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How are creep, shrinkage, and secondary prestress effects extracted from staged-construction results?

Answer: For statically indeterminate structures, the contribution from individual sources of tendon loss may not be obtained because of the interrelationship among loss components. For example, shrinkage strains may cause stresses which affect creep behavior, therefore their individual contributions may not be separated unless the shrinkage effect on creep is neglected.

For statically determinate structures, creep, shrinkage, and secondary prestress effects may be estimated through post-processing. For example, response may be evaluated both with and without creep consideration, then creep behavior may be estimated from the difference between these results.

A procedure available to both statically determinate and indeterminate structures is as follows:

1. Replace the original staged-construction load case with a sequence of chained staged-construction load cases, as described in the Obtain results for individual stages of a staged-construction load case tutorial.
2. For each effect to be extracted, create a separate load case. Examples include load-application, post-tensioning, creep, and shrinkage effects.
3. Create a load combination to extract the desired forces which result from a single type of loading.

To demonstrate this procedure, assume there is a single staged-construction load case with the following stages:

• Stage 1 – Erect the first set of segments and apply self-weight (duration = 0 days)
• Stage 2 – Apply post-tensioning (duration = 0 days)
• Stage 3 – Create an empty stage in which creep and shrinkage take effect (duration = 7 days)
• Stage 4 – Erect the second set of segments and apply self-weight (duration = 0 days)
• Stage 5 – Apply post-tensioning (duration = 0 days)
• Stage 6 – Create an empty stage in which creep and shrinkage take effect (duration = 7 days)

Replace this set of stages with a chained sequence of six load cases, listed as follows:

• LC1
• LC2
• LC3
• LC4
• LC5
• LC6

To obtain only post-tensioning forces, create the load combination which follows:

• PT-Only = LC2 - LC1 + LC5 - LC4

Similarly, to obtain only creep and shrinkage forces:

• Creep-And-Shrinkage = LC3 - LC2 + LC6 - LC5

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See Extracting creep, shrinkage, secondary prestress effects and other load effects from staged-construction results

How is design done for the individual stages of a staged-construction load case?

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