ACI-318 concrete anchorage problem with Simpson Anchor Designer Software program

[Schambach]

I'm really struggling with this topic. I'm utilizing the Simpson Strong Tie Anchor Designer Software and I'm having a real hard time getting any anchors to work. Maybe what I'm trying to do is as impossible as the program is making it seem. I'd appreciate some help with this.

What I have:

I have a steel-reinforced concrete pit wall that is 10' in the ground and braced at the top. The wall is 10" thick and reinforced appropriately for the soil and hydraulic loads that it will be subjected to. In the plane of the wall I have a W12x22 column that needs to be anchored at finish floor height. I have a shear load (non-factored) of 6.6k and 22 ft-kips of moment. My anchor spacing that I'm trying to get to work in my base plate is 16" apart.

What I've tried:

I've tried a four-anchor solution (two at each end) and that doesn't work in the program because my edge distances are too small. I've tried a two-anchor solution so that I could center a large anchor in the center of the wall and have 5" edge distances. This doesn't work according to the program............and I think OSHA might have a problem with me not having a 4-bolt anchor situation for erection purposes. I've tried plugging this into the program using the previously mentioned moment AND shear forces and it doesn't work. I then tried breaking that moment into an uplift force-only (figuring I can try and handle my shear forces separately) and that gets me a lot closer but still nowhere near working. I'm not sure what else to do.

Questions that I have:

1. I am factoring the loads to put into the program which I believe is correct.....right?
2. Regardless of embedment depth, the program doesn't allow anything to work. I recognize that short embedment depths could cause problems but I have a hard time believing that 48" of embedment is going to cause problems when I'm loading a column in the plane of the wall. What am I missing?
3. Should I even be using this program? Can I look at this wall as though it's a couple 10" x 10" columns side by side, use stirrups where my anchors are going and embed anchors with enough depth that I get the appropriate development length that I'm not popping concrete out?
4. How would you engineers on this site approach this problem? I'd really rather not have to thicken my wall at this point if I don't have to. Do I just need to face the music and thicken it? Can I make an embed bracket with a shear lug on it so that my shear forces are transferred into the concrete by the lug and then my steel studs that are tied to the plate handle my uplift forces and shear forces on this column? My gut tells me that I should be able to place reinforcement in the wall such that I shouldn't have to worry about edge distance if I keep my anchors within my "cage" reinforcement.
5. If I was able to get a two-anchor solution to work, is there any way that I can erect this safely (it's only an 18' tall column) in terms of what OSHA would require? Shoot.......my base plate will be thick enough already that by the time I anchor this thing to the concrete, it's NOT going to go over sideways any easier than any other 4-bolt anchored column.

Thanks for your thoughts!

 

[jayrod12]

Can you provide a sketch of the configuration? I'm just having a hard time understanding how it's all fastened.

 

[Schambach]

Not sure if I did the correctly before. Hopefully this ends up in the same thread.

 

[jayrod12]

Yes that worked. Sometimes I find that their software is a little over-conservative in this regard. You may be better off having rebar threaded to accept the nut (assuming this would provide enough tensile resistance) and then using Hilti's rebar calculator to provide an adequate embedment length such that you are spliced with the wall vertical reinforcing.

I haven't used simpson's software, does it give you the option to select that there's supplementary reinforcing to help with tensile reinforcement.

 

[jdgengineer]

Unfortunately, Appendix D frowns heavily on these conditions.

Yes, you want to put in Factored, Strength level loads (including overstrength factor as necessary) into Simpson software. They have a load combination generator you can use as well.

Do you know the wall reinforcing? If you know what the wall reinforcing is you may be able to lap your epoxy anchors in deep enough in the wall to utilize the existing reinforcing to restrain the concrete breakout mechanism. I'm assuming this is what is governing so this may solve your problem. This assumes you know the reinforcing and it is relatively well reinforced.

I believe OSHA allows 2 bolt patterns if you can classify your supporting member as a "post" and not a "column". There are limitations on loading conditions and weight for this to apply.

 

[jdgengineer]

Sorry, if this is a new wall, I would add additional reinforcing (hairpins if they will fit) to restrain the concrete breakout mechanism. These would be developed into the main wall reinforcing. Simpson Strong-Tie software has a checkbox to "ignore concrete breakout". If you properly develop the anchor into the wall to restrain the breakout you can check this box.

 

[PostFrameSE]

I can calculate embedment lengths to keep the base plate down if that's acceptable jayrod12. I could provide stirrups but in a 10" wall I'm not sure how hairpins would work. Would stirrups and vertical reinforcing kind of accomplish the same thing? I know what the reinforcing is because I'm designing the wall. As you mention jdgengineer I can embed rebar far enough to restrain concrete breakout. I just appreciate the advice because I'm just a little afraid that there's something I'm overlooking here as a result of the program not giving me anything close to working. Thanks for the thoughts on OSHA as well.

Anything else that I'd need to concern myself with?

 

[jdgengineer]

Page 443 of ACI 318-11 has a good picture of the hair pin or straight bar reinforcement to constrain breakout. I don't think stirrups would help here for the anchorage -- it's essentially a development length issue.(although you would likely want some under the column to meet ACI 318-11 7.10.5.7). I'm not entirely sure this applies to walls, but we typically put them in.

 

[jayrod12]

is pilastering the wall at the column out of the question? It may be a prime candidate for something like that.

 

[PostFrameSE]

What section are you referring to jdgengineer that has that picture? I skipped over the 318-11 and just have the 318-14. I see quite a few images in Chapter 25.7 of the 318-14. I agree that stirrups won't help with anchorage but for the high shear forces, wouldn't it help to prevent the anchor from "knifing" through the concrete and potentially causing some breakout? What is the 318-14 equivalent of the section cited?

Jayrod........pilastering the column is pretty much out of the question if there is any way that I can get this to work WITHOUT doing that.

 

[jdgengineer]

in ACI 318-14 it's page 241. Before you finalize the design you should become familiar with Chapter 17 (old Appendix D)

 

[PostFrameSE]

Got it. Thanks for the advice!!! Thank you all!

 

[MotorCity]

Um, are Schambach and PostFrameSE the same person? You both respond as if you are the OP.

 

[PostFrameSE]

Yep. Not sure how that happened.

 

[KootK]

You may be better off having rebar threaded to accept the nut (assuming this would provide enough tensile resistance) and then using Hilti's rebar calculator to provide an adequate embedment length such that you are spliced with the wall vertical reinforcing.

This would definitely be my solution. I'd probably splice some full length vertical rebar directly to the deformed bar anchor bolts and not bother with the Hilti stuff.

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.

 

[jayrod12]

not bother with the Hilti stuff

Me either now that I know the wall is new. Because he was using the Simpson software I assumed it was an existing wall he was drilling into.