Deflection in Steel Channel? L Bolt Adequacy?

I am trying to determine feasibility of the following proposal.

A 3” x 7.1 lb A36 steel channel—12’ long—will be vertically embedded in a poured round concrete pier (15” diameter), so that 3.5’ will be embedded in the concrete and 8.5’ will be above the concrete. The portion embedded in the concrete will be tied to appropriate rebars.

A 1/2” diameter hole will be drilled through the channel web, 1” from the top. A 1/2” diameter 18-8 stainless L bolt will be inserted in the hole, with on each side a washer (2” outside diameter, 1/4” thick) and a nut.

A steel sculpture will be hung on the L bolt, with the load point being about 2” off the channel web. The sculpture weighs about 250 lbs.

Two questions:

Will there be visible deflection in the steel channel?

Does the L bolt appear adequate for the load?

Alternatively, I am considering using a 3” x 4.7 lb 304 stainless channel. (That appears to be the heaviest 3” stainless channel that is a stock item.) The alternative does not have the rigidity of the 3” x 7.1 lb A36 channel, but visually will work better in showing the sculpture.

Question: Will there be visible deflection in the stainless channel?

Thanx!

No deflection to the uncalibrated Mark One Eyeball of Joe Average .. not unless he gets on a ladder tall enough to sight down it, no. There ARE no "immovable" objects, after all. Not even whole galactic masses, and even a beam of light can be bent and DOES bend.

But, but... what d 'you suppose is the sculpture's aerodynamic profile, high winds? more important question is how much TWISTING moment it needs to endure?

thermite said:

...No deflection to the uncalibrated Mark One Eyeball of Joe Average...

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Well, I disagree. A 250 lb weight perched on the top end of a single 8-1/2 ft. length of 3" channel will move around
quite a bit. No so much if the thing is left undisturbed but if someone pushed on the middle of that channel the
top is gonna swing quite freely--I'm guessing 2" - 3" of easy movement; more if the pushing is substantial and
repeated. It's not going to break but it will move. I'd recommend a piece of 3" square tubing. It will have more
strength and it will be more aesthetically pleasing...

LKeithR said:

Well, I disagree. A 250 lb weight perched on the top end of a single 8-1/2 ft. length of 3" channel will move around
quite a bit. No so much if the thing is left undisturbed but if someone pushed on the middle of that channel the
top is gonna swing quite freely--I'm guessing 2" - 3" of easy movement; more if the pushing is substantial and
repeated. It's not going to break but it will move. I'd recommend a piece of 3" square tubing. It will have more
strength and it will be more aesthetically pleasing...

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He's only 2" off the surface - 3 1/2" to centerline. But could be.. I'm thinkin nearly flat panel, but we know not how THICK the sculpture, nor where its own CG be

How about bog-common Sched 80, 4" round, "red Iron" pre-primed, and top-coated to suit, then?

Want to get more "rigid", use heavy-wall "hydraulic" tubing ....drill steel.. or recycled tapered & galvanized highway traffic light support two or three lane capable.



More 'crete depth and width as well for one of THOSE cantilevered puppies!

Note- coat the steel with corrosion protection, preferably an epoxy paint, prior to installation.

thermite said:

...He's only 2" off the surface - 3 1/2" to centerline. But could be.. I'm thinkin nearly flat panel, but we know not how THICK the sculpture, nor where its own CG be...

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None of that really matters. It's 250 lbs. suspended just over 8 ft. above the concrete with no support. Of course
it will flex. Take a piece of channel (lying on the flat, of course) clamp it to a solid workbench with a little over 8 ft.
sticking out and put your weight on the end--see how much it moves. Consider the fact that,when pushed from the
side it will move that much off centre in both directions and you get the idea. If you synced your pushing action and
got some harmonics going I'll bet it would move even further...

It seems to me that a single channel is about the last thing you want.

If you want to use channel, weld two together. Or use a round, or pipe. Square tube maybe, pipe is stronger against twisting if the same size as the corner-to-corner measurement of the square tube, and has the same visual mass.

You might even get that channel to collapse if you "pumped" it like a swing, either in twisting, or maybe in the short direction of the channel.

Betcha you would never consider that if you had to support the load out horizontally, even at a much shorter length.

LKeithR said:

None of that really matters. It's 250 lbs. suspended just over 8 ft. above the concrete with no support. Of course
it will flex. Take a piece of channel (lying on the flat, of course) clamp it to a solid workbench with a little over 8 ft.
sticking out and put your weight on the end--see how much it moves.

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The OP has described an eccentric axial load. Not a lateral load like you have described.

That eccentric axial load will create both compression and bending stresses.

As mentioned up above, tube steel would be a better choice.

Doug W said:

The OP has described an eccentric axial load. Not a lateral load like you have described.

That eccentric axial load will create both compression and bending stresses.

As mentioned up above, tube steel would be a better choice.

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Also .. build it like a lantern post. Run the support rod across the centre of a tube or square, projecting out BOTH sides, not out the "front".

Or clamp or weld a crossbar to the BACK side of a channel.

Hang the sculpture with a PAIR of Ell brackets, "loop" bent or U-bolted. Secure it at the bottom against excessive excursions. Now the axial load is better balanced, vertically, and it's "dynamic" range of motion restricted.

See metal fencing. See "STOP" signs, et al.

The signs don't weight much. The wind loading is another story. Even so, simple rolled "U shaped" sheetmetal, round or square light tubing not that different from electrical conduit serves all over the planet.

If the sculpture is openwork? Yah STILL have wind gusts and twist to manage. Hence tube, rather than channel.

Openwork can also accumulate significant ICE loading if left in-place at wintertime.

Doug W said:

...The OP has described an eccentric axial load. Not a lateral load like you have described...

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I guess I should clarify a bit. My description of applying a lateral load to the channel was to illustrate the fact that, if a load is
applied, the channel will flex. If this piece of art is standing in a vacuum where no one ever touches it then the channel is more
than adequate for the job (although not the best choice from an appearance point of view). If, on the other hand, the piece sits
in the open in a public space you can almost guarantee that, at some point in time, a couple kids are going to see the possibilities
and start pushing on the channel. If they get it right they'll be able to et it oscillating pretty good. As I said before, it's not going
to break but it is going to move. Sometimes you've got to design things for the worst case scenario, not the best...

LKeithR said:

XXX Sometimes XXX ^^^ ALWAYS ^^^ you've got to design things for the worst case scenario, not the best...

Click to expand...

There. Fixed that for yah...

The OP BEING a sculptor, and having control over the concreting & re-bar tie-in, one might presume this is entry ramp signage or placed adjacent to the studio as a display - a possibly seasonal dynamic advert for his own shop and bizness?

AND NOT something in a public plaza, park, office or hotel atrium/lobby nor otherwise "open to all comers" low/no control shared leisure area?

2CW

And I still like round tube for the tasking.. "lift-out" socketed for swapping height to suit more than one sculpture, and even with a gusseted base receiver - mini-jib crane or traffic light style.

And/or LIGHTER sculptures?

I did say "worst case"?

Eng-Tips Engineering Forums is the place for YÜÜ....

I actually have installed several dozen weird heavy sculptures in all kinds of situations. And as I see it, you have several problems here-
First- you are too cheap to hire an engineer.
Where I live, you can generally find a certified structural engineer to look over your idea, and, assuming it doesnt require stamping, do the calcs for a few hundred bucks. If it requires a stamp, of course, it will be more, but still should be under $500 for this.
Since it could potentially fall, and possibly hurt someone, this is money well spent.

But beyond that, every thing you are describing is too wimpy.
3" channel is, as mentioned above, not symmetrical, and will bend more in one axis than the other, and is still too small, in either axis. I would be thinking more of 4" to 6" square tube, with at least 1/4" wall, 3/8" would be better.

Then,- 1/2" round/bolt? I bend that routinely with very little leverage.
Me, I wouldnt use a bolt, anyway, but a welded hook, preferably triangulated, so it wasnt a single point and a single, bendable vertical, but a couple of places where it was welded to the post, kind of like a gusset.

stainless to mild steel will, theoretically, be subject to galvanic corrosion. in real life, usually only if its in a location near salt water, but it can certainly happen. And stainless bolts/nuts will seize, unless you use anti seize on em, not every time, just the one time when you need to take it apart.

If you must use a bolt, use a 3/4" or 1" steel bolt, and weld the head to the post.

And just hanging, and letting it swing, is not a good idea unless you use an eyebolt on each part, with them interlocking- just relying on gravity is never a good idea. Gravity is tamperable, by wind, earthquakes, bad drivers, teenagers, corrosion, and lepruchauns.

Pants and Suspenders, baby.

Ries said:

Pants and Suspenders, baby.

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Forgot the belt there Ries....

You are right. I always have my belt on anyway, so I forgot it.