Hello all, I have a rather unique problem that I could not find a solution to via Bentley STAAD forums or online.
I have errors in defining a multilinear spring in the global -X direction for a movable structure subject to a large asymmetrical load. I am analyzing with STAAD Pro Advanced CONNECT, where I've modeled two springs as multilinear springs, with 0 kip/in stiffness from 0” to 0.25”, and nearly infinite stiffness (1x10^8 kip/in) beyond 0.25” to model a constraint on both corners of this structure. This client requires confidentiality due to the nature of this analysis, so unfortunately I cannot upload my model or provide visuals. This structure can be visualized as a large steel rectangle that hits the two immovable boundaries in the top right and lower left corners of the structure, because this asymmetric hoist load is in the lower left quadrant of this rectangle.
Of the two nodes assigned to these multilinear springs, the top right hand node (Node 100) is intended to deflect up to 0.25" in the +X coordinate plane, until it hits an immovable object modeled with massive rigidity, The bottom left hand node (Node 200) is intended to deflect -0.25" in the X coordinate plane, until it hits an immovable object modeled with massive rigidity. This is assigned as shown below:
SUPPORTS10 50 FIXED
100 FIXED BUT FY FZ MX MY MZ KFX 1
200 FIXED BUT FY FZ MX MY MZ KFX 1
MULTILINEAR SPRINGS100 SPRINGS 0 0 0.25 1e+8
MULTILINEAR SPRINGS200 SPRINGS 0 0 -0.25 1e+8
What is odd is that Node 100 behaves correctly- ts maximum deflection for the fully-factored load case is +0.250", and it displays a large -X reaction with no other reactions. However Node 200 does not deflect at all (it says it deflects 0.000") while simultaneously outputting a large global +X reaction load at said node.
This result of course makes no sense, because the expectant behavior should be either:
How do I fix this Node 200 problem? I have thus far tried 4 combinations of defining +/- 1 (kip/in) in KFX and +/- 0.25 (inches) for Node 200, assuming this was a sign convention issue- however the 3 of these options give extremely large displacements well past the -0.25” limit with a 0 K +X reaction, and the only reasonable combo was that shown above. I've written the analysis with SET MULTI 2, and this same problem persists no matter how large or small I make the test hoist load in this lower left quadrant of the structure. Any help would be greatly appreciated!
Adding to this, in all the trials I've run with small tweaks in this model, the Analysis Output file always states "MULTILINEAR ITERATION TERMINATED WITHOUT CONVERGENCE AFTER 201 CYCLES."
Please upload the .std file.
Thanks for the quick reply Sye. Unfortunately we have a strict confidentiality agreement with our client due to its government affiliation, so I would not feel comfortable posting it even in a private message. I can however copy and paste excerpts from the input file or answer any questions you may have on the model.
You may create a service request and attach your model with it. Service Requests are only accessible to Bentley colleagues in technical support.
That is good information to know Sye. I will run that by our structural team and see if everyone involved would be comfortable with doing so. Unfortunately this means that I wouldn't be able to submit the model to Service Requests until early next week at the soonest, assuming everyone on the team approves of doing so.
I've run this by the team and they'd like to send it out to you immediately. How do I send the file through Service Requests?
Please use the process outlined in the wiki below
https://communities.bentley.com/products/w/products__wiki/24845/service-request-manager
Good morning and thank you Sye, I've just uploaded the model and accompanying .dxf file to the Service Request Manager.
Good afternoon Sye, have you been able to open/explore the model as of yet?
I just replied to the service request with my suggestion