Ecentricity limits and tendon profile
Eccentricity Limits and Tendon Profile
Since the moments change along the length of a beam, we must change some aspect of the prestress also. The only remaining variable is the eccentricity.
Tension on Top at Transfer
We determine an expression for the eccentricity in terms of the other knowns:
Hence we have a lower limit for the eccentricity as:
Tension on the Bottom in Service
Hence we have an upper limit for the eccentricity as:
Since the upper and lower kerns (the Zt/A and Zb/A quantities) are constant for constant geometry, and since P is also constant, it can be seen that the cable limits follow the same profile as the bending moment diagrams at transfer and in service.