Sill Plate Anchor Bolts

[ChipB]

I am designing a cmu basement wall that has a retained soil height of 11'-4" (12'-0" overall). It is restrained at the top by the first floor framing, and at the basement by a concrete slab.

Ok here is the problem, the sill plate (southern yellow pine) at the top of the wall needs to transfer 700#/ft into the floor. The floor framing is perpendicular to and bears on the plate. I can reasonably get the sill plate connected to the floor framing for the required transfer of the force. Please tell me I don't need 5/8" dia. anchor bolts spaced @ 8" o.c. to transfer the load into the plate. Is there a reference I can use besides NDS? The contractor will hunt me down and kill me if I call that out .

 

[LPPE]

What about 1/2" dia. at 48" o.c.? Thats typical residential sill plate anchors and spacing.

 

[ChipB]

Won't work.
Published allowable value for 1/2 bolt load perp to grain is 400 lbs. Load duration factor 0.9 brings it down to 360#. 4'-0" o.c. equates to 90#/ft.

 

[DaveAtkins]

On a similar project (but the wall was only 9 feet tall), I took advantage of the friction between the sill plate and the top of the foundation wall. But I still had 1" diameter anchor bolts at 2'-8" o.c. DaveAtkins

 

[CIVENG95]

Just curious, how do you plan to transfer the lateral force from sill plate to floor joist both where joists span parallel and/or perpendicular to wall/sill plate? Where joists span parallel, it seems a lot of blocking would be required to transfer the force up into the floor diaphragm. I'm from Florida so I don't see a lot of basements in my area. Thanks, Alan

 

[ChipB]

Dave,

Thought of that, except, the wall receives a decent amount of uplift from wind. The house is on the top of a mountain.
This particular wall, I haven't checked, but the wall at the back of the house, transitions from tension to compression under DL + WL just below this level.

Alan,

Stay in Florida. People will think you're crazy when you start calling out hurricane clips tying down the rafters/trusses. But on the other hand, I don't have to deal with wind borne debris any more. If you leave, go to an area w/ your college conference or you'll never get to watch your team play. Luckily, we have ACC up here so I got to watch FSU regularly. The only Florida games were those shown nationally.

Anyway, to your question, I call out Simpson connectors to the sill plate/band joist transfering a portion of the force to the band joist which then in turn transfers to the floor joist, the remaining force I transfer through the floor joist/sill plate connection with Simpson connectors as well. I block @ 2'-0" o.c. when the floor framing is parallel to the wall. I carry the blocking until the floor joist that the blocking stops on, is capable of carrying the floor load along with the tensile load the basement wall is inducing. You could possibly double up a member before then and stop the blocking sooner, but chances are, the head carpenter isn't doing the framing and it could get missed.

Now, to the problem at hand, I figured out what I'm going to do:
the floor joist are 2X10s
I'm putting in another course of block w/ a 2x8 plate. Attaching a 2x10 to the inside of the block top of which will match top of plate and attaching the joist to that. I gain 1/4" in basement floor height, but it'll take care of those bolts at 8" o.c.

 

[ronster]

Careful w/ that detail. Wood shrinks while the masonry does not. Unless your carefull the piece of floor sitting over the masonry wall will bump up as the wood joists shrink. You'll need quite few bolts with your detail to transfer the joist load into the wall from the ledger and to secure the wall above to the masonry. I've used the detail your considering when the grade comes up close to the floor line in order to keep the wood away from the soil.

Consider using 3/4" diameter anchor bolts and a double sill plate. I always use a double sill plate to keep my bolts at a reasonable size and spacing, it also makes it easier to shim and level the plate.

 

[rccon]

chipb-
I guess I'll add my two bits worth because this is a problem which has long bothered me. Most residential basements where I am (Seattle) don't get engineered, although at 11' of backfill, these days it may be required. Anyway, the reason they don't fail even though restraint at the top is inadequate or virtually nonexistent is that for typical house dimensions two-way slab action is effective, and also, in most cases the design soil load does not occur.
However, none of this helps the engineer who has to demonstrate the safety of the wall by rational means, unless he wants to do a 3d finite element analysis.

I have done such an analysis in general form and have used it when I wanted to specify that the wall can be backfilled before the deck is built, but it requires quite a bit more steel than is generally used. Still, it's better than putting in the large footing required for a cantilever wall. If you need to provide the restraining force at the top, it really does take a lot of bolts. 5/8" bolts may be good for 400 lbs. cross-grain in the wood, but what is the strength in the grout? I don't work with masonry, but it seems in an 8" or 10" wall the bolts would be too close to the edge when loaded transversely. If the load on the grout is ok, you could increase the allowable load by going to a 4x mudsill.
I think the contractor will scream louder about the extra course of blocks and the ledger and joist hangers than he will about the closely spaced anchor bolts, although the ledger is the best method of ensuring restraint of the wall. The ledger is a real pain to install, and it may come as an unpleasant surprise to the heating, plumbing and electrical contractors. I've done it this way and not had the problem with shrinkage mentioned by ronster, although it does seem a possibility. On the matter of a double sill, a single 4x would allow higher bolt loads. In my area, a min. 3x sill is often required anyway for the shear walls above.

 

[adk]

ChipB
I take it you went to FSU/FAMU COE? Me too, class of fall 98. Rough year for our boys. At least Miami lost, HA HA.

Back to engineering. Have you considered changing your floor joists form bearing to hanging on a ledger beam? This way they brace the walls in direct compression. You will have to design the floor beams in bending and compression anyway, I am assuming, unless I am missing something. You would still need to transfer this force in shear via your floor diaphragm to the side walls. So this may or may not help.

Short side story: I say a special on the WTC, regarding the reason the basement walls did not fall in. The WTC has a 4 story or so basement/ parking garage/ train station. The water table due to the nearby water is high and the soil unstable so they constructed a "bathtub" of sorts, and this cantilevered retaining wall is supported by the cross beams of the parking garage, much like I am suggesting to use your floor beams as axial braces.