Modification of ACI Code Equation for Stress in Bonded Prestressed Reinforcement at Flexural Ultimate

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Title: Modification of ACI Code Equation for Stress in Bonded Prestressed Reinforcement at Flexural Ultimate

Author(s): Alan H. Mattock

Publication: Journal Proceedings

Volume: 81

Issue: 4

Appears on pages(s): 331-339

Keywords: bond stress; bonding; building codes; compressive strength; prestressed concrete; prestressing steels; reinforcing steels; standards; stresses.

Date: 7/1/1984

Abstract:
Eq. (18-3) of ACI 318-77 is an approximate equation for f(ps), the stress in bonded prestressed reinforcement at nominal moment strength. It was orginally proposed by joint ACI-ASCE Committee 423 in 1958 in "Tentitive Reccommendations for Prestressed Concrete". A study was made of the influence on the accuracy of Eq. (I8-3) (a) prestressing steel for which f(py) = 0.9Of(pu), (b) high-strength concrete, (b) additional unprestressed flexural tension reinforcement, (d) compression reinforcement, and (e) use of a slender T-ztion beam rather than a rectangular section beam. A modified version of Eq. (18-3) was developed that takes into account the above factors and yields values of fps in closer agreement with values obtained from an analysis based on simultaneous satisfaction of compatibility of strains and equilibrium of forces. This modified version of Eq. (M-3) has been included in ACI 318-83.