Highly-loaded anchor bolts in shear

[JSA2]

I have some very highly loaded anchor bolts ("through bolts") in shear. The service load shear force is 32kips to the worst case bolt of an 8-bolt group. The bolts are "through bolts" through an 8" slab with a thick steel plate at both the top and bottom of the slab. The concrete crushing of the bolts in shear will be restrained by the top plate. (The bolts are shear-loaded from the top of the slab.)

I imagine that ACI 318 Appendix D will be too restrictive and will not provide guidance on this condition. Does anyone know of any resources which would provide contemporary limit states for highly-loaded anchor bolts in shear when the concrete crushing limit state is restrained by the top steel plate?

 

[gte447f]

You have stated that you are waiting for the design engineer to provide correct calculations. If they can provide calcs that satisfy the various failure modes you are concerned about, so be it, end of story. If not, then why not abandon this detail in favor of an embed plate. The design citeria for an embed are perfiectly well documented and spelled out.

The choice to use post-installed anchors like this in new construction seems an odd one to me in the first place.

 

[JSA2]

gte,

The current design envisions threaded high-strength rod cast into the slab. The anchors themsleves would be cast-in-place through rods.

Regarding the likely resolution of this peer review, I agree. I expect that she will go back and use ACI 318 Appendix D to get the right bolt size and we will reinforce the concrete in the vicinity of the connection.

The advantage of the connection as envisioned is that you can't have pullout of the anchors. The bottom plate prevents that failure mode. A more conventional embed plate would have this pullout as a risk.

 

[a2mfk]

You could use that same detail if you want, replace the bolts with a couple of HSS members (shear lugs) welded to both plates. You can as a peer reviewer simply suggest an alternative detail, some details are just not very good (have done it on my own dwgs).... Working way to hard on a bad detail IMO.

 

[gte447f]

I see... I didn't realize the rods were cast in place. I thought they were post-installed through drilled holes.

In your case, the construction sequence is analogous to setting of anchor rods for a typical column baseplate. The use of templates can't be relied upon for accurate results. Templates are always used, and anchor rods are routinely misplaced. Therefore, in my opinion you should avoid loading the anchor rods with high shear loads, as suggested by AISC. Use a shear lug instead.

 

[JSA2]

a2mfk,

The tube shear lugs are a good idea, should the bolt sizing become unworkable.

 

[hokie66]

I disagree with gte447f that this detail is similar to column anchor bolts in the difficulty of location. I have used a similar detail frequently, and the workers in the field love it because they can precisely locate the fitment on the formwork and nail the bottom plate to the form. The key is to get the assembly in place before the reinforcement.

 

[gte447f]

hokie66, note that in this case, the intent is to cast the anchor rods in the concrete, then attach the bottom and top plate/base plate during steel erection. Now, if the bottom plate was welded to the anchor rods as part of an embed assembly, I would probably agree with you, but I would probably still specify oversized baseplate holes just in case.

 

[SAIL3]

Flat pl shear lugs might work out better than a tube section in this application as it would require much less space. Anyway, if tubes are used..check the local buckling of tube walls for the bearing stress.

 

[hokie66]

gte447f,
I went back and looked at his sketch. Hard to figure why or how you would cast those bolts in as shown. Double nutted to formwork, maybe. Won't make him popular with the formworkers.

 

[gte447f]

hokie66, I agree.