During animation of AutoPIPE's displacements load cases, maximum displacement appears larger at a location between existing node points, can pipe displacement values be larger than existing node point values?
From AutoPIPE help for displacement report:
In a linear static load case, each represents the linear force displacement response of a point due to the loads deformed for that case alone. However, a nonlinear static load case represents the force-displacement response of a point due to the loads deformed for that case alone, and considering that the points' initial global coordinate position (prior to application of load) is the deflected position of the preceding (initial state) load case.
Therefore Linear and Non-liner analysis reported displacements are only calculated at node points in the model. No results are given for intermediate locations between existing node points during a Static analysis. The deformed shape of the pipe would be graphically approximated between node points based on influences of applied loads at node points or piping displacement beyond adjacent node points. Many question how many node points are required to achieve high accuracy of displacement. Yes by adding more node point the closer to actual displaced shape will be displayed / calculated. However, adding to many unnecessary node points would significantly increase the analysis time and would not greatly increase the accuracy of the results. See example below.
Example, see image below of pipe between 2 anchors:
Seg A has no node points between the anchors
Seg B has 1 node point between the anchors
Seg C has 2 node points between the anchors
Seg D has 50 node points between the anchors
Displacement due to static Gravity load-case:
Note that Seg A does not have any displacement in between the anchor points. Recall from above, reason being that there was no node point for which the program to apply the load-case nor influence of pipe displacement beyond adjacent node points. Also note the support load reactions for each segment are identical to one another.
Front view, notice that the shape of the displaced curve is smoother as the number of node points increase, but the amount of accuracy is minimal at best.
- Static analysis, no results are generated for piping between node points.
- "Non-Code" combination deflected shape plots would be graphically approximated between node points based on applied loads at existing nodes and influences of piping displacement beyond adjacent node points.
- Adding more node points between existing unsupported nodes does increase the displacement accuracy. However adding too many nodes into the model significantly increases analysis time without much gain in precision. Suggest to use an iterative approach of adding a few additional nodes between supports / existing node points, run a Static analysis, create an Displacement output report (Run1), add more node points into the model, again run a Static analysis, create an Displacement output report (Run 2) and compare the results. If significant difference, repeat iteration of adding more node points as needed until the difference was within an acceptable tolerance.
"Displacement" sub report
Bentley AutoPIPE