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

4.2.2.3 Beam 1: Transverse-Bar Bursting & Spalling StressesBursting and spalling stresses in transverse reinforcement are shown inFigure 4.3. The circles in this figure represent stress values, and are superimposed onBeam 1 end-region elevations at the location of their associated strain gage. Circle area isproportional to the stress measurement; its color relates the stress measurement to theAASHTO design maximum, 20 ksi. Crack patterns from transfer are also shown on thebeam elevation.Measured stresses were low compared to the AASHTO limit in general.Transverse-bar stresses typically decreased with distance from the beam end, even in thebursting zone. Reasonable correlation can be seen between the presence of a visible crackand the measurement of moderate stresses (at least 8 ksi) or higher. Nevertheless, at somelocations where cracking was noted, stresses were relatively low (e.g. Location 1C,Figure 4.3).For one gage located at the top flange/web junction (Location 1A), stressesexceeded the AASHTO limit (thus is represented by a red dot in Figure 4.3). The highstress was measured adjacent to long, wide cracks (20 to 30 in., 0.020 in.). This crackingwas exacerbated, if not caused, by the large skew. Across the beam width from thislocation (at Location 1D), the prestressing force from the strands was fully transferred tothe section: the provided bond length (90 in.) exceeded the transfer length by a factor ofthree. The cracks at the top flange/web junction extended from the top corner of the endblock (at Location 1A), then to run diagonally across the web.The only other location where the measured transverse-bar stress approached theAASHTO limit was mid-depth at the square end of the beam (Location 1E, Figure 4.3).By 1 hour after transfer, readings from this gage surpassed the 20-ksi limit stress. The155