Outdoor Patio Tie Rod Connections

[Civ-StructEIT]

I just got tasked with looking over and reviewing a patio design from a Landscape Architect. It is a pretty simple setup, where there are 4 6x6 timber posts (10.5' high) spaced 20.5' x 23.5'. There is no roofing for this patio, but the architect is proposing 1/2" steel tie rods connecting to each of the timber posts at 9.5'. The tie rods would then be supporting various light fixtures. This seems sketchy to me, but I wanted to check to see if this is something anyone else has seen and worked well before, or if there was a good alternative to look at. Thanks!

 

[KootK]

Well I certainly didn't mean to imply that the the cable provided a pinned, lateral support to the top of the post. Hopefully that's not what the OP intended either.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Civ-StructEIT]

Haha. I apologize that I was not clear with my last post, I am obviously aware that the cables do not provide any support at the top of the post.

The location of this "patio" is a fairly high end winery, so the aesthetics are very important. I do agree that the wood column and cable design would be the way to go, I am just struggling to find something that looks good and I am comfortable with. After a handful of iterations, I have found that a 6x6 Douglas Fir - Larch, Select Structural grade post just passes my checks, with not much room for error.

 

[KootK]

I was sorely tempted to just recommend "6x6 and let 'er be". I just didn't want to get cavalier-shamed. KootK approved.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[jdgengineer]

If this is high end winery I change my answer to steel post 100%

 

[XR250]

yea, steel post for sure or maybe an 8x8 wood post. Anything else will ultimately have visible creep.

 

[dhengr]

Civ-StructEIT:
The Arch. draws cute and sexy sketches, he just doesn’t have the vaguest idea what he is doing or what he is asking for. Sure, it can be done, but probably not with a 6x6 wooden post with some undefined connection and foundation at the base. He might even be able to point to some similar patio structures which are still standing. They just aren’t very old, haven’t likely seen full design loads, winds, ice, etc., or been used as chinning bars by some drunk, as mentioned above. They haven’t seen much weathering, aging, creep, long term deflection, etc. I’ve also seen some of these which, when you leaned on one post, you could see the top of the whole structure move laterally. I don’t like the large lateral loads induced at the upper tips of those posts, those will be an ongoing problem and an aging problem. I’d be inclined to use a light stl. 4x4 HSS, and then clad it in 1x6 wood for a finish, with a water shedding cap, bottom drainage and some venting features. Painted all sides before final assembly and final outer painting or staining. I’ll bet that at some point, they will want a fabric tent/sun screen over the top of this structure. The 8x8 HSS base detail is very complicated for what is does; placement, conc. forming, etc. What happens when this fills with water and frezzes?

I would take the approx. shape/arrangement that the Arch. shows on his elevation for the horiz. spanning members (20.5' and 23.5' lengths), if he is really set on that general shape, but rework it as follows. I would want these to act like light trusses, with a real top and bottom chord, with some diagonals (?), maybe just wrought iron infill, like a wrought iron fence or gate, maybe not as well defined or symmetrical as a std. OWSJ, but a truss nonetheless. The ends might have some lower wrought iron brackets below the bot. chord and finally end plates, 3"-4" wide, 1.5'-2' high bolted to the posts. These trusses carry some gravity load, and hold the posts together in tension or compression. The cable or tie rods aren’t required any longer so the large tip lateral load goes away. Some extra tube or some such, his scalloped shape, might be fixed below the bot. chord to act as conduit and base for the light fixtures. I would probably install a couple diag. cables and turnbuckles from corner to corner, for some stability.

 

[KootK]

You could go the other way and try to out-architect your architect. There would be stuff to consider, of course, including your fee. And architects never seem to find my cool ideas as cool as their own.

Maybe some cable bracing in the middle two panels. One would have to let the numbers be their guide.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[XR250]

KootK, I think your patron is going to get crushed due to an LTB failure.

 

[KootK]

Oh contraire, I think that she'll savour her gluten free salad and pumpkin spiced chi latte in peace. Vertical rods in combination with weighted/taught lower cable should stabilize the whole thing against LTB rotation if properly designed. It's the load that's gotta roll closer to the ground, not the top chord. At least that's it with a truss assumed weightless-ish.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[XR250]

Aaah, did not catch the cont. vertical rods - clever.

 

[KootK]

It seems that I neglected to mention that the verticals would be continuous. It must be inferred by zooming in very closely and observing subtle graphical cues.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.