Moment in studs/bolts

[JoeBaseplate]

I have a somewhat theoretical question. We have been hired last minute to look at some canopy connections into a precast plank floor system. See attached for the general layout. The 8x8 plate and canopy is already in the field. What the contractor is suggesting is to have some welded studs/anchors to a plate attached to precast and hang the canopy off of these 4 studs (again, see the attached). I told him no way, because the studs have a huge moment arm and are going to be in bending. So he suggested that he will fill the gap show with non-shrink grout. To which my reaction was, its just a lump of concrete not doing anything structural. He somehow (along with the architect) though that this grout would avoid any bending in the studs. I am quite confident with my responses but for sake of knowledge:

1) If I was to use studs with moment, is that advisable? I would have shear, tenions and moment due to shear on the studs. What grade studs would you typically use? Is A325 an option?
2) Would you agree with my assessment about the non-shrink grout that its not doing anything structural.

Thanks,

 

[ztengguy]

What is holding up the 8x8 plate that is already there, if the studs, anchors are not there?

 

[a2mfk]

Joe,
First, this is what you should have originally posted instead of your other post. All the advice was being given was probably based on the plate being mounted to the bottom of the panel, not the end, at least that is how I understood it. You are not the first person to ask a complicated question without providing a sketch, but it is a pet peeve of many on the list... Because we are just guessing and it makes the poster seem lazy.

Second, this would also seem to be the opposite of theoretical. This has already been installed!

Third, this is a bad detail. Who came up with it in the first place, the contractor? There are WAY too many unknowns here, all mentioned on the last post. Unless the anchorage into the panel is load tested, I would not trust it at all.

I assume that is brick cladding with CMU bearing wall? You gave us some sizeable reactions on the last post. Unfortunately with that type of loading I'd want to mount it to the CMU, which looks to be covered with brick.

There are no quick and easy solutions if my assumptions are correct that I know, maybe someone else has one. My Monday morning QB comment would be this was a bad idea from the beginning, and unless a section of the brick could be removed to fully access the CMU (and possibly have to reinforce that if its hollow), a separate structure should have been provided.

Maybe it could be somewhat salvaged by:
-remove a 16" wide swath of brick at the connection all the way to the ground and several inches or more above the connection
-construct a 7x16 CIP tie column, dowel into the CMU wall, embedding the in-situ connection into the concrete column (of course you have to calc all this out)
-depending on the size of the CMU wall footing, you may need to add to that too

May be cheaper to give this all up and go with a steel column and new footing.

 

[BAretired]

1) If I was to use studs with moment, is that advisable? I would have shear, tenions and moment due to shear on the studs. What grade studs would you typically use? Is A325 an option?
2) Would you agree with my assessment about the non-shrink grout that its not doing anything structural.

How is the inner plate connected to the end of the precast? This looks like a weak link in the assembly.

How is the CMU above and below connected to the precast? Your detail indicates nothing but friction.

1) Studs with moment is not advisable. Better to weld plates between the two plates shown, but that won't help if the connection to the precast is inadequate, which it appears to be.

2) Concrete fill between the two plates will try to prevent the studs from bending, but unless there are confinement rings, the concrete could split and become useless. Welded plates would be better.

BA

 

[msquared48]

A workable solution would have been a small tube section instead of the bolts, but that's water over the dam now.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[csd72]

Not sure that I saw the last thread so my comments are based on this.

What is the anchor load on this? if small then it may be possible to replace the studs with a square tube and take the downward force into the masonry veneer.

You may be able to use the anchor bolts in a similar configuration but I would not tend to trust it.

Alternatively, have it in line with the anchor rod to create a direct tension and shear in the plate connection.

as others have said, the plate connection is the critical link in this chain.

 

[peconsultant]

It is my understanding from the original post is that the plate is in the field but nothing has been installed yet. If that is correct, scratch the idea of the 3/4" studs. Instead, weld a HSS section to the plank and cantilever the HSS out to the plate. Also, I would not put the expansion anchor into the concrete as shown in the sketch.

 

[msquared48]

I agree with PE as expansion anchors, #1 might spall the plank, and #2 do not work wedll with vibratory load conditions.

A chemical anchor would work much better.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[hokie66]

Agree with others that the bolts extending 7" is a terrible idea. A properly designed structural steel bracket is required, maybe a square hollow section with end plate. Adequate connections to the hollow core plank are not easy, either. If already in place, I would not rely on the anchorages. The same moron who proposed the cantilevered bolts probably designed the connection to the planks.

 

[JoeBaseplate]

Thanks for all the input. I met the owners and contractor yesterday and got a little more info. Apparently this sunshade was supposed to be an alternate and I guess the architect thought that it would never be given the go ahead so no thought was put in the design.

I am asking the arch to put more hangers for the sunshade to reduce the loads, and to allow connection into the bond beam under the plank. I am meeting the parties today again, I think they want to consider changing the sunshade from a grate to an open trellis.

I'll be back later to tap into more wisdom here.