Experimental evaluation of the transfer and development length of 28.6 mm diameter grade 1780 strands in normal strength concrete

Abstract

This research experimentally addresses the determination of the required transfer and development length of beams reinforced with 19-wire 28.6 mm diameter, grade 1780, prestressing steel strands, which contain 5.4 times more area than typical 13 mm diameter strands. Eight (8) full-scale beam specimens were constructed to evaluate the influence of different concrete compressive strengths on transfer and development length of these large-diameter strands with the overarching goal of determining whether they could be used in precast concrete applications. Demountable Mechanical (DEMEC) gauges were used to gather surface strain readings, which were further analyzed using the 95 % of the Average Maximum Strain (AMS) method to obtain the transfer lengths. Development length testing was performed by loading the beams until failure at locations between the theoretical development length and the experimental transfer length to obtain the experimental development length values. The tests conducted in this research suggest that beams reinforced with these strands would have transfer lengths between 22 and 52 strand diameters, and development lengths would likely be in the range of 60–120 strand diameters for concrete strengths between 45 and 65 MPa.