Why are the displacement results so different for a single load case (ex. T1) when a single support has been added to the piping in AutoPIPE?
Example:
Model #1, no support, the thermal movement at A05 is :
Notice the thermal movement at A01 - A05 is exactly the same.
Now, add a support to A02, Vstop with gap above, now the results from T1 are significant different with the new support but still no restraint above to prevent movement of the pipe up.
Can please explain why?
In order to consider Gap / Friction / Soil properties in a model it must be analyzed using a Non-linear Analysis. This type of analysis uses load sequencing. The load sequence always starts with the Gravity load case (GR) being applied first. After the model has been displaced per the gravity (GR) load case, based on piping arrangement and restraints, the next load case defined in the sequence (ex. T1) is applied to the already distorted piping. Again, after the model has been displaced by the 2nd load case (ex. T1), then next load case in the defined sequence is applied (ex., P1), and continues until all load cases defined in the sequence have been applied to the model.
When reviewing results it is always best to review the operating conditions (ex. Grt1, GrT1P1, etc.. ) and not the individual load case (Gr, T1, P1). The individual load cases should only be considered when trying to understand the major contributors to a given operating condition.
With regards to the example above, in the segment with no support, there are no non-linear elements and thus the results for that segment should not be any different from a linear analysis, and the principle of super position can be applied.
In this particular example, the initial state for analyzing T1 is GR. Owing to the configuration of this model, when the thermal load is applied there is a pivoting effect of the model at node A02 where the V-stop is applied. For the support to lift off from A02 under T1, it will need to overcome the load applied at A02 due to gravity. As the thermal loading is not enough to counter the effects of gravity, it instead pivots about the V-stop at A02. So the profile that is being displayed for T1 is a correct representation of the change or delta that T1 can cause to the model, when the initial state is gravity. This displacement profile is plotted against the un-deformed shape of the pipe, which may cause the confusion in understanding the results.
Again, results for intermediate load cases in a load sequence like T1 may be a good tool to understand the contribution of a certain load case, however, the results of a single load case other than gravity (like T1, which is a change or a delta caused by T1 to the state of the model set by GR) on its own may not be apparently meaningful and can cause confusion.
"Displacement" sub report
Bentley AutoPIPE