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Residential Anchor Bolts

Residential Anchor Bolts

Residential Anchor Bolts

(OP)
Just looked at a one story house built 18 years ago. The foundation is 8" CMU with 4" exterior brick. There is no wall veneer so the stud wall aligns over the brick.
The sill plate is a 2x4 anchored to the top course(s) of the brick with 1/2"Ø anchor bolts. The bolts are too long and, as such, the nut does not tighten against the sill plate as the bolt is not fully threaded. (the nut sits about 1" high). I thought about them removing the nut and adding some spacers but the threads are so rusted that this not likely possibly given the limited access. Maybe some horse shoe shims can be installed?

Here is the question:
The bolts are providing some resistance to the house sliding off the foundation, but are not providing any uplift resistance until the house picks up 1". This is a 90 mph, exp B site so the loads are not that great anyway. Since we are not allowed to design un-reinforced masonry for direct tension stress, can we expect the average anchor bolt to provide any calculable uplift resistance?

RE: Residential Anchor Bolts

So there are no designated hold downs at the ends of any designated shear walls?

I would be worried about the more concentrated holddown areas than trying to show that a single 2X4 plate that is probably in in cross grain bending can resist any uplift.

Mike McCann, PE, SE (WA)


RE: Residential Anchor Bolts

Why not provide post installed sill plate anchors and straps attached to the inside of the 8" block at Shearwall posts?

Simpson makes some nice retrofit anchor plate attachments if needed

RE: Residential Anchor Bolts

(OP)
There is no shearwalls in this house. Very conventional 20 year old, Southern crappy construction. Probably fully sheathed, however.

Quote (EngineeringEric)

Why not provide post installed sill plate anchors and straps attached to the inside of the 8" block at Shearwall posts?
Simpson makes some nice retrofit anchor plate attachments if needed

Still the same issue. It is an unreinforced CMU wall, so where is the uplift resistance?

RE: Residential Anchor Bolts

well you can add reinforcing if needed? :)

If this is the states, i think there are prescriptive codes for residential construction IRC that has some applications with non-reinforced (plain) CMU (not brick)

Also, straps can go down to foundation for significant uplift... assuming you have enough foundation weight!

RE: Residential Anchor Bolts

(OP)
Honestly, I think I am ok with the 1" gap. Anchor bolts were not even required here until 20 years ago and I have never seen an older home have problems (on a crawlspace anyhow) even after getting hit with a fairly significant hurricane. If there is a storm strong enough to pick up the house 1", then so what? It should drop back down when it passes :>

RE: Residential Anchor Bolts

Have you checked to see if there is any net uplift? If there is no uplift, this issue goes away.

Also, unreinforced cmu can provide resistance to uplift (as in the case of an unreinforced shear wall). Although it is rather low, mortar does have an allowable tension stress that varies by application and mortar type.

RE: Residential Anchor Bolts

(OP)

Quote (Motorcity)

Have you checked to see if there is any net uplift? If there is no uplift, this issue goes away.

There is some calculated uplift on some of the walls (probably none in reality)

Quote (Motorcity)

Also, unreinforced cmu can provide resistance to uplift (as in the case of an unreinforced shear wall). Although it is rather low, mortar does have an allowable tension stress that varies by application and mortar type.
That is a flexural tension case - not a direct tension case. We all know it has tension capacity, but just have no way of using any numbers. (unless things have changed)

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