huangyhg

post-tensioning design (adapt procedure)
am currently preparing a spreadsheet based program for post tensioned slab design based on effective force approach (wherein no computation of prestress loss is carried out)and the program outputs only the pt forces:
to arrive at an optimized force in each span we carry out the following procedure:
1) assume a maximum drape for each span and determine a minimum force which satisfies the maximum allowable tensile stresses.
2) use the same force for every span
3)adjust the force to meet the following requirements specified by the user:
minimum percentage of dead load to balance for each span
minimum average pre-compression for every span
maximum spacing of the tendons.
4)after these initial adjustments, each span is checked for compliance with the following:
5) maximum percentage of dead load to balance: if the balanced loading in any span exceeds the maximum percentage specified by the user, the program adjusts the tendon drape in the span in order to lower the balanced loading.
6) average pre-compression and maximum stresses: if either the average pre-compression or compressive stresses exceed the permissible values the program would stop and display a message box so that the user revises its design bounds listed above.
similar was the procedure listed in adapt manual too.however, my question is:
a)the post tensioning force in step 1 is calculated by taking the maximum tensile stress out of all the spans.this value of the post tensioned force obtained is used for all the spans.now,
would'nt this result in an overconservative value for a span wherein the tensile stress is very less ?

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