A General Equation for the Steel Stress for Bonded Prestressed Concrete Members

I n order to perform an flexural analysis of a bonded prestressed concrete section, it is necessary to consider both the equilibrium of forces acting on the section and the compatibility of the strains. For this analysis, the actual stress-strain curves for the concrete and the steel may be used or alternately certain simplifying assumptions for a more general but less exact solution may be made. Similarly, the maximum strain in the concrete should be based on the strain distribution corresponding to the peak moment (a M/ae, = 0) but may generally be approximated satisfactorily by using a fixed value such as –0.003. It should be realized that at the time when prestressed members are designed, the particular reel or heat of steel that will be used is often unknown so the exact stress-strain curve for the steel cannot be known. It is, therefore, frequently more appropriate to use a simple lower bound approximation for the stress-strain curve rather than more complex procedures which require the exact stress-strain curve for the specific steel.