The stress f,, in the prestressing steel at ultimate moment capacity of partially prestressed concrete beams is investigated both experimentally and through the use of a computerized nonlinear analysis. An extensive parametric evaluation is undertaken. It clarifies the effects on fps of various parameters such as the type of section, the reinforcing index, the partial prestressing ratio, concrete strength, prestressing and reinforcing steel grades and different amount of compression reinforcement. Sensitivity of fp, to the variation of certain parameters is also studied. The results of the nonlinear analysis are compared with the ACI 318-83 equation, other proposed equations and experimental results. Some recommendations are derived and a modified equation to predict f„s is proposed. Application of the proposed method is illustrated with the aid of a numerical example.
