Residential basement foundation wall anchorage.

[K2skis]

Does anyone have any comments or suggestions for designing residential foundation anchorage? The 2006IRC code came out with tables R404.1 (1-3) to address this situation. In PA, and MD the politicians in thier infinite wisdom removed these tables from their addopted codes.

I don't argue the fact the some of the bolt spacings seem a bit overkill (7" On-center). I have run all the calculations myself and the numbers yield spacing way less than 6'on-center for inground foundations. Instead of fixing the equation they just threw the answer out the door.

It is also my understanding that these tables are removed all together in the 2009IRC. How does this happen and how can they justify throwing out the engineering behind the design.

I have been out on numerous foundation that were failing or showing signs of failure. Just curious to hear anyone elses opinion on these tables and the enforcement of the code.

 

[concretemasonry]

The decision to decrease the bolts spacing was apparently predicated on panelozed construction that does not act like a conventional continuous wall like concrete or concrete block which act a s single unit if built properly.

The panelized walls are frequently required to be used without a concrete footing and there have been some problems with the walls acting like a continuous wall due to possible vertical movement.

The codes took the easy way out and wrote for the worst possibility even thought the code is generally prescriptive.

As I understand, the sections were removed from some state and local codes since the entire question is being reviewed for the new code versions whenever they get past the politicing and hopefully get to either engineering or proven performance.

Dick

 

[jwilson33]

In PA, the anchor bolt section was removed after the builder's association mobilized against the politicians. So now we are back to 6' o.c. which is about as silly as 7" on center.

It didn't help that some inspectors wouldn't bother to understand the code and just asked for 7" spacing regardless, even for slab on grade construction. I had a few of those panic calls.

I've seen numerous foundations as well - the only "well built" ones I see moving are those with a lot of unbalanced fill or major water issues. In my opinion, there must be a substantial benefit from the weight of the house bearing on the wall. Plus there is a lot of benefit from corners and wall jogs.

And with respect to PA, they are in the process of establishing a committee of engineers, builders and I'm not sure who else to review new codes and make recommendations about what is or isn't in the best interest of the state. This concept may get its first test with the 2009 sprinkler requirements.

Hopefully, the next version of the code will be written with some common sense that the everyday mason, inspector and coop student can easily read and follow. I would like to see a simple table that says something like AB's at 48" for backfill up to 5', 32" o.c. for backfill to 7'. Something like that, but not specifically. When asked, I'll suggest to builders/architects that they should go 32" for relatively tall walls with substantial backfill.

 

[PSlem]

I asked several counties in GA and was told by all to ignore new spacing. If you do the calcs you find the new spacing takes all the basement wall thrust by the anchor bolts. Clearly the house weight and friction is doing a lot.

 

[K2skis]

I agree with concretemasonry that the issue came more to light more with premanufactured foundation systems like superior walls. But I believe this is only due to the fact that it is an engineered system that required proven code compliance.

The other issue is they still need to complete the load path and get the forces into the floor diaphram. I don't know if I buy into the whole friction theory I'm sure it helps to some degree but to what extent I'm not sure. Think of the condition where the floor framing is parallel to the wall. How much friction force can a rim board add on the outside edge of the sill plate. But heck lets due some testing I've been wrong before and if so it is certainly an easy calculation to perform.

What kind of coefficient of friction would anyone recommend for wood to wood contact?

Jwilson33 said PA was putting together a committe to address this issue. I was up at the PA Building Official Conference last month and they didn't say anything about it. I even brought up the subject at a round table discussion. They need to get some engineers involved the Home builders association seems to be against making homes structurally sound at times. That might not be a fair comment but they are certainly against anything that makes a house cost more to build. They have a very strong lobby.

 

[jwilson33]

K2skis-

The load path issue was resolved, at least partially. Simpson had worked up some engineering and had some recommended details. I have not looked at it since PA deleted these requirements. Solid blocking and other requirements would take care of the parallel condition.

The council I referred to is currently called either the Technical Review and Advisory Council or the State UCC Advisory Council. I don't have any other info on it at the moment.

As for the builders, I didn't hear too many serious complaints about the costs as long as enforcement was consistent and all builders had to carry the same cost. But this went down at the same time as a bunch of other code changes, so the impact was tempered a bit.

 

[PSlem]

My other complaint is they limited width to depth for daylight basements. Since the road is usually at the ridge the front (long) wall of the house is full height basement. For our sois, SM, this means no 8' bsmt if house is wider than it is deep.

 

[jwilson33]

I can't argue with the concept of this requirement. It sounds excessive to have the house that deep. FWIW, I just had a client add three 12" block shear walls inside his foundation wall. They were required to brace the 9' Superior Wall panels that were leaning in about 9" at the top on the fill side.

About 3" of that movement was the house warping in on itself. Even the interior lally columns and the daylight wall were leaning the same 3" at the middle. The other 6" was due to the walls moving under the house because the anchor bolts and sill were not connected to the rim joist. It doesn't help that it was 2-sided manufactured house so that the plywood diaphragm was really only two at 14ft deep, not one big diaphragm at 28ft.

 

[K2skis]

jwilson33,
You brought up an interesting thought. I think your 6" sliding occured due to them not nailing the rim joist to the sill plate with toe nails 6"on-center per code correct?

Off subject: I investigated a 6 unit townhouse building that had the 2nd and 3rd unit roofs slide right off the building due to them not nailing in the side trusses to the party walls below. Would not have believed it if I didn't see it myself! The end unit was undamaged!

My wondering mind says on big superior wall jobs. What keeps the superior wall itself from moving or sliding on top the gravel foundation? The floor slab in the typical installation has a perimeter board nailed to the wall so the slab will not contribute much if anything to prevent the wall from sliding.

I have never know this to be an issue but certainly may deserve consideration on certain designs.

 

[jwilson33]

K2,

This was a manufactured house which should have had straps wrapped around the sill plate, or something like it. But there were none.

In their infinite wisdom, the house manufacturer used 2x2 ledgers to support the joists. Once the foundation moved in beyond that point, there was no support for the front wall of the house vertically either.

 

[bigmig]

This post may have been talked to death, but I feel like I need to add my 2 cents. It sounds like most of you are from back east. In the west, I have never heard of anyone using prescriptive foundation wall bracing. I had too look up that table and learned something new. We solve the problem in 3 steps. Solve the very simple free body. Look up the values for bolts in concrete in the NDS and size/space accordingly. And then finally, what most of you are missing, is check your floor diaphragm per IBC Table 2306.3.1. I would like to see the day an AFFORDABLE horizontal wood diaphragm carries 810 plf (9' tall wall, 9' retainage, Table R404.1(1) successfully. Even if you had some monster bolt connection, your floor will buckle from all the load. Or, as some of you are seeing, the diaphragm will push everything else out of the way as it tries to relieve itself.

The bottom line is design walls with bigger footings, which in turn lessens the load on the diaphgram and creates a much better system. If you can't get a footing to work, add a horizontal stiffback beam that runs between buttress or counterfort supports.

I'm aware that the superior walls depend on support from the basement slab, but consider this, your slab won't be supporting much when it settles or heaves and CRACKS, which the last time I checked, is pretty common. Suddenly you have a 9' wall depending on cohesion and friction for sliding support.