Short-Term Partial-Interaction Behavior of RC Beams with Prestressed FRP and Steel

The deformation of a prestressed concrete (PC) member is controlled by the variation in flexural rigidity (EI) both along the length of the member and with applied loads. Typically, the moment-curvature M/χ approach is used to quantify EI with the analysis being mechanically correct prior to cracking as the only empirically derived components are the material stress-strain relationships. Postcracking, however, the M/χ approach has to be semi-empirical as it cannot directly simulate the effects of tension stiffening. This paper presents a displacement-based M/Θ approach for determining the behavior of PC members, with and without supplementary tension reinforcement. Applying the mechanics of partial-interaction (PI) theory, the approach directly simulates the formation and widening of cracks as the reinforcement pulls from the crack face, thus directly allowing for tension stiffening. The PI M/Θ approach can quantify the equivalent flexural rigidities (EIequ) associated with tension-stiffening which can be used in standard analysis techniques to predict member behavior. The proposed PI M/Θ is finally used to predict the behavior of members with both steel and fiber-reinforced polymer (FRP) reinforcement and a good correlation with test results from serviceability to ultimate loading is obtained.