Acceptance Criteria for Bond Quality of Strand for Pretensioned Prestressed Concrete Applications

In this test program, 6 samples of 0.5 in. (13 mm) diameter strand were obtained from precast, prestressed concrete producers from widely separated regions of North America to evaluate strand bond performance. A total of 216 tests were carried out on the specimens, including pull-out tests, end slip at prestress release and at 21 days, as well as development length tests. The pull-out test proved to be an accurate predictor of the general transfer and development characteristics of the strand in pretensioned, prestressed concrete applications. Based on the test results, the following major findings can be drawn: 1) the transfer and development lengths of strands with average pull-out capacity exceeding 36 kips (160 kN) were considerably shorter than predicted by the ACI transfer and development length equations; 2) strands with average pull-out capacity less than 12 kips (53.3 kN) were unable to meet the ACI transfer length criteria, and failed prematurely in bond at the ACI development length, without noticeable warning deflection.