interior truss heel sheathing

[struct_eeyore]

I have a series of wood trusses terminating on the interior of the building which have some very tall heels (13'+)
There is no shear transfer by design here - although some might occur in reality.
I'm leaning towards sheathing this section full height, but am wondering if that might be overkill - in lieu of X-bracing.
(truss profile is hatched in figure below)

 

[KootK]

I do feel that is overkill if there is no explicitly need for shear transfer at the interior location. Sheathing that for sport may perceived as incurring meaningful expense needlessly. Unless I misunderstand the situation, all you need there is the end vertical bracing at the locations specified by the truss manufacturer.

 

[Flotsam7018]

I definitely get concerned with adequate rollover restraint and keeping the end vertical plumb in situations like this. So I don’t find it overkill, especially since I’ve seen a lot of truss bracing missed or not installed properly. I have specified truss panels between trusses at an interior bearing with tall heels like this like you’d do for a shear wall, sheathing is likely easier but if you’ve got trusses coming in from both sides the panels become the most practical option I have found.

 

[JAE]

If you don't need the sheathing to transfer lateral loads to a shear wall below - the only reason to do it would be temporary during construction.
Once all the roof sheathing is in place, the "whole" of the roof system would probably be quite stable - assuming a hip type roof perhaps.

 

[KootK]

I definitely get concerned with adequate rollover restraint and keeping the end vertical plumb in situations like this.

Similar to @JAE, I don't see a rollover demand here other than in the erection condition. I see the top chord of the truss being laterally restrained by the roof diaphragm and the bottom chord being laterally restrained by the supporting wall and / or ceiling diaphragm. Add those two together, and would think that you have very effective rollover restraint. That said, I have seen some situations where I've had so little confidence in the diaphragm detailing that have questioned the issue of rotational restraint.

 

[Flotsam7018]

Heck, I block floor joists at an interior bearing for rotational restraint, I’m definitely going to do that for an extremely slender truss web and not rely on the roof sheathing and toenails at the top plate. Any out of straightness/plumb or secondary effects of the web wouldn’t be addressed either.

Perhaps I’m jaded as I’ve seen an end web buckle about 2” along the weak axis in this exact scenario.

 

[KootK]

I’m definitely going to do that for an extremely slender truss web

I believe that you are speaking to a K=1-sh buckling of the truss web rather than a wholesale rollover of the truss. Those are different things in my mind. The former can be addressed by as little as a line or two of horizontal strapping that hits an x-brace once in a while. Similar to OWSJ bottom chord bracing.

Heck, I block floor joists at an interior bearing for rotational restraint

I see your point to an extent. However, I would argue that:

1) There are several reasons for such blocking of which rotational restraint is only one.

2) I doubt that rotational restraint is required in the complete system in many cases. Certainly, I've seen a whole lot of 2x10 lapped bearing conditions without blocking that have preformed just fine.

3) Such rotation restraint is deemed worthwhile because the joists are so shallow. On a typical roof truss end, you're lever arm between the diaphragm and wall lateral restraints is going to be functionally enormous.

 

[RontheRedneck]

I you do use X-bracing, be sure to allow for the CLB(s) that will be required on that tall web.

 

[Greenalleycat]

I think you're completely right to do 'something' but how much is required will depend on whether there is a design intent (lateral load transfer?) or just trying to prevent incidental loading
I think both X-bracing or sheathing would be fine - I've used both in my own similar designs
You could even just block at top and mid height of each web panel then put internal sheathing at say every 3rd or 4th truss bay to give some nominal stability

 

[Flotsam7018]

Certainly, I've seen a whole lot of 2x10 lapped bearing conditions without blocking that have preformed just fine.

Agreed. However, I'd be much less concerned with a 2x10 without rotational restraint than a 13ft truss heel. Any incidental horizontal loads would be relying on the truss plates at the chords to transfer out of plane moment or for the chords to resist rotation. A 2x10 doesn't haven't any potential hinge points, though I still provide blocking there as well - in part because the NDS tells me I have to, but also for the many functions it often serves as you mentioned. Also - just makes me feel good, so that's got to be worth something!

I could get on board with the CLB strapping for the webs with diagonals that tied into blocking between the top/bottom chords. There's many ways to get the job done, but as Greenalleycat said - I would do something. I still standby that it is not overkill to provide rotational restraint here. Is it absolutely necessary in a world where everything is perfect, probably not - but I don't live in that world.

 

[KootK]

Any incidental horizontal loads would be relying on the truss plates at the chords to transfer out of plane moment or for the chords to resist rotation.

Hell no. All that needs to happen is that the bottom chord receive lateral (not rotational) restraint at the top plates. And this basically just turns into an in plane shear demand on the wall which the gyp sheathing will be able to deal with handily.

However, I'd be much less concerned with a 2x10 without rotational restraint than a 13ft truss heel.

I see it the exact opposite because of the lever arm distance between the points of lateral restraint for the two different situations.

For OP's truss, the lever arm is a whopping thirteen feet! So the lateral restraint at the top and bottom of the truss will need to be neither stiff nor strong to be effective. From a stability standpoint, this is a complete slam dunk.

Conversely, the lever arm on a 2x10 is only 9.5". So the quality of the lateral restraint must be both stronger and stiffer.

A 2x10 doesn't haven't any potential hinge points

It has the exact same rollover hinge point that the truss has: the bearing point on the wall.

 

[KootK]

how much is required will depend on whether there is a design intent (lateral load transfer?)

No lateral load transfer per the OP.

There is no shear transfer by design here - although some might occur in reality.

And, really, one of the best ways to avoid that unintended shear transfer is... to not sheath the truss ends. Once you brace that, it will draw shear.

 

[RontheRedneck]

Also - just makes me feel good, so that's got to be worth something!

Forcing someone to spend thousand of dollars to install plywood just to make you feel good is not reasonable.

I could get on board with the CLB strapping for the webs with diagonals that tied into blocking between the top/bottom chords.

The CLBs are supposed to be braced with diagonals anyway. So that wouldn't add much cost.

 

[Flotsam7018]

Ron: That was just for some levity, I completely agree about not adding cost without justification. That’s why I’m spending the time to hash this out.

KootK: The horizontal force I’m discussing would be a result of some angle between the web and the chords. I’m getting the impression you’re imagining everything in the truss remains planar.

 

[KootK]

I’m getting the impression you’re imagining everything in the truss remains planar.

No, I acknowledge tolerance in all things but, yeah, trusses do tend to be quite planar. I've built enough of them to know.

The horizontal force I’m discussing would be a result of some angle between the web and the chords.

Like this??

 

[KootK]

Forcing someone to spend thousand of dollars to install plywood just to make you feel good is not reasonable.

I support engineers doing whatever it takes to make themselves feel good with respect to public safety. The buck stops PE's and, unfortunately, a great many things in most buildings are not clear cut from a design necessity perspective.

I definitely consider the sheathing to be wasteful here. But, then, that's based on my own understanding of what is important here, not @Flotsam7018's. While I would love to convince @Flotsam7018 to see this my way, if he's not convinced, then I wholly support his keeping on doing what he's been doing.

 

[RWW0002]

Considering a similar condition of a long-span truss with an interior bearing wall (where sheathing is not possible). Are you thinking trusses need to be blocked for stability (again not considering shear transfer - lets say this bearing wall is not a shear wall). This leads to some crazy-looking blocking details (13' tall+ x 2' wide blocking panels or shear frames with no significant load transfer..)

Or do you see this one as a different case because there is no blocking at one end of the truss??

 

[KootK]

Or do you see this one as a different case because there is no blocking at one end of the truss??

I see it as a different case simply because the origin of the demand is very different. With a long span truss continuous over an interior support, you have a mission critical need for compression bracing of the bottom chord over a significant length of that chord, not just at the bearing wall.

So my first stop on my way to Overkillville would be to ask myself if this remains a situation where I am comfortable allowing the ceiling sheathing to do the job of compression bracing the bottom chord. If the answer is yes, then I don't see that anything needs to be done at the bearing wall. If the answer is no, then it becomes a situation that you probably need to address at more locations than just the bearing wall.

This leads to some crazy-looking blocking details (13' tall+ x 2' wide blocking panels or shear frames with no significant load transfer..)

Yeah, that would be ridiculous. Both costly and not especially effective.

If you will be dealing with a repeating truss profile, one decent option for BC bracing is shown below. Loose pieces assembled on site. Force the existence of a web in the same location in each truss where the braced lines will be. Within reason, one can brace compression chords by bracing the incoming webs.

 

[RWW0002]

KootK - agree with you on all points. I think bracing of some sort for the interior bearing case is both more critical than the case proposed above, and less likely than the above case to have a blocking bracing or sheathing solution proposed by most engineers (just due to how common a condition it is), which is why I brought it up.

Thanks for the sketches and critical thought all. I am following along with this one (without contribution much) just like I do on most threads around here.. Ha!

 

[RontheRedneck]

Ron: That was just for some levity,

Sorry that I didn't catch that.