Bursting and Spalling in Pretensioned U-Beams - Ferguson ...

The prestressing force for Beam 1 was measured by three methods (Table 4.1)with good correlation between the various measurements. The value of prestressing forceused for subsequent calculations represents the mean of the measured values frommethods (a) and (b), ram pressure and strand elongation, and was within 1% of the targetvalue (Table 4.2).Table 4.1 Beam 1 as-measured prestressMethod Prestress (ksi) Deviation from (a)(a) Ram Pressure 196.9 —(b) Strand Elongation 205.5 + 4.4%(c) Strain in Strands 190.8 - 3.1%Table 4.2 Beam 1 applied prestressing force compared with target valueMethod Prestress (ksi) Prestressing Force (kip)Average of (a) and (b) 201.2 2401Target 202.5 2417The compressive strength of the cylinders match-cured to the release point was6.4 ksi, or very nearly the target release strength (6.3 ksi). The bottom-fiber stress attransfer was 0.63 .Cracking occurred in the beam end regions (horizontal and diagonal cracks) andalong the top edge of the beam (vertical cracks), immediately after prestress transfer.End-region cracks were typically hairline, with widths of 0.005 in. or less except at onelocation near the top flange/web junction at the skewed end (Location 1A in Figure 4.3).151