Resistance Factors
In the 2006 LRFD Interims, Art. 5.5.4.2 now requires the concrete sections to be classified as Tension Controlled, In Transition, or Compression Controlled. Precast/Prestressed Girder uses the criteria outlined in article and commentary 5.5.4.2.1 to determine this, and then applies f factors as per Art. 5.7.3.2. Precast/Prestressed Girder first determines the layer of strand or rebar closest to tension face. Distance from extreme compression fiber to this layer of steel closest to the extreme tension face is defined as dt. The program then computes the distance to neutral axis, c, for the applied moment from extreme compressive force and then determines c/dt value. It then compares these c/dt values with those in the figures shown below (reference Figure 5.5.4.2.1-1) and determines the phi (φ) factors according to the classification.
If the section is classified as an In Transition section, Precast/Prestressed Girder calculates an interpolated value based on a linear variation of f with c/dt.