Development Length of 0.6-Inch Prestressing Strand in Standard I-Shaped Pretensioned Concrete Beams

The use of 0.6 in prestressing strand at a center-to-center spacing of 2 in allows for the optimal implementation of High Strength Concrete (HSC) in precast, prestressed concrete bridge superstructures. For this strand configuration, partial debonding of strands is a desirable alternative to the traditional method of draping to alleviate extreme concrete stresses after prestress release. Experimental evidence suggests that existing code provisions addressing the anchorage of pretensioned strands do not adequately describe their behavior. In addition, the anchorage behavior of partially debonded strands is not fully understood.

Results are reported from a research study conducted to determine the anchorage behavior of 0.6 in strands at 2 in spacing in fullsize, plant-cast AASHTO Type I I-beams. Concrete strengths ranged up to 15,000 psi. Strand featured either a bright mill finish or a rusted surface condition. A variety of strand debonding configurations were investigated. The use of pull-out capacities and strand draw-in measurements to predict the anchorage behavior of prestressing strands was also examined.

Along with recommended design procedures for anchorage of prestressing strand, a review of the evolution and shortcomings of existing code provisions is presented. The use of this strand configuration is concluded to be safe, and partial debonding of prestressing strands is shown to be an effective means of reducing stresses in the end regions of pretensioned beams.