Knee brace alternative for truss racking

[Ecreps]

Hello all,

I recently got my building permit back for a pole building I'm hoping to start on in the next month or so. It all seems pretty normal with one exception.

They require knee braces (48" at a 45 deg angle) between the poles and the trusses. They say this is necessary to prevent truss racking. Are these needed? are there alternatives? From what I am reading they are largely ineffective; because the trusses are not designed to be loaded where they attach. Any experiences or thoughts are appreciated.

I am hoping to finish the inside once it is built, and these will make that more difficult to do.

Thank You.

 

[ace10]

Are the braces on the drawings from the truss company, or is this something the building department is calling for?


Who is the "they" in your post?

 

[Ecreps]

Are the braces on the drawings from the truss company, or is this something the building department is calling for?


Who is the "they" in your post?

The builder/engineer for the pole barn company did not have any knee braces; they do not typically use any.

The county building permit is calling for them to eliminate truss racking.

 

[ace10]

Well that's easy.... comply with the county's requirement, and then remove the braces when the bureaucrats have finished snooping around.

Use screws to make it even less painful to revert back.

$0.02

 

[zkdiesel]

They will make your building significantly stronger! Have watched them save buildings with them be without side by side in huge wind damage areas.

To tin around them for inside, just leave them protrude through your tin or drywall. Then you can wrap them for the wood look.

 

[Cypress]

Well that's easy.... comply with the county's requirement, and then remove the braces when the bureaucrats have finished snooping around.

Use screws to make it even less painful to revert back.

$0.02

This. If it’s not called out on the struct dwgs, they are not needed for support and quite silly for the county to even have such requirements.

 

[WNYflyer]

This. If it’s not called out on the struct dwgs, they are not needed for support and quite silly for the county to even have such requirements.

^ This,

If they are not shown on the sealed issued for construction drawings then they are not required and could actually be detrimental to the structure since they are not part of the engineer of record's assumptions and thus his design.

 

[theoldwizard1]

The builder/engineer for the pole barn company did not have any knee braces; they do not typically use any.

The county building permit is calling for them to eliminate truss racking.

This is a classic "you can't fight city hall".

The real issue is how are the roof support beams connected to the posts and how are the truss connected to the posts.

 

[mobetta]

they dont even have the right nomenclature
Id like to see a truss rack that way.
now it could prevent the whole building from racking but the design of how the bits are attached together usually would prevent this.

Do you have a set of Stamped Engineered plans?
In my experience that is enough to get the city/county officials off your back- if an engineer stamped the plan HE is taking responsibility for the design, relieving the AHJ of liabilities....

It is possible the human you are dealing with at the county has no idea and a friendly conversation with a supervisor may resolve this.

 

[kbs2244]

In case of damage your insurance co is going to notice any deviation from "as inspected"

 

[firebirdparts]

Your insurance company would have to have ESP and hidden cameras in your shop to do a thing like that.

 

[theoldwizard1]

In case of damage your insurance co is going to notice any deviation from "as inspected"

Wrong term. Insurance wants it built "as drawn".

 

[Marctrees]

Related to this... I speced my gable end posts to get cutoff flush with the tops of the 4/12 truss top chords.

I don't know how much but that cetainly should help at least on a smaller like my 1300 ft sq building.

So the posts strengthen trusses 90 degrees to the OP's knee braces.

The knee braces in OP post would do nothing for truss bracing, but of course wall to roof bracing.

Trusses are usually braced parallel to ridge direction.

Marc

 

[Ecreps]

Thanks for the replies everyone. As weird as this may sound; there is no building inspection. I think I will just have them put on with screws for the moment; if I can't find a good way around them I will just remove them at that point.

The trusses are specced for the proper wind loading (115mph) without them. I called the county and was told it was to resist the building racking in line with the trusses during heavy wind loading and that the post embedment would not be sufficient to resist this.

This seems odd to me; 59" of post embedment on a 30x40x14 building seems deeper than average from what I have seen. I believe this is possibly a case of the county engineer just applying a blanket fix across all buildings whether they are 30x40x14 or 100x200x30.

 

[Firebrick43]

Around here they like to see the ends sheathed in osb to stiffen them up especially if the side is exposed to west winds here on the prairie or the end doors are excessively big.

 

[Ben W]

Around here they like to see the ends sheathed in osb to stiffen them up.....

This is how you deal with a lateral load. Your roof acts as a rigid diaphragm (or beam on its side) translating the wind loads over to the end walls. The end walls carry the load to the foundation. And alternatively if the wind blows in a 90deg orientation (say from the south rather than the west), then the side walls carry the load with the roof still acting as the diaphragm.

The post embedment depth is beneficial, but not significant compared to the wall sheathing/metal skin.

The truss fabricator may take exception to you installing this 45deg bracing. Those bottom chords are typically meant to take axial loads only, so introducing a brace at a random point midway on the 2x6(or whatever) is not what it's been designed for.

You see this bracing done fairly often and so for some builders/inspectors it's translated to a standard.

 

[PWilks]

^ This,

If they are not shown on the sealed issued for construction drawings then they are not required and could actually be detrimental to the structure since they are not part of the engineer of record's assumptions and thus his design.

Hate to break it to ya, but over-constraining something that’s not supposed to move to begin with, I.e a structure, will never be “detrimental” to a structures design, especially when you’re talking about constraining lateral movement of something that doesn’t move laterally anyway.

 

[Ben W]

The structure as a whole won't be hurt by providing additional bracing capacity (i.e. 3-plys of sheathing when only one is needed for example), but the trusses themselves may. The bottom chord of the trusses may not be able to handle an imposed bending force midway between nodes (where the splices happen). When the wind blows and the brace pushes against the bottom chord (2x4 or 2x6) you're asking it to resist bending as well as the axial tension it's designed for.

Practically, if the building is appropriately designed for wind, then it's unlikely the trusses are going to fail because the building has already been engineered to not move. The braces only exert a force once the building starts to rack.

Say the worst happens and the building is laying on the ground ... then the truss fabricator sees these braces which he didn't know were to be installed? Pretty easy for him to say you didn't install the trusses per our requirements.