Applies To Product(s): AutoPIPE, Version(s): 2004, XM, & V8i Environment: N/A Area: Error Subarea: Original Author: Bentley Technical Support Group Problem: AutoPIPE: E801-1: Unstable System When running an anlysis the following occurs: --------------------------- Error --------------------------- E801-1: FATAL ERROR : Unstable system. Need support at node XXX Dir XX --------------------------- OK --------------------------- Why and how to fix it? TR Number: None Product: AutoPIPE Version: n/a Area: General, analysis Problem ID#: 75241 Answer: There are many issues that can cause an unstable system. Insufficient supports, not enough guides for wind or earthquake loading, insufficient soil stiffness in the vertical direction for soil problems. Evaluate your support arrangement for your particular loading conditions to see where the instability lies. Please see the following AutoPIPE help section: Help > Contents> Contents Tab> Bentley AutoPIPE> Frequently Asked Questions> FAQ document> FAQ #19. In addition, Please see the following AutoPIPE help section: Help > Contents> Search Tab> enter "E801" (include the quotes), press List Topics button, double click on the selected topic from the list provided to see more information. Again, there could be numerous reasons for the "Error "E801-1: FATAL ERROR: Unstable System" message to appear while running a stress analysis, see the following for possible cause and fixes: Scenario #1 After importing in the frame model through Pipelink. Error "E801-1: FATAL ERROR: Unstable System. Need support at node XX" is encountered. The AutoPIPE model (without the frame model) runs with no issues. I'm unsure why AutoPIPE would think the frame model is unsupported when the frame model runs with no problems in STAAD. FIX: While reviewing the AutoPIPE model, multiple imported beams were found to have their ends released in all direction, (i.e. on a beam dialog screen is the following option "End Releases: End-I/J Axial (translation), Y-Y and Z-Z". Therefore the beams were able to freely rotate. AutoPIPE requires that all components are restrained to some small degree in at least one direction. Checked one box for Axial (translation), Y-Y or Z-Z for all beams. Note: The STAAD model failed when loads were applied, it was also fixed. Scenario #2 Using copy / paste command to create a 10' x 10' grid of beams over 100' x100' area. when running analysis the message appeared. Fix: When using copy / paste command, only the initial pasted to point is actually connected. All other connections need to be manually connected. Every intersection across the 100 x 100 ' area needed t be correctly connected. Scenario #3 Similar to scenario #1, after importing in the frame model through Pipelink. Error "E801-1: FATAL ERROR: Unstable System. Need support at node XX" is encountered. The AutoPIPE model (without the frame model) runs with no issues. The model appears to be all correct and all the beam are were found to be all connected. Fix: 1. Go to Modify – Properties of Beam Section. 2. Select Section ID 2 (UA90x90x8) 3. Toggle from Standard to Non Standard Section type 4. Do not alter any properties, just click Apply and OK. Now the model is OK. The development team is looking into this issue and hope to have it resolve in AutoPIPE 9.6 and higher. Scenario #4 Back to back expansion joints where Torsional stiffness = 0.00. Fix: All AutoPIPE components must be connected to an object (i.e. anchor) to resist being rotated freely in any one of the 6 axis. In this case the expansion joint may be connected to an anchor through some piping but due to the "Torsional stiffness" = 0.00 the piping between the expansion joints would freely spin. To stop the warning from appearing, set Torsional stiffness = +ve value >0 (ex. 0.01). Scenario #5: With the following model and anchor settings: The problem with the model above is that there are no supports / anchors to stop the entire model from rotating about the X-axis as all the anchors are set with Rx stiffness = 0.00 and a Line Stop support only provides axial restraint. There must be some small resistance in All directions for the analysis to run. In addition, all the line stops have a large gap. Simply change an anchor to have some small amount of resistance (i.e. 0.10 Ft-lb/deg) for Rx and change 1 line stop to have a 0.00 gap or change 1 anchor X-Stiff setting to a small value (i.e..0.10 lbs/in) Scenario #6: The following warning message was found in the Model consistency check Report: * * * W A R N I N G - MODEL * * * W726-14: No anchors in current system Scenario #7: If all the beams in the model have been double checked to confirm connectivity. Check the Beam properties, notice that some values may be 0.000, as shown below: Increase the wall thickness and try to re-analyze the system. This may be an irrative procedure until the analysis is able to run. See Also Bentley AutoPIPE External Links Bentley Technical Support KnowledgeBase Bentley LEARN Server Comments or Corrections? Bentley's Technical Support Group requests that you please submit any comments you have on this Wiki article to the "Comments" area below. THANK YOU!
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