Civil Engineering Association

ABSTRACT
The first objective of this thesis was to determine the effect of using self-consolidating
concrete versus normal concrete on transfer and development lengths, and flexural strengths of
prestressed members. Three small rectangular members were made, two cast with SCC mixes
and one cast with a conventional mix, to determine the transfer length of each mix. Transfer
lengths of both ends of each member were determined by measuring the concrete surface strains.
The change in the transfer length was monitored by determining the transfer length of each
member at prestress release, 7 days after release, and 28 days after release. All concrete mixes
had lower than code determined transfer lengths at prestress release. Each concrete mix showed between a 12 to 56 percent increase in transfer length after 28 days. One SCC mix exceeded the ACI code stipulated 50 strand diameters 7 days after prestress transfer. The other SCC mix was consistently below the transfer length of the conventional concrete.
Separate development length members were cast in a stay-in-place steel form used for
creating structural double tees. Each development length member was a stub tee. Iterative load
testing was performed to determine the development length of each SCC and conventional mix.
Development lengths for both SCC mixes were approximately 20 percent shorter than ACI and
AASHTO code predictions. A development length for the conventional concrete was not
determined due to non-repeating test data. The flexural strength of each member was determined during load testing. All concrete mixes achieved higher than the ACI predicted strengths.
The second objective of this thesis was to experimentally measure prestress losses and
compare these experimental values to theoretical models. Crack initiation and crack reopening
tests were performed to experimentally determine the prestress losses in each member. Three
theoretical models were evaluated, the sixth edition PCI Design Handbook suggested model, a
1975 PCI Committee on Prestress Losses model, and the AASHTO LRFD prestress loss model.
The crack initiation experimental values tended to be between 10 and 15 percent lower than
theoretical models. In general, the crack reopening prediction of the effective prestress had a good correlation with theoretical models.


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