Urgent Help Required

[dik]

This was picked up on SEAINT:

Fellow engineers,
A colleague of mine, a registered P.Eng., is facing a discipline committee hearing regarding the suitability of one of his structural designs. He has asked me to sit in as an expert witness on his behalf and I have agreed to do so. One of the key issues will be the suitability of the use of concrete nails in securing a double 2x6 "post" to a concrete foundation wall. To help me prepare for this role I would appreciate any comments you are prepared to send.

The situation details are the following.
The hearing date is May 13, but some documents must be filed by May 6 (not yours, of course).

The project is standard residential wood frame construction.
The house is a single family "split level" located in south/central Alberta. Seismic is virtually zero; wind is fairly high; but neither of these are applicable to the case. Usually a structural engineer is not involved with a single family residence in Alberta unless there is some special circumstance such as an unusual beam arrangement, a retaining wall, or some problem such as the one I am describing develops.

The floor system is 2x10 floor joists supported on laminated
wood beams (possibly MicroLam or ParaLam both of which are made op of approximately 1/8" laminations with the glue plane vertical and totalling 3.5" in width) which are, in turn, supported on columns. Normally, there is a pocket cast in the foundation wall to support the end beam beam reaction; but on this project the pocket was omitted,
hence the problem.

The foundation wall is 8" thick; the strength and age of the
concrete are unknown. Normally, concrete strength would be about 2,500 p.s.i. and it could be normal or sulphate resistant. One may speculate that the concrete age might be from 5 to 15 days. Below the wall is a footing 6" thick and 16" wide. There is no requirement for reinforcing steel in residential concrete basements although some builders place ten millimetre or #4 bars horizontally at 15" centres.

Since the beam pockets were omitted my colleague got involved. His solution was to place a 2x6 "on the flat", against the wall and nail it to the wall using ten 5" long by 3/16" diameter concrete nails. He then took a second 2x6 and nailed this directly to the first using "an appropriate number of ordinary wire nails". This provides a 3" seat for
the laminated beam. The double 2x6 are approximately 5' long or less and are also in contact with the wall's strip footing. The slab on grade basement floor is placed directly on top of the wall footing encasing the double 2x6 post. Unless I have been misinformed there has been no indication of a failure taking place.

Please comment on a) the suitability of using concrete nails in this way, b) the capacity of such nails, or c) anything else related to this situation you want to. All replies will be appreciated.
Thank you.
Regards,
H. Daryl Richardson


My Reply:
I picked up your request in the SEAINT; Is there an opportunity to get an extension in time? The short notice is not much time to get a response.

As I understand your post, the 2-2x6 are supporting a paralam floor beam with end grain bearing of the 2x6 in contact with face grain bearing of the paralam. The 2-2x6 are restrained in both axis and the load is transferred directly from the beam, through the 2-2x6, directly to the footing. Is this correct?

Are there any dowels between the footing and the wall. 6" of plain concrete is a little thin, but can have some strength. Do you require the concrete nails to provide any vertical resistance to reduce the load on the edge of the footing and redistribute it to a greater portion of wall?

I've taken the license to post this on another group (

http://www.eng-tips.com)

along with your email address in the form of 'h.d.richardsonatshawdotca'.

 

[BigH]

I'll keep this short - unfortunately no comment on the technical side - I would love to know who (i.e., position) put him up on charges if there is no failure, no indication of failure. Who is worrying about this - a building inspector? Good luck - and I am really surprised, from what you've stated, in that this got this far along.

 

[dik]

Agree...

 

[VAD]

When this sort of problem occurs building inspectors look for reasons why something different was done. Generally, if this concept in remediation is not liked one would be told before passing this to the disciplinary committee. Having read many of such reports this has been my impression. I would want to check the Alberta building code regarding the use of nails into concrete. Generally, I have experienced that they do not always hold well even when you try to nail horizontally on a concrete floor. The other aspect is the spacing of nails and the depth of embedment. In any case,if you are going to do something different than what the code stipulates then you should have the information to substantiate your change. I would suspect that there is a bit more to this event. Is there some thing else occurring that the home owner is not satisfied about. Have the 2 by 6 members split when nailed or were they predrilled. I suppose the latter was done.

It would be prudent to check a few clauses in the building code. If Alberta, Check 9.23.9.2. The question that failure has not occurred is not generally the answer for the building inspectors. There is also the question of compliance certification if the house is going to be resold at any time.

It is often wise to check with the building department to ensure that what you are doing is on the right track. If in doubt they will also ask that you stamp the drawing of the remedial work. Again, if they think it is faulty they would ask first that you rectify before going to the extent they have.

Good Luck

 

[dik]

I agree also that just because it hasn't failed isn't a good argument and the remedy may have been 'hasty'. I haven't done any sums...

My experience with powder actuated fasteners has been pretty good, for lower strength concretes. Also, the force required for maintaining stability is usually small and the fasteners provided would likely be more than adequate.

Lumber in the longitudinal direction is relatively stable and on the interior of a building, there should be no tendency for the member to swell and work the concrete nail out.

I don't have a copy of the Alberta Building Code, but have passed the response on to Richardson.

Thanks, Dik