As Mark said, post-tensioned piles are unusual (but
pretensioned piles are common).
The procedure for calculating a post-tensioned pile
interaction diagram is:
the strains and stresses in the concrete, tendon and
rebar before grouting:
A. Tendon force (and strain) is known from stressing info
B. Cross section strains are
determined from P/EcAt, where P is tendon force and At is transformed area of
concrete and rebar (assumes tendon at centroid).
C. Determine concrete and rebar stresses from
cross section strains.
A. Remember net forces and moments of PT,
concrete and rebar are zero at this time.
B. All strain changes from here on affect PT,
concrete and rebar
incremental cross-section strains and
calc cross section forces:
A. From the incremental strains, determine the
total strain in each component
B. From the total strain in each component,
calculate its stress and force.
C. Sum the forces to get total section forces and
moments for pile
4. Repeat #3 as
necessary to get enough data for a good curve.
If the pile is
pretensioned, the calculations in #1 are a little more complicated (need to
solve two simultaneous equations), but it is still fairly
Structural Concrete Software,