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?
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
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
Simpson makes some nice retrofit anchor plate attachments if needed
RE: Residential Anchor Bolts
Still the same issue. It is an unreinforced CMU wall, so where is the uplift resistance?
RE: Residential Anchor Bolts
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
RE: Residential Anchor Bolts
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
There is some calculated uplift on some of the walls (probably none in reality)
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)