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

4.3.7 Concluding Remarks on Database AnalysisAs mentioned previously, for the majority of beam end regions studied (40 of 57),spalling behavior was examined without adequate instrumentation to assess burstingbehavior. Discussion above focused on the LRFD end region (the end h/4 of a beam),rather than distances further into the beam in which bursting stresses reach theirmaximum. That the transverse-reinforcement design procedure stipulated in AASHTOLRFD tends to keep maximum bursting and spalling stresses below 20 ksi should not beinterpreted as an indication that the AASHTO-provided reinforcement is all that isrequired for good end-region behavior. Crispino (2007) and O’Callaghan (2007) haveboth identified the need for reinforcement outside the h/4 region in bulb tees: the formerdue to spalling behavior, and the latter due to bursting behavior. Unfortunately, at thistime, too few studies have examined transverse-bar stresses sufficiently further into thebeam to provide for a reasonable meta-analysis of bursting behavior.Lastly, it should be noted that the assumption of a 20-ksi average stress fortransverse reinforcement is inappropriate if a single instance of a transverse-bar stressexceeding 20 ksi is intolerable for crack-control reasons. If, however, the 20-ksi limit wasset primarily in consideration of average reinforcement stresses and average crack widths,then exceeding the stress limit in limited circumstances (e.g. for one bar in a highlystressed end region) may be considered acceptable performance by some engineers.4.4 RECOMMENDATIONSBased on the experimental results for the two U-beam specimens viewed in lightof the literature, recommendations for the U-beam bursting and spalling reinforcementare made in this section.181