Steep Steel Joist Roof

[TXEng-USA]

I have a job which will have very steep (8.75:12) roof framed out with steel joists. I am working on the detail and would appreciate it if you all would review the attached details and provide your input/recommendations.

My primary concerns consist of:

[ul]
[li]Diaphragm shear transfer at the perimeter of the roof (detail 3). [/li]
[/ul]
[ul]
[li]Diaphragm shear transfer at the ridge (detail 4). My intent is to make the deck behave monolithically. [/li]
[/ul]
[ul]
[li]Bearing seat details, I am utilizing Bent PL3/8" for bearing seats, is this conventional construction at this depth?. Also, I have seen in other consultants details that they don't design the bearing seat but appear to leave it up to the joist engineer. Is this standard practice? [/li]
[/ul]
[ul]
[li]I have added a PL1/8 on top of the HSS collector to match the slope of the deck. Is there a better way to ensure a positive shear transfer from the deck into the collector? [/li]
[/ul]

 

[JedClampett]

I like the details. I've seen the same details (with some minor changes)used before and have probably used them myself. I'm not sure I understand what the HSS is transitioning to on the steeper slopes, but I've only looked at this for a couple of minutes.
I think that the joist supplier would prefer designing their own seats, but we've had some flaky experiences with them recently, so who knows?

 

[Deker]

For detail 3, I would prefer to use a single bent plate on top of the HSS to support the sloped deck bearing rather than the two-plate assembly you are showing...I'm not sure that the weld you are showing between the 1/8" plate and the flat bar would actually be a prequalified fillet weld. The HSS shims for diaphragm shear transfer are common practice. For detail 4, I would prefer a detail similar to detail 3, but with added tie plates across the joists at your chords...what you are showing would also work, though. I agree with Jed that the joist supplier should design the bearing seats, but you will need to assume a seat depth for detailing. You should probably call the joist supplier to get an idea of what they prefer. This document may also help: Link.

 

[JAE]

Check with your local joist manufacturers. Typically seats are created as part of the joist, not something you need to detail as it would simply be a part of the joist design and fabrication process.
Use of the chart to show different joist depths based on slope is applicable - but again, the manufacturer will take care of this.



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