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

spalling stresses were measured in transverse reinforcing bars within the end regions ofpretensioned concrete beams.4.3.1 Studies of Bursting & SpallingPast studies included in the transverse-bar bursting and spalling stress database,previously discussed in Section 2.4.2, are listed in Table 4.5.Table 4.5 Specimens examined in past studies of bursting and/or spalling stressesSource Year End-Region Type Number of Strain-Gage LinesMarshall & Mattock 1962 14 I-beams SingleItani & Galbraith 1986 3 I-beams Multiple (3 or 4)Tuan et al. * 2004 18 I- and 8 IT-beams SingleCrispino 2007 2 I-beams Multiple (4)O’Callaghan 2007 8 I-beams Multiple (3 or 4)* For additional information on the layout of transverse reinforcement in thesespecimens, Tadros, Yehia and Jongpitaksseel (2003) was consulted.While all these studies investigated stresses in transverse reinforcement at transferof prestress, they did so by slightly different methods. Notable among the methodologicaldifferences is the number of distinct strain-gage lines (along the beam length) used withinthe end region. In the case of beam end regions instrumented with all their strain gages ina single line, in order for the maximum transverse stress to be measured, a researcherwould need to know a priori the maximum-width crack locations in a pretensioned beamspecimen. When the inherent randomness of cracking in concrete is considered, itbecomes clear that the use of multiple lines of strain gages is more likely to yield highermeasurements of stress. The additional gages do not induce high stresses, but rather allowfor their measurement.168