Existing Pre-Engineered building foundation

[red22]

Good day all,

I am working on a project involving a pre-engineered steel building and an existing foundation. The concrete footings/foundation is in place and the steel frames are erected. I was called in by the owner to review the design and construction after some issues were noted during the building erection. The building is 250' long with 160' clear-span between columns. The issue has only to do with the foundations. I have a foundation plan prepared by another engineer, however the construction does not match the foundation plan. I have performed a visual inspection and we have also performed GPR (ground penetrating radar) testing on the footings. The GPR results showed virtually no reinforcing in the footings, however readings could only be obtained up to a depth of 20" +/- (the footings are 6' wide x 16' long x 24" +/- thick). Top reinforcing in the footings is not necessarily required, however bottom footing reinforcement is a key issue and cannot be identified. Does anyone have any suggestions as to verification of footing reinforcing or any other approaches I can look at before we take the building down and start over? Any possible repair procedures for post-installed reinforcing?

Thanks,
Bob

 

[CANPRO]

I don't know exactly how GPR works, but can you remove 4" of concrete in some areas so that you can get a reading to the bottom of the footing? I couple spot checks might give you some confidence in what is there...

 

[charliealphabravo]

You could do destructive testing on a footing that is not being used in the new plan if there is one.

Short of that you could put several cores into the main footings to see if you can intercept any steel.

I can easily understand that the top steel might have been omitted by hook or crook, but if there is truly no bottom steel then that would put the quality of the entire foundation into question I think.

My only other thought is that in areas with high lateral loads, the foundation is carefully matched to the building system... particularly if there are any wind columns in either the original or new plan. I would think that the new building system would be more forgiving and adaptable to an existing foundation if cable x-bracing were being used rather than wind columns for the lateral load resisting system.

 

[ajh1]

With no reinforcement in the upper part of the footing you need to make sure that either your anchor bolts are well away from the edges of the footing, or are deep enough to intersect with the assumed lower reinforcement steel. A 160' clearspan frame is probably going to exert more force horizontally into the footing than vertically, or at least it will seem that way when the footing breaks and the base of the steel column is now 6' outside of its original location.

 

[ajh1]

Bottom line:
If the actual construction does not meet the approved plans, you've got a big problem and it should be on the foundation contractor to make it right.

 

[red22]

Thank you all. The problem I have is verification. The quality of the remainder of the foundation is questionable as well. Destructive testing would only verify one location or perhaps a couple, I am not sure I would feel comfortable assuming the remainder of the footings are acceptable based on just a couple cores. The horizontal reaction at the base of the column is about 100 kips, downward vertical about 100 kips and uplift about 20 kips. Unfortunately, the original contractor has been terminated and it is now my responsibility to make sure we have a safe, code compliant building.

 

[JedClampett]

The contractor had to order bars. Make him show you the reinforcing shop drawings and invoices. This doesn't prove that they were installed, but if they didn't buy any bar, it proves it wasn't installed.
I would be caseful about any retrofit fixes on a new building. Make the contractor disassemble the metal building and redo the foundation. You're going to be in a very hazy area of responsibility, with the vast burden falling on you. In other words, if the HVAC doesn't work right, they're going to come to you.

 

[hokie66]

At the least, I would want to remove one complete footing, take it apart and see how it was built. Then compare that with what it would take to resist the forces you have. How was the horizontal thrust to be resisted? Uplift?

 

[dik]

16' long?

Dik

 

[dik]

If soil bearing approx 3 ksf... then 6'x6'? May work as plain concrete, without any rebar.

Dik

 

[red22]

The lack of quality in the as-built foundation is like nothing I have seen before. Even if we were to dismantle one footing, I don't think I would be able to assume that all the other footings are the same. Horizontal thrust is going to require the installation of tie rods and there is enough mass in the footings to resist uplift forces. There are a number of footings with significant eccentricities between the cl of column and cl of footing. These will not work, and will require removal and replacement (or addition of concrete and reinforcing.

Dik, I have thought about checking the capacity of the plain concrete section, but based on the overall lack of quality, testing reports etc. with this job, I am not so sure. There are still a number of unknowns. Would you design a footing for this size structure as plain concrete?

 

[lsmfse]

Was there no building inspector?

 

[hokie66]

Plain concrete, no. And to resist uplift, you need top reinforcement.

 

[red22]

Let's just say the building inspector could have done a better job.....

hokie66, I have never designed an unreinforced footing for something of this scale, although, per code, I guess it is acceptable. I checked the requirement for top steel based on the plain concrete section, and it works, so top reinforcing would not be required. Not sure why I am having such a hard time convincing myself about the bottom steel....

 

[dik]

I wouldn't normally use plain concrete for that size, but, if I were checking an existing condition I would likely accept or at least sleep easier... I have checked an old existing armory that used two pad sizes of plain concrete (it was constructed in 1913) and had no difficulties; they were slightly larger. The smaller pad was supported on a larger pad... both being 16" thick...

Hokie... as long as the anchorage into the plain concrete is adequate, it doesn't matter much which direction the force is... just a little more concentrated at the rebar... and makes for a slightly greater moment arm.

Dik

 

[MiketheEngineer]

RUN - don't walk away from this one!!

 

[woodman88]

Could they dig down at the sides of the footings to check (with the GPR or cutting the footing at some locations) from the sides to see if there is reinforcing within 20" from each side at the bottom?

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[BadgerPE]

"RUN - don't walk away from this one!! "

While I don't disagree, isn't there an ethical obligation to ensure that the project is brought up to par since Red22 is already aware of some potential deficiencies? I guess maybe that means notifying the local building authority, but that doesn’t mean it won’t fall through the cracks somewhere.

I am no way calling you out for your statement Mike, but I just wanted to see what others thoughts’ are on the subject. I am a fairly green engineer and am just merely being inquisical.

 

[ztengguy]

Where is the original engineers calcs, or where is he? why is he not being engaged to figure out if what the contractor did is acceptable? I agree, run, or do what you have to do to make sure you would feel comfortable taking responsibility, it seems like you are going to end up with it on your shoulders.

 

[msquared48]

I would do destructive testing on one or two footings, and make my determination AS A LICENSED STRUCTURAL ENGINEER, from that analysis. If there is no reinforcing as suspected, tear it down. If there is, do the calcs and see if f the steel that was furnished was sufficient. As an SE, you DO have the power to make this decision and put the burden of proof on gthe contractor to show otherwise. It is a life safety issue if the building is under-reinforced.

You will have to make a decision based on a little information here showing a GENERAL tendency.

What was the original contracgtors reputation? Any similar problems in his past? Did he have money problems? Has he had any complaints or bond forfeitures in the past?

You, or your client's attorney, need to do further due dilligence and ask a few questions.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com