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

the reinforcement located within the end h/8 of the member experienced significantstress” (p. 74).Based upon this observation, Tuan et al. designed a new end-region reinforcingdetail that concentrated reinforcement near the beam end. Special transversereinforcement (threaded rod or deformed bars welded to top and bottom plates) designedto resist 2% of the applied prestressing force was provided within the end h/8 of themember. An equal amount of reinforcement was spread over the region between h/8 andh/2 from the beam end. In this way, the amount of transverse reinforcement required byAASHTO in the end h/4 was instead spread over the end h/2.Beams reinforced with the proposed detail were reported to have smaller crackwidths and lengths than those using standard details. However, stresses were higher(mean maximum spalling stress of 16 ksi compared to 11 ksi). Four beam end regions hadmaximum stresses that exceeded the AASHTO limit by as much as 30%; all were 43-in.I-beams (instrumented near the flange/web junction, as shown previously in Figure 2.35).IT-beams again experienced lower spalling stresses than did I-beams.Tuan et al. used their strain gage readings to calculate the total transverse-barforce at prestress transfer for each beam end region. As they note, the transverse-bar forceat transfer “is not limited to steel in the end h/4 of the member” (p. 77). Unfortunately,their instrumentation was, in the case of I-beam specimens, and so a substantial amountof extrapolation was sometimes required in the calculation of transverse-bar force attransfer (spalling force).Though the accuracy of their reported total forces is called into question becauseof this extrapolative procedure, some general observations are possible. Beams with0.6-in. strands experienced higher spalling forces (by 20%) compared to similar sectionsprestressed with 0.5-in. strands. The spalling force can be calculated within the end h/456