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

effects) were examined. Several factors contributing to measurements of high transversebarbursting or spalling stresses were identified. Lastly recommendations were made withregard to U-beam end-region reinforcement and bursting design in special cases(debonding and dapped ends).5.2 CONCLUSIONSFrom the experimental and analytical studies conducted for TxDOT ResearchProject 5831, the following conclusions can be made:1. Though most strain gages on end-region reinforcing bars indicated low bursting andspalling stresses (less than about 5 ksi), some returned much higher readings.Experimentally determined stresses in both the bursting zone (Beam 2) and spallingzones (Beams 1 and 2) surpassed the limit set by AASHTO LRFD (20 ksi) by asmuch as 50%. The high bursting and spalling stresses provide a basis for proposeddesign changes in the end-region details.2. Contributing to the high maximum transverse-bar stresses at prestress transfer (basedon database analysis) were two factors applicable to the U-beam specimens tested:high average transverse-bar bursting/spalling stress in the end region and highbottom-fiber stress near the beam end.3. Placed in context of U-beam design standards of other state DOTs, Texas U-beamshave little transverse reinforcement in their webs. Much transverse reinforcement,however, is provided within the end blocks, especially near the center of the section.4. The provision of additional transverse reinforcement in U-beam webs isrecommended. This reinforcement may take the form of new bars near the interiorweb face and bundled bars near the exterior, to extend to a distance of at least 36 in.from the beam end. Proposed changes to the end-region reinforcing details will be189