Supports settlement - problem with calculation results, FROM: ASECon

Question:

Hallo,

while prepering grid model of composit element (steel-concrete) our customer occured problem with consideration of temporary supports settlement in constructional state. This viaduct has span constuction with temporary supports set in the middle of the range of the spans. 

Temporary supports were modeled as short singular rods connected with girders (they used releases on ends of rodes, rodes carry only vertical forces) and ended it on the other site with "rigid anchorage". Settlements of temporary supports were modeled in the following way (Load-Static Load-Specified Displacement of Supports): they entered value of the displacement in z direction and marked nodes with rigid anchorages of temporary supports. This load was pinned to Load Group: "Settlement of temporary supports (Osiadanie podpór tymczasowych)".

In CS2 construction of girders, temporary supports, rigid anchorages and realeses were activated. 
In CS3 they set load of wet concrete in spans.
In CS4 they set load Group: Settlement of temporary supports (Osiadanie podpór tymczasowych).
In CS5 composit cross-section in spans were activated.
In CS6 temporary supports, rigid anchorages and load group: "Settlement of temporary supports (Osiadanie podpór tymczasowych)" were disabled.

In the following stages composit cross-section under supports was activated, load of equipment. The model includes rheology.

In described constructional states there are no problem with calculation results. First problem wth calculation results occures in Post CS. Program sests loads in Post CS (moving loads, wind load, temperature load) to model which takes into account temporary supports ( temporary supports were disabled in CS6 so all left loads in Post CS should be set  to the construction supported only on permanent supports). 

If they modify model without activating and disactivating load Group: "Settlement of temporary supports (Osiadanie podpór tymczasowych)" in construction states, and at the same time activating and disactivating of temporary supports, rigid anchorages and realeses then calculations in Post CS are made corectly. (program doesn't see in Post CS temporary supports and construction is supportted only on permanent supports).

Could You please explain this situation?

Could You also describe the difference in modeling supports settlement by Static Loads-Specified Displacement of Supports and Sattlement-Sattlement Group-Sattlement Load Cases?
In the second method when makeing settlement group of permanent supports (5 permanent supports), during creating of an envelope of internal forces in composite girders, will program choose the right combinations of settlements for particular permanent supports (for example choosing settlement only for supports 1-3-5 while supports 2-4 would not settle). 

In the attachment I send the model. Could You please help us answer this questions?

Best regards,


Answer:

Hello,

I don't think there is any issue due to this specified displacement in PostCS.  Kindly share image of the problem for better understanding.  From what I checked, the results seem fine even for PostCS cases.


Specified displacement and settlement analysis would essentially be the same thing.  But ease in using settlement analysis is that it takes care of multiple scenarios of settlement by defining just one case.  So, we can simply define settlement value for all 5 supports and define just 1 settlement case with min 1 support settling and max 4 support settling.  This would take care of all the permutations and combinations of settlement that can happen.
Obviously, the case of 1-3-5 settling and 2-4 not settling would be covered by this method.
Hope this helps.  Kindly let us know if further assistance would be required.

Regards,
Nandeep
Technical Manager, MIDAS
Creation date: 10/17/2018 9:40 PM      Updated: 10/18/2018 7:10 AM
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