Hilti vs embedded anchors

[70runner]

Plan for steel barn on 24'x36' slab/piers calls for 5/8in hilti bolts (4in deep) at 10 anchor points. I called the engineer and asked why they specify hilti's vice embedded anchor bolts. He said mostly because of precision needed for placement. My sense is embedded anchors would be stronger. Can anyone relate the strengths?

If the strength difference is significant I would probably go with the embedded anchors since the barn is in a high wind area and I'm doing the excavation and forms myself.

 

[Ron]

70runner...yes, embedded bolts provide more resistance than Hilti or other drilled anchors, whether epoxy, acrylic, or wedge type.

Having said that, if the engineer has appropriately designed the anchors, he can do that successfully, even in high wind areas. Make sure he has considered the spacing of the bolts (the closer they are, the lower their pullout resistance), the embedment depth relative to the concrete thickness, the edge distances, and the probable failure mode of the anchors. All play into the design. Further, most building codes require that a safety factor of at least 4 be used for anchors and that shear-tension interaction be checked. If you have a lateral load (probable) then this parameter must be checked.

 

[70runner]

Ron, thx for the response. Plans specify min 4in embedment for KB-II Carbon Steel Hiltis. There are 10 concrete piers approx 12' apart. Anchor bolts for the connector columns are placed at center of each 24" diam x 42" depth pier. Corner columns (4) have an additional anchor bolt for a hold down clip. Support columns (6) have an additional 2 anchor bolts for baseplates. (I hope this is making sense).

I plan to embed the 10 connector column anchors in wet concrete, using 10" long 5/8" anchors. Rather than try to get an exact placement on the other 16 anchors for the pour, go with the hilti's for the clips/support column plates. This should improve overall strength.

For the piers I plan to use sonotubes, since I'm digging with a backhoe. And a 2" deep tamped 3/4- gravel underlayment for the slab. Ground is hard clay (SOCAL).

 

[Ron]

Whatever you embed in the concrete should be threaded with a nut and washer on the embedded end. This will increase the pullout strength tremendously.

 

[Screwman]

I don't think you will have any trouble with the strength of the Hilti anchors in that application. You will be working well within the design envelope for that size and depth of engagement.
My 2 cents would be to use what was specified. You will possibly cause yourself more erection problems with misaligned anchors than you would gain in strength.

Dick

 

[UcfSE]

If properly design the Hilti anchors should be fine. It's easier to place those once the concrete is cast rather than try to do a bunch of measuring to wet set an anchor. In some areas the building code requires special inspections for post-installed anchors or you have to use twice the factor of safety. It might be a good question to see if that is required. Expansion bolts have a tendency to be installed questionably, particularly where tension is concerned. The hole may be drilled too big or get "wallered out" by an overzealous worker. This is just a bit of field experience talking.

 

[70runner]

UcfSE "The hole may be drilled too big or get "wallered out" by an overzealous worker. This is just a bit of field experience talking." Precisely my concern. The barn company is a reputable outfit, and have put up several barns in the area...but I'm concerned about a sloppy (weakened) anchor job.

Dick, you make a good point, it comes down to a tradeoff between placement precision and pullout strength. If I'm setting the forms, I feel like I can get the necessary precision on at least the 10 primary anchors to wet set them.

70-80mph winds are not uncommon during extreme SOCAL Santa Ana conditions, and I live on an unsheltered bluff in an area which generally experiences the highest wind speeds. Color me somewhat paranoid.

 

[dwedel]

Let see, you live in Southern California, on a unsheltered bluff, 70-80 mph winds, wildfires, mudslides, and earthquakes. O yeah, don't for get the human element as well; gangs, crime, etc. No, I'm not calling you “too” paranoid. ;-) I’ll stick to Eastern Montana.

Here is the Hilti website

http://www.hilti.com/holcom/modules/prcat/prca_main.jsp

We have used the epoxy to hold in the anchor-bolts for some smaller natural gas field compressors, which withstands a fair amount of vibration. Not sure if the size and all match up to what you were thinking. Our anchor system is somewhat more elaborate than what you would want on a barn. However, I think you could epoxy in some nice ¾” studs with the epoxy system. Our experience is the epoxy with the correct embedment length will pull out the concrete before the epoxy fails. I would think that a well stocked rental store would have a good hammer drill you could rent.

However if you are placing wood sill plates over the anchor bolts, I’m not sure why you would need the precision. Maybe I am misunderstanding your application?


dwedel
Hotrod Big Engines!

 

[70runner]

dwedel, usually the gangs won't bother with barns and, fortunately, gangs and equestrian folks don't mix real well

Accuracy of anchors is critical as its a prefab steel barn. The barn outfit does the install, drills for the anchors, etc. I watched them put up similar barn down the street from me and its a good job but they seemed in an awful hurry.

 

[dwedel]

Would they mind if you drill and epoxy the anchors? It sounded like you were doing the concrete work. This might be the best of both worlds. I would agree, that you want to have good quality control with the anchors.

Anyway, my 2 cents. Good Luck,

dwedel
Hotrod Big Engines!