pretension level. Flexural bond strength was deduced from the load tests of beams that exhibited bond failure. The flexural bond strength was found to be proportional to strand diameter for all the strands. The mean flexural bond length for milled surface strands was 42% more conservative than the code requirements. Smaller strand spacing of 1.75" for the 1/2" Regular strands did not appear to cause any adverse effects on the transfer length or the flexural bond length, indicating that the code requirement for strand spacing of 4 times the strand diameter is satisfactory. Weathered strand surface condition improved transfer length more significantly than flexural bond length. 1/2" Regular epoxy-coated strands with grit-impregnation performed considerably better than the 1/2" Regular milled strands. Concrete strength did not affect the transfer and flexural bond lengths of smaller strands but did significantly affect the larger 6/10" strands. There were nominal effects on the transfer and flexural bond lengths of the strands from different manufacturers. The interrelation of development length with beam behavior was studied. Load capacity of beams that cracked in web-shear appeared to be governed by the available development length from the shear-crack at the face of support. Flexural-shear crack was observed to be a critical section for development length requirement evaluation.

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