sloping moment connection @ roof

[sotir]

I have a situation where I need to design sloping moment connections at the roof in rigid frames for a 4 story medical facility. I cannot seem to find much information on sloping moment connections. So I have a few questions.

1) is there any good resource where I can find information about such connections?

2) if not then are there any design considerations that need to be applied due to the slope, or is it deisgned similar to a non-sloping moment?

3) since these moment connections are at the roof and a cap plate is needed for the column, would I then just use a bent plate that would be the top flange plate of the moment connection then bent over the column and also be the top flange flange plate on the moment connection on the other side?

Any other considerations, concerns, design concepts would be welcome.

Thanks in advance.

 

[shemp]

I asked this same question last year. The response I got was that a sloping moment connection is designed the same as a horizontal one, except the force from the flange plate should be resolved into its components when considering column stiffener requirements.

I think instead of using a bent flange plate over the top of the column, I would look into using a flat cap plate with sloping flange plates coming off of that. The reason being, at the location of the bend in the plate, a vertical component of the plate's axial force will be developed. I would rather have this "bend" occur at the column flanges (which would be the case with a flat cap plate), than at the centerline of the column (which would be the case with a bent plate). You would just have to look at the vertical component of the flange plate force and see if the column web can take it. I'm just thinking that it would be better to have this stress concentration at the column flange where there is more area, than at the column web.

Out of curiosity, how will you do your detail so that the flange plate doesn't interfere with the decking or roofing materials? I had trouble with this detail and I'm wondering if you've come up with a good solution.

Shemp

 

[sotir]

Thanks for your input shemp.

For the decking, well, I was contracted to perform the calculations on the connections only, but depending on the design of the building this could be accoounted for in a few different ways.

If there are purlins over the main girders to support the deck then this should bring the elevation high enough to miss the flange plates and bolts.

If no purlins then the decking would probably have to be notched around the connection area and basically form a crouwn at each of the columns. In this case there would have to be some framing angles around the connection to give support to the decking.

I have also heard that on occasion that the deck can be deformed enough at these locations to fit over the top of the plate and bolts. If using the decking as a diaphragm then I don't think this is the best way.

Lastly, if none of these other ways are feasable then the decking elevation can be raised by use of insulation or shims, to bring it over the top of the bolt heads.

That's about all I can think of. The engineer on this project called out for flange plate moment connections throughout the project so I assume he has taken this into account. If not, I'll probably be getting a phone call!