Hot rolled metal roof support

[Ceelo124]

I am designing a canopy roof for a structure that will be steel decking. I am trying to find information on using cold formed z purlins to connect the deck to. The hand calculations for cold form members are complicated and I can’t find many load tables in the USA. Am I able to just use a hot rolled channel instead of the cold form members? The design will become much easier this way and I would feel more comfortable sizing the member.

Another question is can you use TEK screws to connect the deck to a hot rolled channel or is it too thick?

 

[phamENG]

Am I able to just use a hot rolled channel instead of the cold form members?

I suppose that depends. Why were you using Z-purlins in the first place? Client requirement? Design criteria can come from a lot of places - as the engineer, it's your responsibility to know and follow all of them.

Another question is can you use TEK screws to connect the deck to a hot rolled channel or is it too thick?

That also depends. Look at the TEK screw design documents. They'll tell you what they are designed to do...

 

[Ceelo124]

Pham

I was using Z purlins to begin with because that is what I have typically seen for metal decking roofs. I have seen them mostly in PEMB. There isn’t a client requirement so I am no limited to using the Z purlins. It was more of a practicality question as I have not seen many projects using hot rolled members for purlins.

 

[phamENG]

I prefer not to use Metal Building System (MBS) components when not designing a MBS, and as I don't work for a MBS manufacturer, I never design MBSs. (Pet peeve: I don't like "PEMB"...nothing "Pre-engineered" about them anymore.)

By all means, use hot rolled stuff. It'll probably last longer in a canopy anyway. Where is it? Any chance of accelerated corrosion? Exposure to salts or chemicals? All those would eat some thin little Z-Purlins for breakfast.

 

[SandwichEngine]

I'm a PEMB guy. There may be some manufacturers who have span tables but if there are, I'm not aware of it. Since there are codes that allow an engineer to determine the strength based on the particular loading and support conditions, they just sell purlins and allow you to design them yourself. Doing otherwise would be like a steel mill publishing span tables for W-beams.

The best way I'm aware of to design or check cold formed purlins would be to download CFS (Cold Formed Steel. A license is only $120/year but they also have a lite mode that's free to download and might get you what you need.

https://www.rsgsoftware.com/index.html?cfsfiles

Pham,

I agree that there is nothing pre-engineered about PEMBs anymore. The name is a relic from when you could buy a building out of a catalog the same way you can now buy a shed at home depot. MBMA is trying to get the name changed to "metal building systems" wherever they are specifically addressed in any codes but to me, that's also confusing because you could have a ton of metal building systems that aren't a PEMB style building. For now at least, the name is just a misnomer.

 

[Bob Black]

In this case, it may be possible to use a hot-rolled channel instead of the cold-formed z-purlins. Hot-rolled channels are widely available and have well-established load tables, which can simplify the design process. However, it is important to ensure that the hot-rolled channel is compatible with the rest of the design and meets the required load capacity.
Regarding the connection of the deck to a hot-rolled channel, it is possible to use TEK screws for this purpose. TEK screws are typically used for attaching steel to steel, and they are available in a range of sizes to accommodate different thicknesses of steel. However, it is important to ensure that the selected TEK screws are appropriate for the thickness of the hot-rolled channel and that the connection detail is designed to resist the expected loads and forces.

 

[milkshakelake]

Agreed with using CFS software; that's what I use. Verify using some quick hand calculations or similar load span table (like compare a Z channel to a lighter gage C channel), because it takes some experience to click on all the right things. If you go the route of cold formed steel and want to use design tables instead of calculations and software, you can use C-channels like 1000S200-97 or something. Those have published load tables from different manufacturers. The advantage of cold formed steel is that it doesn't need a crane to lift into place.

If you go with hot-rolled steel, I think W- shapes are better than channels. Slightly more efficient because the wide flanges increase the moment of inertia and plastic section modulus. Also, I don't think they'd need bridging like cold formed steel does (and with other options like open web steel joists), though this also applies to hot rolled channels.