SDS screws to built up column around windows in tall wall 2

[pdev67]

Hi There, just curious to know

In 18' tall wall 2x6, 2 king stud and one cripple stud as a built up column (3ply) fastened with sds screw staggered at 24"oc but screw get inclined as there was not enough space to drill, how much strength will reduce or should add one more screw in between to make spacing 12" oc

 

[jayrod12]

How much of an incline? Are you getting adequate penetration in the third ply?

 

[KootK]

1) For this kind of application, I believe that the primary purpose of the fasteners is to prevent relative, longitudinal slip between the plies. Given that, an inclined screw is probably better than one with no incline as an inclined screw would offer more stiffness to resist such slip.

2) As jayrod12 intimated, it's all for nothing if the screw doesn't actually penetrate all plies sufficiently.

3) The screws perform a load sharing function for transverse loads but I'd not expect that aspect of performance to be compromised by the inclined screws. With or without the incline, you've got some dowel action.

4) There would be a "right way" to orient inclined screws as shown below. That said, I've no doubt that this is not how it was done in the field and for an application that is primarily about buckling, I don't feel that it's terribly important.

5) If you're in doubt at all, go ahead and add some extra screws, perhaps reversing the incline.

 

[msquared48]

Screw the screws. Just use a Glulam. KISS!

For an 18 foot span, I would be concerned with deflection with only a 6” depth.

Mike McCann, PE, SE (WA, HI)

 

[pdev67]

Thank you so much All,
Jayrod12, it's is 5" long inserted at an angle of 30 degree, so for three ply 2x6, full depth insertion at 30 degree should be 4.5"/cos30=5.196
kootk, thanks for explanation

 

[Mike Mike]

pdev, Is sheathing attached to studs to prevent weak axis buckling? Has the (1) 2x6 trimmer been designed to resist the entire vertical load? If so, little to no fastening is needed from a mechanics standpoint (although you still need them from a code compliance standpoint).

One might argue fasteners are needed to transfer lateral loads acting out of plane on your wall opening from your trimmer into your king studs, but one might counter this load can go from your trimmer into your sheathing into your king studs, avoiding the need to attach trimmer to kings.

 

[pdev67]

Thank you Mike, yes sheathing attached form exterior and trimmer was designed for the vertical load

 

[dik]

and glue... I'm not sure, but should the screws be loaded in tension or compression? just curious...

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

-Dik

 

[Mike Mike]

Screws are best in tension. Typically the compression load path is directly from wood member to wood member so it's not typically possible to load screws in compression.

Yes glues works, although structural engineers don't typically count on it for calculation purposes. At the risk of starting a tangent, has anyone ever prescribed or even seen a "structural glue"?

 

[jayrod12]

There are structural grade adhesives, but the requirements for installation are so tight that generally wouldn't believe it can be done in the field with any sort of confidence. Generally the application temperature and pressure required make field applications unfeasible.

However, that being said, PL Premium certainly does get a ton of hold, just hard to quantify.

Lastly, If I ever asked a contractor to glue together stud packs at window jambs or under point loads, I'd likely never be asked by that contractor to do work for them again. I'm impressed with only a 3 pack stud pack that you even required SDS screws. Usually it's just nails around here, 2 rows of 3" nails @ 6" o/c.

 

[pdev67]

Thank you Mike Mike, Jayrod12- just curios to know, is there any minimum number stud pack for SDS screw? or up to how many stud pack, nails are good

 

[jayrod12]

Well the CSA O86 (Canadian wood standard) allows for up to 4 ply stud packs to be nailed. Once you get to 5 ply they indicate they should be bolted, or else you have to take a strength reduction into account.

I don't know what the NDS says if you are in the US.

 

[Mike Mike]

Which country are you in? NDS doesn't limit plies for nailed applications. It does say in 15.3 if the column is designed as a "built-up" member instead of as individual plies, each nail must penetrate all plies, but this doesn't apply here since pdev's (1) 2x6 trimmer alone is sufficient and fastened to sheathing. So I would say no, there is no limit to the number of plies that can be nailed instead of screwed or bolted in the US.

 

[KootK]

...this doesn't apply here since pdev's (1) 2x6 trimmer alone is sufficient and fastened to sheathing.

I get what you're saying and have made similar arguments in the past myself. That said, I feel that it should be mentioned that:

1) The jack studs actually rely on the king studs for their stability. So I don't believe that it is entirely correct to say that we don't have to worry about the king studs because the jack studs calculate out by themselves.

2) Fastening to sheathing only works for buckling if both exterior plies are fastened to the sheathing such that the plies in between are laterally contained. I'm not sure that can be assumed with conventional nailing patters.

3) Fastening to sheathing only works for load distribution if:

a) The nails, loaded in withdrawal, can resist the forces delivered and;

a) The sheathing, acting in bending and shear, can resist the forces delivered.

In both respects, I would expect demand to be much higher than that required for a typical field nailing condition. That, particularly given that the loads coming from the opening side are likley to be delivered as concentrated loads at the header and low sill.

This is all a bit pedantic, I admit, but real none the less.

 

[Mike Mike]

Thanks for the thoughts KootK.
1) The jack stud always has to be fastened to sheathing since it's on the edge of the panel. Are you saying fastening the jack stud to sheathing alone doesn't provide enough stability?
2) Yes, each ply either needs to attach to sheathing or attach to another ply. No free-loading around in the wall cavity. In the US I have seen nailing patterns both ways: some attach sheathing to every ply, some only to the jack stud. What are you used to seeing?
3) Agreed, especially if pdev attached his sheathing with nails, and especially if his tall wall has a monster window in it like it probably does. Even without considering load concentrations, the wind load to transfer from jack to kings for a 10' window might be 100plf. 8d commons at 6" oc can only take about 70plf in withdrawal.

 

[KootK]

Thanks for the thoughts KootK.

Well... that's awfully genteel of you. Thanks for entertaining my thoughts.

1) The jack stud always has to be fastened to sheathing since it's on the edge of the panel.

I'd failed to consider that. I see your point.

What are you used to seeing?

I'm ashamed to say that I've never looked. I'll make a point to in the future. Certainly, were I to count on this, I'd want to ensure that I specified it in my drawings someplace.

I suppose that I've always had a visceral mistrust of bracing anything other than a field stud with sheathing. And that may just be a me thing. I remember being horrified when I discovered that you can one-side drywall sheath a party stud and call that braced.

This is to delve into the muck of engineering philosophy but it seems to me that most of us claim to have some sort of structural engineering "intuition" that informs our opinions about what's right and wrong. Trouble is, most of our intuitions seem to be based on nothing other than having done some real conservative stuff in the past and having that not caused problems for us. It's not as though my uncle is a retired partition wall stud and I can just ask him what it felt like to be one. Testing and established dogma kind of have to be king for lack of better alternatives, regardless of how I "feel".

 

[KootK]

Yessss... I found the old thread that formed some of my opinions on this: Link. You can see that I've been flip-flopping on this for a while now like a politician.

 

[Mike Mike]

Thanks for the link KootK. Your forensics article link no longer works but it looks like a good read from what you pasted in there.
Structural drawings do typically need to be more explicit about sheathing fastening requirements at multi-ply members, but they're usually too busy vaguely specifying bigger picture items. My folks are ex studs. They said they were all stressed out all the time.

 

[KootK]

Here's an updated link to that forensics article if anyone is curious to check it out: Link. Nothing earth shattering: sometimes the the nailing isn't perfect.

 

[SwinnyGG]

has anyone ever prescribed or even seen a "structural glue"

Is there an experienced structural engineer here who has never specified epoxy anchors/dowels?