Canopy anchorage 3

[Heldbaum]

Guys,

I am going back and forth with EOR regarding calculations for canopy anchorage. They want to anchor new canopy structure to the edge of reinforced concrete slab. RC slab is reinforced top and bottom with #5 bars @ 12". I used four (4) SS Threaded Rods on epoxy or grout with 12" embed. plus I want them to make holes(pockets) for Hex Nut with washer.(See attached picture)But he doesn't want to agree on that, I am not sure how to include this in my calculations and the fact that we have rebars there...do you have any useful references/examples or any ideas? Thanks!

 

[JGard1985]

Hi

Why do you want holes/pockets for nut with washer. Seems like if you epoxied in threaded rod should be sufficient. How do you get the nut and washer into place. Seems like you'd be drilling a much larger hole for no real benefit



Jeff
Pipe Stress Analysis Engineer

http://www.xceed-eng.com

 

[Heldbaum]

Hi,

JGard1985 just to increase bearing area but yeah epoxied threaded rods will be sufficient. Just this guy is very anal
Best!

 

[NorthCivil]

I don't think this EOR is that anal. From his perspective, I think he is just a bit concerned about your detail, which is going to completely shred the edge of the slab!

I think you are overthinking the slab side of this connection. what are your loads? check your math again. you likely could get away with 1 or 2 lengths of 4" long, 5/8" threaded rod epoxied into the concrete. no nut required, what a mess it would be to install that!

Hilti profis software is a great design aid tool for this. its free too.

your connection details for the steel on the canopy connection side are a bit weird too. Right now you are driving those 4 rods that are standoffs into bending.

sorry to be so critical, just trying to help.

I would design this as a 1/4" steel flat plate that sits on the slab edge. two 5/8" threaded rods or 15M rebar welded onto the plate, that are drilled and epoxied into the edge of the slab. then weld on a couple knife plates, or something else equally positive, to restrain the cable or canopy hinge.

 

[Lnewqban]

Just another suggestion:
Consider that the flat surfaces of the nuts-washers will not sit against a flat surface, unless you cut it with an abrasive disc.
For that reason, they will not be effective in creating and keeping any tension on the rods.

Could you fabricate a steel angle with a hole on its horizontal web and drill perpendicular to the slab?
If so, you could weld any desired shape of anchor-plate perpendicularly on the vertical web.

"Where the spirit does not work with the hand, there is no art." - Leonardo da Vinci

 

[txeng91]

Agree with EOR, no need to break into the slab if you don't need to. The failure mode here is concrete breakout because you are anchoring into such a thin section, and you should be able to achieve all the force transfer into the concrete you need with the epoxy. Regarding the rebars, I would not count on it to supply any additional capacity since you are post installing and you would have to drill very deep in order for the breakout cone to have any significant overlap with the rebar. Like NorthCivil said I would run this in Hilti PROFIS like you are anchoring into cracked concrete with no tension reinforcement. You also might want to consider going to 2 anchors side by side in the middle of the slab so you are not drilling so close to the slab edge and 4 anchors isn't going to give you much more capacity. Just a warning on Hilti, it lets you input your plate thickness, but does not actually check the plate for the bending forces that will be induced in order to transfer the forces to the bolts so you will need to make sure your plate thickness is adequate for the load.

 

[Heldbaum]

Thanks guys !I really appreciate it !

 

[HouseBoy]

How are you resolving the vertical load at the edge of the concrete?

Seems like the anchors must be designed of combined shear and tension, slab checked for bending as plain concrete (considering lack of development length if anchors are relatively shallow) and if the bolts are "hanging out there" they will be in bending too.
Shear from gravity load (I assume) and tension and bending due to eccentricity.

Perhaps I am missing something -
Responders here seem to be suggesting a "less intrusive" connection.
I'm not sure if EOR is thinking you are too conservative or too un-conservative.
"Cantilevered" bolts were mentioned above.
Someone mentioned a steel angle bearing on top of the slab at the edge. Seems like maybe that is needed but I don't know all of the loads.

Just what is the objection from EOR?

 

[bookowski]

You're drilling 12" deep holes 2" away from an edge and 3" on center. I would refer to that as demo. Perhaps propose using dynamite to blast the edge of the slab and then recast it with an embed for the canopy.

You said that epoxy anchors are sufficient in your 2nd post. Do you have calcs for that? If so what is the objection? Based on your sketch, which I assume are your hand calcs and not what you're submitting, you have unfactored moment of 16.8 kip-in. Assuming most of that is live (snow/wind) and only minor dead then lets say ultimate is roughly 25,200 in-lb. I think you'll have a hard time getting an anchor arrangement that meets the edge distance and spacing requirements in an 8" slab to take that load. And what about the shear?

Since you're asking here how to account for the nuts on your d.i.y. anchor system I'm guessing that you didn't submit any justification to the EoR? If you're a pe submitting to another pe I'm not surprised that he's not very impressed by your argument of 'the nuts are extra' and no calcs to back it up.

You also haven't addressed the slab itself. The EoR is reviewing loads imposed? I'm assuming this is a slab that was not originally intended to support a canopy or you wouldn't be doing this. If that's the case then are you sure that the slab can even take the additional load (moment, shear) - regardless of anchorage?

Based on your loads this is a decent cantilever, I wouldn't mess around with inventing anchor systems with no justification for something overhead with no redundancy like this.

Why not use a tie rod or similar so that you don't have cantilever moments to deal with?

 

[KootK]

I've made a proposal below. Related comments:

- I'd only go this route if you're unable to negotiate tie rods and a conventional slab edge connection won't work.

- I believe this to be what Lnewqban and HouseBoy alluded to previously. Obviously, you need to have the spatial clearances required to make it happen.

- It's a very convincing connection with regard to shear transfer. Just bearing.

- It's a reasonably convincing connection with regard to moment transfer. The compression part of the couple is just bearing against the slab edge. The tension part of the couple goes from the bracket, into the topside bolt, then into the concrete and possibly the slab top steel.

- I'm assuming that, while uplift loads may be present, downwards load will dominate.

- Arrangements would need to be made in the cladding element sandwiched between the slab and the canopy to facilitate the install.

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.

 

[Heldbaum]

KootK Thanks a lot ! Thank you everyone for your advices.

 

[MotorCity]

In your sketch, you indicate a factor of safety of 2. Where does that come into play? For anchor design, whether you are using tables from a catalog or software from an anchor manufacturer, they already have the appropriate safety factors built in (usually they are much larger, like 4 or 5). As for the concrete design checks, safety factors are not used in strength design. You may be over penalizing the structure by using higher loads.