What counts as torsional restraint for wood design 1

[CollinW]

Hello, this has been a discussion between some at my office and I wanted to get some additional opinions because we decided we don't know. NDS Section 3.3.3.4 states "where the depth of a bending member exceeds its breadth, d > b, lateral support shall be provided at points of bearing to prevent rotation," but what do you typically consider to satisfy this? Typically for new construction we ask for full depth blocking for everything, but this is existing.

Attached are two images that are in the field and have existed for a while and I would like to get some additional opinions if you would be comfortable signing off on this. Both mostly support live load and very little horizontal load.

The first one is blocking equal to half the depth of the beam. The beams are 4x12s and span about 20'.

The second one is (2) toenails on a 2x6 wood beam. The span is about 4'.

Any additional references that you could point me towards would be of great help. Thanks.
Edited: Fixed typos

 

[ChorasDen]

Image put in-line.

 

[ChorasDen]

I'll try and address the general notes published within the NDS later when I have more time, but I would first suggest looking at the loading/spans vs. torsional restraint requirements per 3.3.3.4 for your half depth blocking detail. 4x12 doesn't generally have a large moment capacity relatively speaking, and thus, it's probably that the material dimensions are such that lateral restraint is not required. I bet the commentary to C3.3.3 has some useful information for you, if you have a paper copy that you are able to access.

 

[BAretired]

In the NDS it states "where the depth of a bending member exceeds its breadth, d > b, lateral support shall be provided at points of bearing [highlight orange]to provide rotation[/highlight]," but what do you typically consider to satisfy this?

Shouldn't that be "to prevent rotation"?

I would not trust toenails to prevent twisting, but it really is a matter of engineering judgment. If you suspect a beam is not adequately braced against torsion, add a block or brace to ensure it stays put.

 

[CollinW]

Ok, we will request for them to add blocking for the cases with toenails, but not comment on the half depth blocking. The only thing that the NDS commentary added was if the compression flange is continuously braced, which I do not believe applies because the planks could just go along for the ride. Thanks!

 

[XR250]

You are concerned about the bottom of the member translating sideways at the bearing?
I would not worry about it. Never seen a failure like that.

 

[lexpatrie]

I'm not convinced anything you're specifically mentioning here provides restraint against twist. For joist hangers, there's a twist strength requirement I don't recall, but it does exist, so adding face mount hangers if you didn't like it is an option or another option.

Usually I think most engineers would consider the plank as a source of top flange restraint along the full length. And usually there's more than the plank, you'll more often (in my opinion) see diagonal planks which probably feels more like a restraint, but most of these floor systems the plank is there but there's also sheathing/subfloor above it. The combination probably provides enough restraint for some engineers, if not all.

Are we talking 30 psf live load residential, 40 psf residential, 100 psf assembly areas?

To broaden the discussion, the floor joists sitting on a ledger are supposed to have concentrated nailing beneath the joist (as I recall), not distributed nailing for the ledger, and these details have limited strength.

Ledger Strips and the Code, Woeste, Loferski, Journal of Light Construction, Nov 12, 2020

 

[CollinW]

The ledger strips JLC article was a good read, thanks. The concern is more the top of the beams translating sideways because the planks are not continuous and typically only span 1-2 bays with nothing else that they frame into. This is a catwalk with 30 psf LL.

 

[lexpatrie]

ESR 1539, International Staple and Nail Association, Revised April 2024, has some nice figures -

It shows the nailing at the ledger, and it also shows nailing into the joist through the rim board (See IBC Connection 29 and 30). You probably don't have access to nail into the end of the joist through the supporting element, but the "torsional" capacity of that element could be calculated to provide an equivalent. I think the flooring is more effective at restraining twist than you think.

2021 SDPWS Chapter 4 does provide values for horizontally sheathed planks for walls and floors. See Table 4.2D.