Single Plate Shear Connection - Bolt Group Eccentricity

[VTStructures]

Hi All,

US based, designing with AISC 360-16 (15th Edition). I just recently started using RISA Connection to help with steel connection design efficiency. I'm still in the process of vetting the calcs, and came across an unexpected result using single plate connection to a column. When connected to an HSS wall, the software automatically treats the connection as the Extended configuration. This causes the program to design the bolt group for the full eccentricity from the face of the column to the bolts. If I switch the column to a wide flange (flange or web connection), then it allows for the Conventional design checks, which uses half of the actual eccentricity per AISC table 10-9.

Now, it makes some sense to me that the more flexible support condition of the HSS wall could allow for additional rotation. This in turn might justify designing the bolt group for the full moment. I was wondering if anyone had any references that indicated you had to use the Extended design checks when connecting to face of HSS. I don't mind erring on the conservative side, but there may be a time where I have to explain to the EOR/Contractor why I am calculating a lower shear capacity for a standard connection than is listed in the tables in the manual.

(For what it's worth, I have also reached out to RISA support and am waiting to see if they can clarify).

Thanks all!

 

[onlym112]

There is no reference that tells you that you need to connect an extended shear tab to an HSS column. If I were you, if possible, I would connect the HSS column to the beam with a Single Welded-Bolted connection. If that is not possible for whatsoever reason, I would then use a standard shear tab. For information on shear tabs, I recommend you read the following papers:
1) A Shear Connection Extends Its Reach, (Muir, 2017)
2) Development of a New Design Procedure for Conventional Single-Plate Shear Connections (Muir, Thornton,2011)
3) Design of Unstiffened Extended Single Plate Shear Connections (Muir, 2009)
4) On the Need for Stiffeners for the Effect of Lap Eccentricity on Extended Single-Plate Connections (Thornton, Fortney, 2011)
5) Tosion of Rectangular Connection Elements (Bo Dowswell, 2017)

Hope these help.

 

[structSU10]

Look AISC chapter 10 about shear tabs (in the 14th edition manual it starts at page 10-102). there are limits on when you can use conventional versus extended - the one that may control is thickness of the web you are attaching to. There is no explicit discussion about HSS automatically forcing a certain analysis type.

There is also discussion about using the extended shear tab but dumping some of the moment back into the column if it can handle it to limit the bolt group eccentricity.

 

[VTStructures]

Thank you both for prompt and thoughtful responses. I consider myself to be quite familiar with shear tab design and the limits on use of the Conventional versus Extended checks. I have always treated a shear tab to the face of an HSS as no different than to a beam or column web (with the necessary checks for the HSS wall of course). The connection I am analyzing meets all of the criteria for Conventional, including web/plate thickness. But, for some reason RISA Connection automatically changes it to Extended if I substitute in an HSS column instead of a wide flange. It made me wonder if there was a provision I am missing.

I did hear back from RISA and they were not able to provide any guidance. They just regurgitated info from the help section about how to calculate the eccentricity coefficient of the bolt group. Which is funny because somewhere along the line one of their developers made a conscious decision to modify the eccentricity depending on whether the column is WF or HSS. I'm just curious why.

I think going forward I will take the hit on shear capacity when it does not change my design, but hand calculate the bolt shear when needed to more closely mimic the capacities that are shown in the AISC tables.

 

[onlym112]

I just wanted to clarify my initial post. By "Single Welded-Bolted" connection I was referring to a single angle connection where the long leg is the the web-framing that is bolted to the beam and the short leg is welded to the column. In most cases this is always sufficient. If not I would a standard shear tab for an HSS Column connection. If for some reason there is coping involved and you want to avoid the copes, extended shear tab is the way to go. I like the single angle welded bolted connection because it is economical and you can also ignore the effect of eccentricity if your web framing leg from your bolt line to the face of support is less than 3".