Anchoring into SOG using expansion anchors 1

[jmaddox]

So, I am trying to make sure that I have all of my bases covered. I am verifying the anchorage of some elevated mechanical equipment to an interior 6" SOG reinforced with #3 @ 18"oc. I calced the T/C force to be 974# per base plate and the contractor used 4- 1/2" x 6" Redheads and an 8"sq base plate. I checked the bolts for combined shear and tension and get a ratio of 0.57. So the anchors work. My question is: Can the reinforced SOG take the uplift? The area of concrete required to hold down 974# with 0.6DL factored in is about 4'-9". Can I assume that the rebar will engage the reqd concrete? Is there a calculation that that determines the maximum area of SOG that can be engaged?

Thanks in advance for any help.

 

[steellion]

ACI Appendix D covers all shear and tensile modes for anchorage into concrete, in excruciating detail. Hilti has really nice (and free!) software that calculates capacity based on Appendix D, but only for Hilti and cast-in-place anchors. I think Simpson and Powers have similar programs, but I am not as familiar with their software. Not sure if RedHead does.

 

[jmaddox]

I am painfully aware of appendix D. However, I know my anchorage works between the column base plate to the slab. What I am worried about is engaging enough of the SOG to resist overturning.

 

[msquared48]

Hilti Profis does.

I have used Simpson's.

Redhead does not have a program.

If the lateral loads to the equipment are governed by seismic loads, you have to be sure that the anchors you use are qualified to resist seismic loads. Most are not.

Mike McCann
MMC Engineering

 

[jmaddox]

The ITW RedHead Trubolts Expansion Anchors are qualified to resist seismic loads per ESR-2427

 

[JustSomeSE]

If the anchors do not break out per the Appendix D calculations, then they will stay attached. You're asking yourself - am I going to fail the slab? Think about it this way - if you put these anchors into a 5'x5' piece of concrete that is 6" thick, would you pick it up off the ground? I'm pretty sure you could.

Three checks you could do:
1. Punching shear like it was column load on slab.
2. One way shear check at face of anchorage.
3. One way flexure check assuming cantilever at face of anchorage.

 

[Ron]

The values you used for the unity check were likely from the manufacturer's tables and will be ultimate or allowable depending on the manufacturer. In either case, they usually give you the values based on concrete failure (with different columns for a couple of different concrete strengths) and then values based on steel failure. You likely used the concrete failure values which gives you the answer to your question...assuming you are using allowable loads not ultimate loads.

 

[ztengguy]

Your slab is fine.

 

[briancpotter]

Punching shear check, and a two-way bending moment check - except for restraints, it's no different than if it were an elevated cast-in-place slab bearing on a column.

Brian C Potter, PE

http://simplesupports.wordpress.com

 

[jmaddox]

Ron: I used allowable loads not ultimate loads based on the MFR tables with the appropriate f'c

Briancpotter: I also checked for 1 way and 2 way shear of the SOG.

Thanks for the responses, they really help out.

 

[dhengr]

jmaddox:
On a piece of equipment like you’re dealing with, fixed to a SOG, you might consider the following: use a skid connecting the two legs on each side of the machine, that is two skids; this would allow you to distribute the gravity loads better, w.r.t. punching shear; and it would allow you to install more A.B’s. (expansion bolts) and distribute them better; and finally it would allow you to bring more of the slab into play w.r.t. the overturning moments, and the slab DL brought into play.

 

[XR250]

I would not think twice about 974lb uplift on a 6" slab w/ #3 @ 18" O.C. - it is not going anywhere.