Serviceability check of pretensioned concrete members reinforced with 2,400 Mpa high strength prestressing strnads

In recent years, high strength 7-wire strands that have a 2,400 MPa tensile strength were developed, for which the serviceability check specified in ACI318-14 and KCI 2012 need to be reviewed. The current design codes (KCI 2012 or ACI318-14) permitted that the tensile stress of reinforcing bars at service loads can be assumed as two-thirds of their yield strengths. However, they restricted the net tensile stress of the prestressing strands in Class C prestressed concrete (PSC) members at service loads (∆f_ps) to be less than 250 MPa regardless of the tensile strengths of prestressing strands. Therefore, in this study, a parametric analysis was conducted on the PSC members reinforced with 2,400 MPa high strength prestressing strands considering the key influential factors on the ∆f_ps, such as shape and size of section, partial prestressing ratio (PPR), reinforcing index (w), and magnitude of effective prestress (f_se). The analysis results showed that the ∆f_ps is not affected by section size, and decreases in accordance with increasing f_se, PPR, and cracking moment to service moment ratio (M_cr/M_service). Based on the analysis results, a simple design table was suggested to check if the ∆f_ps satisfies its limitation at the design stages, which does not require any complex iterative calculations for checking ∆f_ps.