J-Bolts vs concrete anchors

Posted 09 January 2015 - 09:13 AM

Let me first preface with the fact that I realize I don't have the "normal" pier.  That being said for my design J-Bolts would never work.  I actually started with 4 J-Bolts that were on the top of the round concrete pier.  This was when I was only going to have a ROR design and a short pier.  When I flipped my design to a Dome the height of the pier had to more than double and the overall pier/base design changed considerably.  With only 4 to perhaps a max of 6 bolts, a J-Bolt design works well and if you follow the guides in mounting them as other posts on this thread have mentioned you should have no issue.  When my design changed my bolt count went from 4 to 20.  The thought of trying to exactly position 20 bolts precisely embedded in concrete is, quite frankly, ludicrous. 

Here is a basic CAD view of my pier:

It's a little tough to see but the steel pier is bolted to the concrete both at the base (12 bolts going around the base) and there are 8 which bolt the next level up to the top of the round pier.  The 12 around the base are basically 6 primary bolts with an additional 6 that are spares against a failure.  Since the holes were cut in the steel with a CNC Plasma cutter, cutting 12 was just as easy as cutting 6.  Drilling the concrete was just as easy (later shown below).  The 8 bolts on the top (the original 4 J-Bolts were cut off at the top as they could not be used) are used to "load" the steel 2x4 uprights.  That secondary steel plate is actually about 1" above the level of the concrete.  This is by design.  Once in place and the bolts were anchored and cured they were torqued down.  The gussets transfer the downward pull on this plate to the uprights loading them.

This is the pier in place before the holes were drilled.  We placed the pier (over 1000lbs in weight) and then drilled the concrete with the pier in place.  Given the weight, once the pier was down it was not going to move.  You can see the un-drilled placement here:

Drilling the holes was a snap with a Hilti power drill.  My son has a metal fabrication business and owns this drill for doing installations of steel assemblies he manufactures.  You can rent these.  If you opt to use anchors instead of J-Bolts and you have more than 4 holes to drill you might want to consider it.  I was curious so I timed it.  We were able to drill a 5/8" x 6" deep hole in the concrete in 12 seconds.  This thing laughs at concrete.

We used both anchor bolts and then to be redundant we put industrial concrete epoxy in the holes in addition to pounding in the anchors.  In 20/20 hindsight we should have just used epoxy with straight bolts not even bothered with the hammer/anchor bolts.  The epoxies you can purchase these days are much stronger than the concrete around them.  The epoxy made it difficult to hammer the bolts once they were placed inside the holes.  We got it to work but like I said, using the anchors was probably not required.  Here is the finished pier:

So, I would say that if you have 4 to maybe a max of 6 bolts you are wanting to use to anchor your pier, J-Bolts are the way to go.  I would follow the good guidance on pouring your concrete and placing your bolts as others have posted.  If you have more than 6 bolts I would recommend using anchors.  I would drill after placement of your pier, not before and I would recommend only using industrial epoxy instead of anchors but you could use either.  If you use anchors I would recommend some redundancy in your bolt placement as has been mentioned, anchors are more prone to a failure than a J-Bolt.  If you have some redundancy, this should not be an issue.