Residential Wood Deck Brackets (Standoffs)

[bookowski]

Has anyone used this product or similar? I have been asked by an architect to use this product and have not used anything like this before. It is essentially an aluminum 'I' with one flange bolted to the rim joist, the other flange attaches to a deck ledger. I see the benefit in waterproofing. The eccentricity worries me, it looks like I'd want a tension strap to a joist at every bracket to feel comfortable that I'm not going to roll the rim over. The company doesn't seem to have any engineering support - on their website they say that they recommend 6ft. to 8ft. spacings which seems excessive to me. Any experience with these?

http://deckbracket.com/

 

[theonlynamenottaken]

There is a link to their ICC-ES Evaluation Report. It gives the bracket an allowable capacity of ~1000 lbs at the deck ledger bolting flange. The report really only covers the bracket itself, because within the report it does state, "Details to resist the effect of torsion in the rim joist shall be submitted to the code official." This is where your tension strap to joists would come into play.

I like that they've listed one of the features of this bracket as, "Frustrates insects".

 

[Splitrings]

Looks like you have two choices; resolve the torsion in the rim board either at floor joists or through the plywood deck attachment points. Considering the precision I have seen some carpenters use when laying down plwood decking, my vote would be straps at every floor joist!

 

[bookowski]

I agree - I'm thinking of putting a simpson deck connector strap (

http://www.strongtie.com/products/connectors/DTT2.asp)

at one of the top through bolts on every bracket.

 

[Splitrings]

Looks like the bolt spacing on the bracket is around 7". I am guessing your floor joists won't be that close. I was thinking of using a strap tie on every floor joist that wrapped down over the rim board. An "L" shaped tie.

 

[bookowski]

Splitrings - What do you think about the attached? Based on the 7" dimension that you mentioned the bracket would have to be offset appropriately for this detail to work. It's a bit funky because the tension tie would be only be on one side of the bracket, although the other side would still get a through bolt to the rim which in theory has some restraint from the sheathing.

 

[msquared48]

Well, I hope they provide or specify the use of aluminum bolts instead of steel...

Mike McCann
MMC Engineering

 

[Splitrings]

The connection you propose would load the bracket eccentrically, as one upper connection would be stiffer than the other. Is the acceptable??

My thought was to strap the rim board to each joist. That way it didn't matter where the brackets end up. Assume the worse case where the bracket straddles a joints and design the ties for this tension. You probably should look at the case where the bracket falls in the middle of two joists. Will the torsion cause servicability issues with teh rim board??

The report does state a SYP or Douglas Fir (S.G. >0.50) was used. If you use a TJI Rim Board you'll have to determine if it is accepatable.

msquared48 mentions aluminum bolts. A structural aluminum bolt? We have always used stainless steel bolts with aluminum. It redues the dielectric action but doesn't eliminated it.

 

[msquared48]

Splitrings:

I was being a little facetious there on the bolts, but that is why I am always concerned with aluminum to steel connections.

And the detail I do not like at all. Supposedly, the torsion is taken out inside the house with the strapping, but there is nothing to take out the torsion of the connection of the deck member outside. There needs to be another strap at the bottom of each and every joist here too.

I would never use this product... Just does not feel right.

Mike McCann
MMC Engineering

 

[Splitrings]

Mike:
I figured you were in regards to the bolts but this day an age there is always some new out there.

I didn't even look at the connection of the deck joists to the ledger board, but the same issue exists here! I guess that is why we carry the loads from the point of application to the foundation!

I am not convinced this connection is worth much either. It looks like a nightmare to install siding around. Standard ledger board, ice & water shield and flashing.

 

[msquared48]

Exactly.
Currently, the rim joist of the deck is seeing cross-grain bending without any tension ties. Classic...

Mike McCann
MMC Engineering

 

[bookowski]

Do you mean cross grain bending induced by lateral load on the deck? The deck will need tension straps to the bracket to satisfy code requirements - those just weren't shown because I was focusing on the bracket itself. I agree it's not a great detail which is why I was inquiring if anyone had done this. It would not be my choice but the architect likes it - I'm just trying to figure out if this is a definite no or more of an... eh, not great but if we put enough detail in we can make it work. I know that it's easy to say you would never do a detail on a forum - but I'm just wondering if the detail is so bad it's worth fighting over.

 

[msquared48]

bookowski:

No. I was referring to moments induced by gravity forces. I was unaware of the additional strapping. That seems like an awful lot of extra hardware to justify the use of the bracket.

Lateral is quite another issue here. Is there a wood infill of the gap with an infill 2X nailer to the house to transfer the lateral shear?

Mike McCann
MMC Engineering

 

[XR250]

Agree with M^2. Obviously designed by a non-structural engineer.
I can't actually believe it got ICC certified - what a joke! They will certify anything
"yes, the bracket can take the load as long as you can figure out how to deal with the torsion" - good luck.
Kind of like those "lite steel beams" they were peddling. Works great as long as you can keep them from twisting

 

[wannabeSE]

I noticed a couple things in the bracket's ICC report

1/2" hot dipped galvanized A307 grade A or SAE grade 2 bolts with 1" diameter flat washers are required.
The allowable load is multiplied by 0.4 for wet service.

 

[bookowski]

The company sent me a copy of their test report. They didn't just test the bracket although the rig was a bit funky. They did make some attempt at simulating a 2x8 p.t. ledger attached to the bracket and loaded that. The report actually states an average failure load of 10k and then states that this results in an allowable load 2,400lb vertical - not sure where the 1,000lbs came from. I did the seem the wet service note - I would assume that this would follow typical use for dowel fasteners in wood, i.e. use Cm as reqd.

I agree that it doesn't seem great which is why I was inquiring if anyone had used anything similar - although I can't say that I was quite as offended by the detail as some others on here, I've definitely seen worse.