Timber Truss Gusset Plates With Screws

[stennist]

Historically, timber truss gusset plates have been connected with through bolts, but over the past decade, the wood screw industry has made some amazing developments in wood screw technology. I have been considering the idea of designing some timber trusses that have the steel gusset plates connected with Simpson SDWS22312DBB with STN22 (Hex Head Washers). This would give the appearance of a bolted connection for aesthetics, but would use fastener technology that is much easier to install. Such trusses would be able to be constructed by carpenters that aren't necessarily the most skilled. Fasteners like this are widely used for attachment of hardware in post and beam construction so why couldn't it be applied to trusses. I was curious as to others opinions on this topic and if I am overlooking a major benefit to through bolting. Here is the list of advantages/disadvantages I have thus far:

Advantages:
1. Fasteners are easy to install. No predrilling is required and holes do not need to be perfectly aligned to the gusset plate on the reverse side.
2. Slop of bolts in holes at bolt groups is eliminated.
3. The load is spread to many more fasteners which should provide for a much stronger wood joint.
4. The risk of splitting of the timbers during shrinking and swelling would be reduced vs that of bolts.

Disadvantages:
1. You loose the clamping effect of through bolts, but I am not so sure this even exists a few years down the road after the timbers shrink.
2. Many more fasteners to purchase/install.
3. Not the norm that building officials are accustomed to.

Thanks in advance for any feedback you provide.

 

[KootK]

I see it the same Stennist. If the numbers work, there is much to like about using screws. One, additional, disadvantage might be that the use of small, more distributed fasteners may force you to increase overall dimensions of the fastener group and thus exacerbate shrinkage issues. That said, I suspect that this would be manageable in most cases.

 

[dik]

Glulam rivets?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[1503-44]

Too much time to build.
These can be fabricated in minutes.

https://duckduckgo.com/?q=gangnail+trussplates&t=brave&iax=images&ia=images

 

[Pmtottawa]

Not today they can't.
Current market here is ottawa is insane.
All the 3 big manufactureres in town are quoting delivery either late this year or early next year

They aren't even looking at projects for layouts for permit...

P

 

[1503-44]

Had no idea.
Can you get enough screws and wood?
Carpenters?

 

[kipfoot]

What I like about this is that the STN bolt has the nub that nests in the hole in the steel plate which would allow contact for load transfer...the screw head also nests in the top of the bolt.

Also, you could use a longer SDWS screw if you needed to; you're not limited to 'outdoor accents'.

 

[EdStainless]

Since the forerunner of gangnail was a steel plate with holes for nails to be driven through I don't see why the numbers for screws wouldn't work. It will take quite a few fasteners so be prepared.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[XR250]

The Simpson Screws you selected have threads bigger than the shank - which would leave the hole in the steel too big.
I would consider the SDS screws instead.

 

[stennist]

Thank you all for the feedback thus far. I do agree with you KootK that the size of the fastener group needs to be considered with regards to shrinkage. The timber trusses I would design with this method would not have astronomically large forces in the members and would probably be extremely oversized timbers in order to give the appearance that people are looking for in the great rooms of their homes. So I think things should be OK with regards to this potential issue.

dik, Glulam Rivets don't give the look that most people are searching for, but I do like the deign analogy. They are pretty similar concepts with numerous fasteners on a tight spacing. This will be a good place to research with regards to shrinkage issues that were discussed above.

1503-44, I do like those nail plates for trusses that get covered with drywall or other sheathing. I am discussing exposed timber trusses though. Nail plates are not very pretty to look at.

kipfoot, I had chose this particular combination because it gives the same appearance as a bolted connection, but would theoretically be a lot easier to construct. I am also considering other options (see below), but the prefinished look of the outdoor accents would be desired in some instances. I agree the nub on the STN22 Hex Head Washer is a great concept.

EdStainless, I agree the numbers should work, but why hasn't there been more people doing it. Perhaps as I dive in further I will find that number of fasteners or fastener group size will make this an unappealing option. With regards to number of fasteners, a 3/4" bolt in double shear through 1/4" steel gusset plates and a 6x timber provides about 3844lb for snow load durations. The screw and washer combination I proposed provides 736lb each for snow load durations. With one on each side you get 1472 lb per fastener line. So it takes about 3 fasteners per side to equal the strength of (1) 3/4" though bolt, but slapping a plate on and driving 3 screws would be a lot faster and provide far less slop than tying to drill through and have both plates match up at all locations. See further discussion below with regards to a different screw option.

XR250, yes the threads are bigger than the shank, but the hex head washer has a nub that fills the hole to engage the plate. You have to use the combination of screw and hex head washer or it doesn't work. See picture earlier in this thread for the washer. After further research, I am thinking the combination I proposed might have a deal killer requirement. These screws are required to be spaced 4" apart with 6" between rows to achieve full working load. This will make for much larger group sizes than standard bolting and the gusset plates will be costly. I looked at going to a SDS option. They would require (4) fasteners on each side per bolt. You can get stagger these on a 1.5" spacing with 1.5" between staggered rows and 3" between the staggered lines. I think SDS might end up being the most practical option with regards to group size and size of gusset plates required.

 

[XR250]

OK, did not catch the STN22 - interesting.

 

[1503-44]

Yeah, not pretty. Glue some plastic sticky sheet over them?
I could say the same about gussets and screws though. And they're harder to hide.

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