aluminum floor joists?

[Dawgs226]

for the first time i have seen these being used. i cant see them having any strength under fire. where can i find any info on these?

[ffmedcbk1]

do you have a link for these or a product name?

or is this the type you are talking about?

[ryguy1]

well alumin. melts at about 1200 degrees, so i wouldnt think it would last to long as a floor joist.

[gls4286]

There are two types of joists that may be what you are referring to. First, there are parallel chord wood joists. These are what is shown in the photo of the previous response. The chords (top and bottom) are flat 2x4's and the web members are made of either light gage steel (as pictured above) or 2x4's. These guys perform just like pre-engineered wood roof trusses under fire conditions. The steel press plates that keep the pieces together heat up when exposed to fire and pyrolysize the wood in contact with the tines. The tines then cannot 'bite' into the wood and the trusses collapse.

The second type of joists that you may be talking about are light gage steel. These are like the metal studs that are being commonly used for wall construction, only they are deeper and sometimes wider. The thin material heats up under fire load and can easily distort, which leads to loss of strength and support and then collapse of the floor system. Go to www.ssma.com to see more information on light gage framing.

These joists and the webs of the flat trusses are made of light gage steel, not typically aluminum...

Hopefully that helps answer your questions...

[ffmedcbk1]

do you have a picture of the second type?

[pgarland]

The attached is a photo of light gage steel framing used for the renovation of a Brownstone in Brooklyn, NY. Many contractors like using this instead of wood framing because of its lighter weight than engineered wood framing.

The photo shows light gage framing and structural steel framing working in combination. The floor has a plywood floor sheathing on top. There is additional light gage steel framing below the joists, but those are non-structural and they only are there for attaching the ceiling.