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

Figure 2.47 Required splitting reinforcement for a trapezoidal tub girder(after AASHTO LRFD, 2008, Interim)In summary, since the first mention of prestressed concrete in the AASHO code,the end-region concrete and steel requirements for pretensioned beams have changed aslisted below. The majority of these changes have occurred in the past 15 years.• End blocks were required, then not recommended;• Requirements for confining reinforcement in the bottom flange were introduced,and then further fleshed out;• The allowable stress in end-region reinforcement has gone from 20 ksi to yield,and back down to 20 ksi;• The length of the zone in which the required transverse reinforcement is to beplaced first decreased from d/4 to h/5, and then increased to h/4;• The name given to end-region reinforcement has changed from the generic“vertical stirrups” to “bursting” reinforcement to “splitting” reinforcement; and78