Foundation Bolt Strength

[CurlyDave]

We still are curious about your concern in terms of the bolts. let's face it, if you get winds or storms hard enough to strain those bolts, I would think other things, like the roof would be gone and the nails would have pulled out of the studs. I guess the sill plate would be in tact though.

I am rebuilding my house that burned down.

I have an existing slab with footers and this particular bolt is exactly where I need a hold-down for seismic stability.

The engineer involved wants me to drill through the foundation, and footer (all 18" of it), and then embed a 5/8" threaded rod with a nut and large washer on the end in a new footer to be poured under the existing one.

Depending on whose analysis you use we only need either 5650 or 6400 lbs. of pull out strength.

Since I already have a 5/8" x 12" anchor bolt (~9" of embedment) which was wet-set 20 years ago right at the exact spot necessary, I am questioning why I should destroy this in order to produce a kludge of a tie-down with lower strength.

Changing engineers is not possible, because this is the only remaining sticking point and I need to submit plans this week in order to get moving on the construction.

He actually isn't a bad guy, but I think he has gone overboard on this one.

From the table in the article, the existing bolt would be good for 9503 lbs of seismic pull out force if it were 3" from the edge of the footer. Unfortunately, it is only 1.5" from the edge and I now have to find how much to de-rate it for this location.

Somehow, all my engineering instincts tell me it is OK, but that I am never going to be able to prove it is OK.

So, I am now starting to look for a 3/4" x 20" long masonry drill that will fit my Bosch SDS rotary hammer. 16" ones are $39.99, which isn't bad, but I haven't found a longer one yet.

P.S. The seismic loads anticipated are real. The San Andreas fault (San Francisco 1906) is about 1/2 mile from the house.

 

[JB4310]

Yeah being only an inch and a half from the edge is really gonna derate it especially for that seismic criteria, would be fine other wise IMO.

Wont they allow some type of expanding lag type anchor? They use them in bridge construction so they are rated for what ever you need.
Even if you had to put a few extras in to meet the specs.

It will be a pain to drill that far with such a small diameter bit, with no easy way to evacuate the spoil the bit may bind up as you get down in there. You can do it but... Might have to go to SDS max platform for such a long bit, I know they have 3/4x21 sds max (Milwaukee)

Rereading what you wrote almost sounds like he wants the 2 concrete structures tied together? like he's trying to kill 2 birds with one stone.

JB.

 

[2manyrocks]

Picture of this might help. I start wondering why you can't fabricate an external steel brace that ties in this point. Seems like you would lose strength to do what he is proposing. I question that the strength of all thread today installed this way is what the strength is of the existing bolt manufactured years ago would be installed in wet concrete in the first place.

 

[yooperdave]

Push back and see if the load can be resolved elsewhere or if the load can be shared with something else.

Can another segment of shear wall be used or developed for lateral resistance?

Is the engineer using drag struts anywhere to accumulate load?

It is not uncommon to play with the numbers to ponder the possibilities. Nothing wrong - just thinking ouside of the box.

Yooper Dave

 

[Pops15]

Dave,
They make drill bit extensions. I have some that are around 3' long. Can't say I've ever seen an SDS extension though. Worst case you could use an sds bit for the first 16" then use a round or hex shank bit (or maybe even an sds bit) in an extension. The problem may be the hole diameter. The part of the extension that accepts the bit my be bigger than 3/4" in diameter. Could you drill the first 16" at 1" then finish up with a 3/4" bit?
Pops

 

[Pops15]

Since you have to drill so deep you might want to rent a spline drive drill instead of using an sds set up. Whatever you use keep the bit cool.

 

[CurlyDave]

yooperdave:

In a distance of 3' , I have four 5/8" bolts on approx 12" centers. (When I built the house 20 years ago, I knew that this would be a place that required serious hold-down capability. I will push on sharing the force between several of these bolts which may reduce the problem. Another issue is what he will want to charge for doing the analysis. The labor to put in the bolt the way he wants it is ~$500. If the analysis is more than that I will do it the way he wants.

* * * * *

Pops:

If I have to drill the hole, I am going to stop every few minutes and blow the concrete dust out of the hole with one of these - Harbor Freight Tools - Quality Tools at the Lowest Prices .

While I am at it I can blow off the drill to cool it, or dunk it in a bucket of water.

 

[yooperdave]

The bolts will all share shear forces, but the 1 bolt at the end gets all the tension.

3' is indeed very slender for a shear wall.

Oh well

Yooper Dave

 

[rambler]

In following your adventure with this rebuild, I am starting to feel better about the miserable Minnesota winter, all the below zero temps, and the snow & ice I've gotten the past few months, and yet to come into spring.

Somehow, compared to what you are dealing with, this doesn't sound so bad.

Thank you.

--->Paul

 

[Pops15]

$500 seems pretty steep. My Milwaukee Thunderbolt spline drive with a quad cut bit will drill 3/4" X 6" deep in less than a minute. The trick is to keep the dust cleaned out. Drill an inch or two, pull the drill up to clear the dust, drill another inch or two, pull the drill up, etc. Clearing the dust with air should work. I'd use a watering can to pour water down the hole to keep the bit cool, lubed, at to keep the spoils from packing and seizing the bit.
Since you're going to use your sds drive drill you might want to drill a 1/2" pilot hole then finish up with a 3/4" bit.
Pops