Deck Lateral Load Connection

[HardleyWorkin]

And here's another angle. Say the deck is in the inside corner of an L shaped house. Either way it moves in the lateral direction, it will be sliding along one or the other wall. Every fastener into the wall is now loaded in shear, all along the whole length of the ledger connection to the wall. So where does the tension tie go, and what does it supposedly do?

I'm just asking.

[kfc510]

And here's another angle. Say the deck is in the inside corner of an L shaped house. Either way it moves in the lateral direction, it will be sliding along one or the other wall. Every fastener into the wall is now loaded in shear, all along the whole length of the ledger connection to the wall. So where does the tension tie go, and what does it supposedly do?

I'm just asking.

Well, it depends on the construction of the deck. Most decks these days do not have strong structural connections between the decking and joists, and therefore are not viewed as a rigid diaphragm like a nailed subfloor.

So the inside corner of the deck is indeed constrained by the shear resistance of the bolts. But the outside corners are not. So that's where you'd put the hold-downs.

[kfc510]

Andrew says above, "I obtained permit 2 weeks ago and was given two choices for deck, free standing or the Simpson thru bolt product KFC10 pictured." I guess my question is, when would that Simpson connector experience its rated load? What are the actual conditions that would require that restraint?

There's a Simpson resource on this topic here ->

http://www.strongtie.com/ftp/bulleti...KLATLOAD11.pdf

It says, "These loads can result from wind or seismic forces acting on a deck or from occupants on the deck moving around." There's a big difference between wind and seismic, and if people moving around is as strong as seismic, then we need to design all buildings everywhere for seismic, because people everywhere move around. The Simpson connector has a rated load, and I would imagine, as a lay person, that if it's adequate for seismic, it's oversized for "occupants moving around" and so which one is it sized for?

Maybe there's a reasonable explanation, but I just haven't heard it yet. I get how one benefit of codes is to keep hacks from building stuff, but that's not a justification for making the codes arbitrary. If anything it's a reason to make them reasonable and prudent, rather than give people an excuse for saying it's all just a game. And in any case hacks don't follow any of the codes, whether the codes are strong or weak, so ... I would vote for having the codes be clearly justified.

And I guess I am dubious that any engineer outside of seismic zones has demonstrated that this connector is needed to restrain a deck frame in the lateral direction, in the absence of earthquake risk, or proven that it's the only way to do it. So if building officials are requiring that people either do this or a free standing deck, well, I think they should explain why.

I mean, and, not to nitpick, but the code calls for two of these connectors, one at either end, regardless of the size of the deck. Surely the size of the deck influences the actual design load experienced. But there's no guidance on that ... four by six deck, or 16 by 32 deck, it needs two Simpson tension ties. A reasonable person could call that arbitrary and say, well, if this is a small project in an area with a low design wind speed outside of a seismic zone, maybe I should not have to tear up the dining room floor and nail in a bunch of blocking just to install a tension tie.

Don't get me wrong - Simpson connectors usually make stuff stronger. But when is it overkill?

Lots of good questions there.

1. "What are the loads resulting from, seismic, wind or people moving?"

Well, you say seismic and wind are different. The way the force is delivered to the structure is different, but the lateral forces on the structure are the same whether they are generated by ground movement/inertia (seismic) or wind blowing sideways on railings, posts, beams and joists. In the final sense of how the deck wants to move, physics doesn't care, they're the same.

As far as people moving a deck, it has to be a lot of people doing the Harlem Shake on a relatively undersized deck. It can be done, but is less of an issue. I guess I'd agree that this is more of a hypothetical situation unless the deck is being used as a dance studio. (The picture of the students doing the electric slide is in this link: http://www.deckmagazine.com/codes-an...-for-2015.aspx)

2. "In any case hacks don't follow any of the codes, whether the codes are strong or weak, so..."

Yeah, that's a good point. I'd like to see all the hacks put out of business, but that requires regulation, enforcement, and a cultural shift among the "no snitching" proponents in building. But it is indeed a valid point in terms of general public safety.

3. (a) "Not needed outside seismic zones; (b) not proven it's the only way"

(a) I disagree. While the need is more obvious in seismic zones, the need is absolutely there in high wind zones. What's the max. wind load you have to design for in your area?

(b) I'm all ears if someone has an easier way to do it. I can think of other ways, but they're not easier or cheaper. What do you propose?

4. (a) "It is arbitrary to have a set number of hold-downs when the deck size isn't addressed at all" and (b) "...I should not have to tear up the dining room floor and nail in a bunch of blocking just to install a tension tie."

(a) It's a lot like a shear wall. You put one hold-down at either end, regardless of the dimensions of the wall. You do have a point though, in that the load will be different depending on the size and proportions. But the number and location doesn't change, just the size of the HD. I guess be glad they're not making you put HDU8's in...

(b) If the cost of the flooring is too much, get an engineer to stamp the A35 to subfloor detail, and go through the ceiling. We do it all the time.

Of all the issues, I think the "hacks don't obey codes anyway" one is the most valid.

kevin

[HardleyWorkin]

Thanks for taking the time to explain your thinking, Kevin. Obviously I need to learn some more.

[kfc510]

Thanks for taking the time to explain your thinking, Kevin. Obviously I need to learn some more.

Hey, I'm not an engineer, take it with a grain of salt. That's just how I look at it.

And, I'll say this- it's a heck of a lot easier for me to tell the client "we have to" put the hold-downs in in e.q. country. I can imagine in other places HO's might say "my neighbor's guy didn't do any of that, I'm not going to pay for it.." (Not that that doesn't happen here too, of course, just not as often.)

Weird that I posted the link to the students rocking the boat (deck) at the Washington State lab and then this collapse happened recently:
http://www.wcsh6.com/news/national/a...-deck-collapse

Hard to say what happened there- there are reports of supports breaking, but it also looks like a section of ledger pulled off the house too. And I don't see any joist hangers on the section of ledger that remained.

kevin