Treated Wood Nailer On Structural Steel 1

[Loui1]

I have a steel beam with a wood 2x nailer to allow roof truss attachment. The nailer must be fire treated. How do you prevent the corrosion of structural steel? Are there any products out there that isolate the steel from the treated wood?

 

[structuralaggie]

I'm assuming fire treated wood roof trusses too? That doesn't seem to make sense. Why not light gauge?

 

[Loui1]

No, they're lightgage roof trusses. The contractor goofed the t/steel low by 1 1/4" and is looking to make up the difference with wood blocking. Per code and architect, that wood needs to be fire treated.

 

[CJJS]

Check with different FRT companies. Some claim their product does not corrode metal. Dricon for example makes this claim.

 

[structuralaggie]

I'm not one for mixing in wood when everything else is steel. I would be creative with a clip angle and misc. structual steel components if that is an option.

 

[JAE]

Loui1 - why can't you simply specify some building felt, or other gasket type material to separate the two?

 

[archeng59]

adding a heavy felt or plastic shims between the treated lumber and the steel beams and the trusses would isolate the treated lumber. the next issue is the fasteners used to attach the lumber to the steel beam and the trusses to the lumber. heavy galvanization (G185) would be required to help reduce fastener corrosion, but that likely won't eliminate it.

 

[whyun]

If wood isn't already installed and occuring in only a few locations, can you go with a cee shaped 1/4" bent plate with web set at the desired elevation?

JAE's suggestion is good for separating the lumber from the beam top flange and archeng59's concern about the threaded rods is valid.

 

[Loui1]

Isnt felt paper pourous? If there is some literature out there that covers this subject, please post it up. I've seen felt paper used like this on rare occasion, but I've never seen anything saying that it actually works.

I'm not aware of any gasket material that will serve this purpose.

Thanks Schwartz, I'll look into the treatment chemicals.

 

[Loui1]

Just found this elswhere.

http://www.graceathome.com/pages/decking_faq_corrosion.htm#EIGHT

Can I use felt, building paper, housewrap or similar materials as barriers to prevent corrosion?
No. These materials may not effectively separate the dissimilar metals in the wood and in the metal components. They offer NO protection at the key potential corrosion sites where fasteners penetrate the barrier.

It's for CCA and protecting metal deck, but it's the same idea.

 

[rgerk]

Loui1,

I have to side with structuralaggie on this one. Don't mix wood when everything else is steel. I have been providing connection details for the light gauge truss industry for the past 4 years and I always hated seeing a wood nailer being spec'd out on top of steel beams and masonry walls in the contract drawings.

Using a wood nailer creates a problem of what fasteners, more importantly, how many fasteners to use for attachment. The norm is #10 screws with some type of light gauge bent plate. #10 screws have very low pull-out values in wood. The truss connections will be dictated by the uplift value on the trusses anyway.

Try using some type of HSS spacers, 1-1/4" steel plate, or build up a light gauge metal spacer. You will use fewer fasteners and not have to worry about the interaction between the fire treated wood and the steel.

Don't let the contractor bully you on this. If you don't want to use wood, tell him no. It's your building design.

 

[lkjh345]

Loui1:

Simpson recommends Grace Vycor Deck Protector membrane to seperate their metal connectors from pressure treated lumber with ACQ or CA treatment( Simpson Technical Bulletin T-PTBARRIER05). You might inquiry from Grace weather this material would also provide a barrier to fire treatment chemicals.

 

[unclesyd]

What I've seen used is Butyl tape. The type used for roofs, flashing and weather seal around windows. They used the tape between the wood and beam and also between the wood and roof panels. Just saw a similar construction where they were using a Boric treated wood, dyed brilliant green, attached to the beams with Tek screws, no tape.