Hello community,
I am designing steel structure as per Eurocode EN 1993-1-1 (without any National Annex) with custom response spectra (elastic) for seismic loading. Now due to erection reasons, I have to make/assign pinned connection to beam 1320 & 442.
Before assigning the pinned end connection to beams 1320 & 442, beams 89 (column) had utilization ratio 0.6 for load combn 111.After assigning the pinned end connections to beams 1320 & 442, the ratio has changed to 1.012 for load combn 111. This has changed drastically.It can be observed that the mass participation factor as well as the the mode frequency is changed very slightly.So what could be the reason behind the sudden change in utilization ration for beam 89? Is this the issue with my STAAD version?STAAD Pro version 20.07.11.90I am uploading the file via secure fie upload. Please also have a look at the file wrt "procedure / commands" used.
Thank you in advance.Regards,Vishal
I see a small increase of utilization ratio for column 89 from 0.638 to 0.645 when member releases for beams 1320 and 442 are assigned. I think such increase could be expected due to redistribution of member forces when changing member releases. By the way, I am using STAAD.Pro version 22.01.00.39.
Answer Verified By: Vishal Girase
Thank you for your prompt reply.
It seems very strange. Few more questions, request you to clarify.
A) Is my STAAD version (20.07.11.90) old so that its solver (analysis point of view & not code check point of view) may have errors and the same are revised or changed in new versions such as yours? The results should match, don't you think?
B) When does STAAD check for torsion as per Eq. 6.1 of EN1993-1-1 (elastic verification) & when it is neglected?
C) The increase utilization ratio corresponds to torsion check when member end connections are released.
Please refer below observations
Without member release at end connection ratio = 0.6 for load case 111 & criteria - 6.3.3-662
Max torsional moment Mx is 5.74 kg-m (for load case other than 111), Mx = 0.98 kg-m for load case 111.
With member release at end connection ratio = 1.012 for load case 111 & criteria - 6.2.7(5) (torsion check, elastic verification)
Max torsional moment Mx is 5.4 kg-m (for load case other than 111), Mx = 1.028 kg-m for load case 111.
D) Finally, why is this happening? And what is the solution, other than upgrading to latest version?
Look forward to hearing from you.
Kind Regards,
Vishal
The analysis results are the same (or very close) in both STAAD.Pro versions.
I think the reason of this difference is a minimum torsion value which is considered to trigger the use of cl. 6.2.7(5). As I understand this limt is 1.0 kg-m in STAAD.Pro V8i. So when you run the model with member releases, the Mx value is 1.023 kg-m which is more than 1.0, so check of cl. 6.2.7(5) is performed automatically. If you would use a design parameter TORSION 3 to ignore all torsion checks, you would get a very close unity ratio to the case where member releases are not used.
In the case without member releases, the Mx value is 0.98 kg-m which is less than 1.0, so check of cl. 6.2.7(5) is not invoked.
However, I would recommend you using the STAAD.Pro CONNECT Edition instead, as the support of STAAD.Pro V8i version 20.07.11.90 will be stopped at 1st of January in 2020.
Thank you for the clarification.
Few last questions
1) As you said, for V8i version 1 kg-m is limit to invoke torsion check. Is this limit changed for CONNECT edition? I can not apply torsion 3, since higher torsional moment value exists for other load cases / combinations and torsion.
2) What if I dont specify any torsion command. It will by default use TOR0, am I right?
Modestas said:However, I would recommend you using the STAAD.Pro CONNECT Edition instead, as the support of STAAD.Pro V8i version 20.07.11.90 will be stopped at 1st of January in 2020.
Thanks for the information.
1) Yes, I think this limit is different in the CONNECT Edition.2) Yes, TOR 0 is a default value.