Tensile stress limit for prestressed concrete at release: ACI 318-08

The tensile stress limit for prestressed concrete beams at release was evaluated experimentally for seven 54 in. (1370 mm) deep bridge beams. Additionally, an extensive amount of material data was collected through testing and literature review. The purpose of the experimental program was to characterize the mechanical properties of concrete, including the relationship between the inplace strength of a beam and its representative material strength. Beams fabricated as part of this study cracked with an applied stress less than half of the apparent strength determined from material tests. The ACI 318 tensile stress limit was not sufficient to prevent cracking. It was concluded that limiting the extreme fiber tensile stress to 4√f'_ci psi (0.33 √f'_ci MPa) will adequately prevent cracking at release.