Rebar Loop Pullout Strength

[AM424]

Hi, I am new to this forum and have a question regarding rebar loops cast into a concrete ceiling. I am a mechanical engineer and have not done anything with concrete before this, so I am looking for some guidance/advice.

Here is some background of the situation. We have an existing concrete ceiling with several #6 rebar loops cast in place that we are looking to hang some piping from(2000lbs). I have the geometry of these loops and have determined that they can carry the load just fine from a mechanical standpoint, but my concern is the load on the ceiling. This is an area that I have not dealt with before. Are there any resources that I could be pointed to to determine what kind of forces it would take to pull these loops out, or is the main concern going to be the load on the slab itself? I know it will depend on the composition of the slab, so I have included the details that I have on hand from the drawings used during construction.

Slab Dimensions: 36' x 40' ceiling 12"thk. there are no intermediate beams or columns in the room, just floor walls and ceiling.
Reinforcement: #6 rebar 6" center to center both ways, top and bottom

If anyone could even just point me in the right direction I would greatly appreciate it!

Thanks!

 

[KootK]

The PCI manual has provisions for embedded prestressing strand[] loops. I don't know of anything for rebar though. The stiffness of the rebar makes that a bit different of a problem. I'd not want to do this until I saw some test results or a design method published by a reputable source.

 

[JedClampett]

AM424, please send a sketch or picture. You might be explaining this perfectly, but we structural types hear #6 loop and think something completely different.
It's hard to bend a #6 bar in a loop to fit in a 12 inch slab.

 

[HTURKAK]

Could not imagine the slab with Dimensions: 36' x 40' ceiling 12"thk. and without intermediate beams and with Reinforcement: #6 rebar 6" center to center both ways, top and bottom and #6 rebar loops .....
I assume 2000 lb is the total wt of the subject piping and the load to each loop will be in the range of 500 lb ..

I will suggest you to load test the loops and see the situation.

Pls post at least some design drawings excerpts , some photos to get better responds..

 

[AM424]

First off, thank you all for the responses. I really appreciate it!

KootK, I will check out the PCI manual and see if I can glean any info from it regarding this situation.

Jed, I have attached a few screen clips for a visual description. A better way to describe the loops might be stirrups that protrude and have a "u" loop as the protrusion.

STIRRUP DETAIL

HTURKAK, I have added a few screen grabs of the original prints that show the some of the dimensions of the slab. My initial though was to load test them, but we want some form of calc to back up the load test. You are correct in assuming the weight will be across multiple loops, 4 or 6.

SIDE VIEW

TOP VIEW

 

[bones206]

Was the original purpose of these to be hanger attachment points? If so, I imagine the design load would be stated on the original drawings somewhere if you have them.

 

[Lomarandil]

The difference between a stiff rebar embed loop and a flexible prestressing strand does have some worrisome characteristics, but they're used quite commonly in lifting (precast concrete, deadmen for construction). I wouldn't be concerned for a 2000 lbf load on a #6 loop.

The global analysis of the roof for the additional load will require more information (environmental cases, what's above and around). Easiest if you can send that to your local structural engineer. Although depending on the applicable building code, you may get away under the "less than X% change" provision.

The issue I think is most likely to control this installation is the anchorage of the embed loop into the roof. One could pretty quickly calculate the capacity of a pair of L-bolts embedded into 10" of concrete (or just one for simplicity). You'll have a little more capacity because of the slab reinforcing, but that's harder to quantify.

----
just call me Lo.

 

[HTURKAK]

The total piping load 2000 lb and for each ( # 6 anchor ) 500 lbs .. If you divide the 2000 lb to the area , 1.3 lb per sq-ft..it is almost nothing..
But to make sure, obtain the calculation report and see the roof slab design loading..

Good luck..

 

[Lomarandil]

I wouldn't simply divide the 2000 lbf or 500 lbf load by the entire roof plan area for the global analysis. Some portion of it, sure, but that would depend on the anchor layout.

----
just call me Lo.