Residential foundation wall - lateral support - anchor spacing. 1

[hines86]

Has anyone ever thought to use the stability bracing equations that you would find in appendix 6 of the AISC for anchor bolt spacing on residential foundation walls. I am sure the equations would need a bit of tweaking for material properties, but could this be the answer to why anchor bolts are prescriptively allowed to be spaced as far as 6' O.C.?

If you have any literature on the topic that would help. I would greatly appreciate it.

Thank you

 

[KootK]

I'm not sure that I follow Hines. The AISC provisions are for bracing a primary member prone to buckling. That's not really an issue with basement walls. If your load path for bracing the top of the wall passes through the anchor bolts, I would expect that to be governed by lateral earth pressures and the anchor bolt spacing to be pretty tight.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[hines86]

As a design assumption for foundation walls you analysis it as a simply supported beam, typically. Although in an example published by ACI concrete basement wall are in reality a cantilevered beam. You have a ridgid connection at the base and a flexiable connection at the top of the wall. The connection at the top of the wall is viewed as a redundant support/ brace. For lateral stability purposes/ buckling at the connection between wall and floor.

 

[KootK]

I get it now - thanks for the extra info. While I've never heard of anyone checking this, I agree that checks similar to the AISC provisions would be appropriate were one to attempt it. Some ideas:

1) I would treat the wall as a rigid element pinned at the bottom and laterally restrained by a spring at the top. In residential construction, basement wall footings typically aren't substantial enough to provide significant rotational restraint.

2) With regard to initial misalignment, be sure to consider reasonable concrete tolerance values rather than steel tolerance values.

3) Lateral earth pressure loads can be expected to dominate the design of the connection which is probably why this is an uncommon check.

4) Assessing the stiffness of the connection and diaphragm would be tricky.


I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

I bumped into the attached document during the course of my normal work this morning. I thought that it might be of interest to you. It doesn't deal with any of the AISC bracing business. Just general basement wall stability issues.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[hines86]

Perfect exactly what I was looking for. I am just trying to put numbers behind what is allowed by code. I know code is based on performance, but if it is performing and we don't get the numbers to work, we are missing something. I really believe the stiffness of the material/ connections is what gets overlooked for simplicity. I will run the model and let you know. We are definately on the same page. Thanks.