When reviewing the load on a gaped support, there is a load in the same direction as a large gap. The pipe never closes the gap, so why is there a load on the support in that direction?
If you are running a non-linear analysis, 9 times out of 10 the answer is due 1 of 3 reasons: Nonlinear analysis, Friction, or Dynamic analysis rules.
1. Nonlinear analysis
Problem is directly with Load sequencing (see WIKI here). Essentially do not consider individual load cases results (ex. Gr, T1, W1, E1, etc..), only consider the operating conditions (GrT1P1, GrE1, GrT1W1, etc...). Only consider the individual load case when trying to understand Why the results of an operating condition are what they are.
2. Friction
Another reason for forces in gapped direction would be directly attributed to Friction. Perform the following test: for each support in question change the Friction to 0.00 for no friction. Now re-run the analysis and check the results. The force should now be removed in the gapped direction. Why you ask? because one or more gaps may have closed. Example: guide support with the following gap settings:
Stiffness = RigidGap Up = 100Gap Down = 0.00Gap Left and Right = 0.1Friction = 0.3
Look at the Support output report for all operating condition (ex. GrT1P1E1)
Force: fx = 944 (axial), fy = 250 (up), fz = 2181 (left)
Movement in local coordinate: dx = 1.63 (axial), dy = 0.94 (up), dz = 0.1 (left)
Because the left gap on the support closed there is a friction force as the pipe is moving up. However, when performing the test above, there is no friction and thus free to move up therefore force in the up direction would then be 0.00 as expected.
3. Dynamic analysis rules
Remember that all dynamic analysis depend on Modal Analysis results and are subject to the rules of performing a Modal Analysis.
Note: if using a guide support where 2 opposite directions have large gap settings. Highly suggest to model using an Incline support instead of a Guide support.
"Support" sub report using Results> Output Report in AutoPIPE
Bentley AutoPIPE