Sloping Top Chord of Steel Joist

[jmp02t]

I emailed a rep from Vulcraft a few days ago and haven't received a response from him yet, so I thought you all might be able to help me.

1. Are only long-span joists able to have a double-pitched top chord? Can K-series joists span a ridge line with the top chord having a double pitch? The pitch of the roof is 1/4” per foot.

2. I have a long-span joist 40’-8” long being used as a girder (with the double-pitched top chord) to pick up a point load (~30k) from a W24x55 beam that is running perpendicularly to it. This beam is bearing a mid-point of the joist only. How do I choose and specify a joist girder for this condition? How would you suggest connecting the beam to the joist (not the joist to the beam)?

Thanks everyone!

 

[JAE]

I believe K joists can have any type of top chord - just carefully and correctly detail the dimensions for them.

Not sure I've ever seen a WF beam frame into a joist girder. Just doesn't feel right. I know it can probably be done though.

 

[msquared48]

As for your second question, you really need to talk to Vulcraft as their design of the girder will be impacted, plus they probably have their preferred way of doing these things anyway.

No reason to reinvent the wheel here if you know what I mean.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[a2mfk]

Both are common situations, just be clear in your drawings what you are doing.

I believe the preferred connection will be a vertical angle (web) in the steel joist where your WF can frame into the angle. That way you have a standard steel shear connection and your beam is properly braced for stability purposes. When Vulcraft calls you back you can bounce that off of them. Of course, clearly indicate this on your drawings, they can clarify this during the shop drawing process.

 

[MiketheEngineer]

If you have enough money - SOMEBODY will do it for you.

 

[jmp02t]

I spoke with a colleague that's an engineer at another joist manufacturer. His suggestion was to name the joist girder as a 26k9-SP. (Parallel joists are also 26K9, so it will make more sense to keep the depths consistent.) The SP will indicate that they will have to design the joist for the 30kip point load applied by the beam bearing to it.

Also, similar to a2mfk, he said they would provide an angle connection to the beam and that I need to specify the leg length of the connecting angle and bolt hole diameter to connect to the web of the beam.

Thank you all for your suggestions and help.

 

[a2mfk]

Since that angle connection will likely have some eccentricity to the neutral axis of the joist, I would provide diagonal bracing from the bottom of that angle up to the top chord of the adjacent joist to resist the torsion. Don't leave it up to the joist mfr or the shop drawings, just detail it on your CDs. You may also need to consider bending in the angle since it will not be braced along its length by a wide flange web like a normal shear connection.