There is no unique quantity or layout of post-tensioning that provides a satisfactory PT design. This is particularly true with partial prestress design where the emphasis is on strength, deflection and crack control rather than hypothetical service stresses.

Historically, many 2D programs have used allowable service stresses to drive their algorithms for providing a PT solution. This is fast losing favor; some codes have all but abandoned using (hypothetical) service stresses as a design criterion, and other codes (such as ACI 318) are moving in that direction. Some computer generated tendon layouts are not practical for real design.

Whereas you expect a 2D program to help provide a workable tendon design based upon spans, sections and loads, the possible randomness of supports makes this extremely difficult in 3D.

Thus, in RAM Concept , it is necessary for you to define the tendons by generating or drawing them in plan and specifying parameters such as profile and number of strands. For guidance, you should use one of the following for your first estimate:

• your experience
• a preliminary run with Strip Wizard
• a logical guess based upon precompression (P/A) considerations
• a random guess (correctly drawn design strips flag incorrect guesses, and you can use "The Auditor" for help in iterating)

RAM Concept 's PT Optimization feature (see Designing and Optimizing Post-tensioning) automates the search for an economical design and eliminates the need for manual iteration.