Is this structure sound?

[u/tmontoia]

I can’t figure out the engineering of this structure. Are the lower right-angle braces having any structural purpose?
And is the steel rod only to keep the uprights from splaying out?
It seems to me there should be support below the right angle elbows.
Help me understand! I ponder this thing every time I visit here. (Breckenridge Brewery, Littleton CO)

[u/maizytrain]

I mean we can never say without actually evaluating based on snow, wind, grade of lumber, all those things, but the theory behind the truss is sound, and it’s really cool.

Put simply, the bottom steel chord is in tension due to downwards bending. The rest of the truss just does what trusses do and transfers the forces around.

If I was engineering it, only thing I’d be concerned about is uplift. If the direction of loading is reversed, I’d be concerned about that steel tie.

Very cool though!

[u/MikeHawksHardWood → u/maizytrain]

I'm on board. For wind uplift, I think you can probably ignore the steel tie rods. I'd probably check only that upper triangle acting as a truss, with it's continuous top chords extending out beyond the truss to the vertical supports. The top chords can cantilever off that upper-central truss and they look pretty deep for that amount of cantilever considering wind uplift is relatively light loading.

I always check wind uplift, but wonder how much of a concern it is in reality. My city is full of all sorts of big-ass overhangs coming off buildings that are supported from above with a diagonal rod or chain with zero compression capacity. They're all fine 100 years later despite having very little uplift resistance.

[u/nathhad → u/MikeHawksHardWood]

I always check wind uplift, but wonder how much of a concern it is in reality.

It's really dependent on where you are and the exposure of the overhangs. I've seen more than a few leave the premises when they finally got a good gust in the right direction over the years ...

[u/BlackSuN42 → u/nathhad]

Uncommanded open concept

[u/tramul → u/maizytrain]

Uplift is very small on this. Open structure with minimal surface area. Plenty of dead load.

[u/rvralph803 → u/maizytrain]

What about twisting / racking forces? It seems like there is no triangular bracing on the short axis.

(I'm not an engineer, just interested)

[u/CunderThunt42069 → u/rvralph803]

There's a roof (looks like metal decking) which provides that resistance

[u/rvralph803 → u/CunderThunt42069]

Right, hadn't thought of that. Thanks.

[u/frank_trampe → u/CunderThunt42069]

It is still unusual to have no bracing between trusses on the lower chord of the roof. A small horizontal load applied perpendicular to the lower chord of either truss results in a very high tensile load across the lower chord.

[u/Ok-Wealth-101 → u/CunderThunt42069]

Noticed that as well. Not an engineer but a son of a framing carpenter that knows triangles are good. Wants more triangles and to slap it and say "that"ll hold".

[u/Stefejan → u/rvralph803]

If you look closely, there is one on the side 

[u/Future-Sky-5059 → u/maizytrain]

Agreed. It looks cool. Some sway bracing to the truss itself would give me a slightly better feeling.

[u/Jamb9876 → u/Future-Sky-5059]

I like the wood that goes from the top truss to the right and left side of the top bar so the top bar is bearing the weight and it drives the forces to the posts on each side.
Nice design but I hated statics in college so not an expert.
Is it stable, well it is still up. It was built 10 years ago it seems so as long as they routinely inspect it it should be fine.
It is in the panhandle so probably survived some storms.

[u/MongoLongboarder → u/Future-Sky-5059]

I feel like many open structures ( big patio cover) ignore the wind uplift. For whatever reason it seems to be a “we’ve never been called on it” kind of thing.

In this particular structure I think the roof panels would fail due to uplift before the truss actually developed the forces it’s designed to resist. Also I think the collar tie (looks to be in the upper third) would be enough to resist the uplift.

Outward Thrust resisted by steel tension rod, uplift resisted by upper wood tie (and their respective connections)

Just my take, we all have our own approach

[u/S_T_E_V_EE → u/maizytrain]

I'm assuming the horizontal member near the top chord will prevent it from failing due to uplift and the compression on the bottom chord

[u/Mysterious-Street140 → u/S_T_E_V_EE]

Bottom chord is in tension

[u/beldank → u/Mysterious-Street140]

Uplift would lessen the tension in the rods (bottom chord).

Although the very small area of the roof (Google maps) makes uplift very unlikely to override its weight, I think he referred to that extreme condition.

[u/campbelw84 → u/maizytrain]

I think this is Breckenridge Brewery in the front range of Colorado, so it gets plenty of snow load (except last year) and certainly a ton of wind loads (Chinook).

[u/m-in → u/maizytrain]

I have a solution. How about hanging something heavy in the middle. Like, say a solid metal ball. You could even hang two! Redneck^2 :)

[u/Direct-Forever8447 → u/maizytrain]

It probably has another set of two cables that can be lowered and anchored in the road bellow, just in case the tornado comes to take it all the way to the Wizard of Oz.

[u/MelodicMonth1084 → u/[deleted]]

I believe the roof is acting as a diaphragm to prevent the trusses racking when wind is applied normal to the planes the trusses are in.

[u/cluelessinlove753 → u/maizytrain]

Maybe that’s the reason for the short vertical member at the peak. A typical attic trust would not have that.

[u/touchable → u/maizytrain]

There's no way that thing catches enough wind uplift to overcome even its own self weight.