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

treatment (counting the transverse reinforcement near the center of the end block) iswithin the intent of the AASHTO LRFD is discussed further in Section 2.7.5.2.7.2 Florida U-BeamAdapted from the Texas standard, the U-beam has existed as a standard section inFlorida since the mid-1990s. At present four depths have been standardized (rangingfrom 48 to 72 in), including a 54-in. section identical in cross section to the Texas U54(show previously in Figure 2.49). Up to three rows of 26 strands can be placed in thebottom flange.End-region transverse reinforcement within the webs of the Florida U-beam ismore substantial than that in the Texas U-beam, with one #5 bar in each web at 3 in.spacing. The larger bar size and the closer spacing combine for an 85% increase fortransverse web-reinforcement in the beam end region compared with the Texas standard.Transverse reinforcement within the void-projected area of the end block issimilar to the Texas U-beam (Figure 2.53), with three layers of transverse bars: one eachat the outer (6 – #5) and inner faces (6 – #4) of the end block, and one between (6 – #5).A recent Florida DOT design bulletin sets limits on the bonded prestressing forceat pretensioned beam ends in order to control end-region cracking: the limits for U-beamswere set such that the transverse-bar design stress is 18 ksi (Nickas, 2004). This designstress is 10% less than that prescribed by AASHTO.At skewed ends, the end blocks used in Florida U-beams are always skewed (likeFigure 2.51-b), never triangular (Figure 2.51-a). The maximum allowable skew is muchless than allowed in Texas: 15° vs. 45°. End blocks are 18 in. thick, regardless of thebeam skew.88