Referencing the image above.
1. Which parameters are required for STAAD to calculate Cb automatically when Cb is set to 0.0?
1.1. For the beam in the image above, which segment is considered by STAAD to determine Cb?
1.2. How does parameters UNL and UNF affect the consideration of segment for Cb calculation?
2. In connect series, how does physical elements affect automatic calculation of Cb?
3. In AISC UNIFIED 2016 the Cb default value is 1.0 against CSA S-16-09/14 which is 0.0, why is AISC manually calculated and CSA automatically calculated?
The Cb is not affected by any other parameter. When Cb is set to 0, which is the default, STAAD.Pro calculates the value automatically based on the moments at various locations along the member length. For the beam in the picture above, STAAD.Pro would consider the left segment when calculating the Cb for member 12 and the right segment when calculating the Cb for member 597. The UNT/UNB/UNL does not affect the Cb. The physical member modeling in CONNECT Edition is limited to modeling and analysis for now and does not get carried over to the design phase as yet. That is something that will happen in the future. The default value of Cb is 0 for both AISC 360-16 and CAN/CSA S16-14 and so by default the value is auto calculated.
Thank you for the response. I should have mentioned it earlier but I am using Staad Version 22.00.00.15.
Based on your reply, I have the following follow up questions:
1. Help within STAAD mentions the default value for AISC Unified as 1.0. Is this wrong?
The following snapshot is from D1.4.6. explaining the design parameters.
2. This is just a confirmation. My understanding based on your explanation regarding the automatic CB is that it is calculated by STAAD for each individual elements irrespective of whether the beam is actually laterally restrained or restrained from rotating about the longitudinal axis. And there is no provision to explicitly state the length of beam for which the restraint is applicable (from the operator's point of view) using the design parameters. Is my understanding correct?
3. A follow up to #2. In the snapshot below (please consider the connection as fixed between column and beam i.e. a fixed frame), if a beam is divided into elements (12 and 597) then the CB values, with respect to each element comprising the beam, will be automatically computed when CB set to 0 based on the moments of individual elements and assigned to it i.e 12 and 597, respectively, which is definitely not correct. So CB has to be manually computed for the whole beam under such case. Is my understanding correct?
4. Which design condition utilizes the UNL and UNR parameters?
1. Yes the documentation seems incorrect. I will talk to our documentation team about it. The description within the Design Parameters dialog box is correct ( picture below )
3. Correct. For members that are split into segments you should input Cb directly.
4. UNL and UNR are used in connection to Lateral torsional buckling checks when the bending is about the local y axis.
Adding to the point 1, I think what has happened is that the default for Cb used to be 1 for earlier versions of the code like AISC 360-05 and AISC 360-10 and since the design parameter section in the Help documentation is generic for all the versions, it remained like that. However for the AISC 360-16 there should at least be a note mentioning that the default is 0 for this version.