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

No citation is provided in the PCI Design Handbook for the de facto increase inallowable stress for the transverse reinforcement. Writing in the PCI Journal five yearsafter the PCI provision was adopted, Tuan et al. (2004) state that “additional experimentsare needed to investigate the possibility of reducing the splitting reinforcement withincreased stress limit to 30 ksi or even 36 ksi” (p. 81), suggesting that sufficientexperimental justification for a 30-ksi design stress for transverse reinforcement did notexist at the time that this design provision was adopted.2.6.5 CEB-FIP RecommendationsThe CEB-FIP Model Code (1990) advocates the use of STM for the design ofprestressed concrete beam end regions. However, the code contains alternativeprocedures based on linear analysis, to be used “should the use of the strut-and-tie modelbe too problematic because of the complexity of the stress field” or “if the strut-and-tiemodel is not applicable due to lack of transverse reinforcement” (Clause 6.9.12.1).In the linear analysis procedures, end-region transverse forces are calculated usingprism models: a symmetrical prism after Guyon (1955) for bursting and an equivalentprism similar to Gergely and Sozen (1967) for spalling. Gradual transfer of prestress tothe section is accounted for in the prism length equation. Splitting force is not calculated,but rather handled by prescriptive cover and strand-spacing requirements (>3 ).Standard U.S. practice (0.5- or 0.6-in. strands at 2 in. centers) complies with thesesplitting requirements.2.7 DOT STANDARDS FOR U-BEAMSPretensioned concrete U-beams exist as standard sections in four states: Texas,Florida, Colorado and Washington. The four states’ design standards are compared,82