Old Design flaw, what to do. 4

[NinerStruct]

I recently started work on a site-adapt project for a public building that has already been used on another site. The structural engineer that did the previous design has since retired and I was tasked with the structural design of the new building. I rechecked the calcs from the previous engineer's design and did my own design when I couldn't find the original.

When redoing the design for a few columns, it appears that they were under-sized in the original design. The worst column is an HSS4x4x1/4 located in an area with a roof height of 19.5 ft, and a maximum unfactored design load of 62.5 kip. So my design says that it should be an HSS6x6x1/4" if there's no bracing provided.

The original building is over 10 years old now, and there hasn't been any failure. I'm guessing that's because a)it hasn't seen the full design load yet and b) the columns are buried in light gage walls that are likely providing some lateral bracing. Now, I don't imagine that the previous engineer had purposefully counted on non-structural walls to brace the column, but I can't find the original calcs for these. Either way, it's not something that I'm comfortable doing, so I'm changing them in the new design. Which leaves me with the question:

What should I do about the existing building with 4x4 columns already in service? Should I be notifying owner about this? Should we be coming up with a fix for these columns?

 

[JedClampett]

Once you're 100% sure that you're right, you absolutely need to tell the owner. You need to do this using some method that is recorded, like registered mail. Note that you probably want to warn him that this is coming, not surprise him.
As it says in ASCE Code of Ethics:
"Engineers shall hold paramount the safety, health and welfare of the public and shall strive to comply with the principles of sustainable development in the performance of their professional duties.....
d. Engineers who have knowledge or reason to believe that another person or firm may be in violation of any of the provisions of Canon 1 shall present such information to the proper authority in writing and shall cooperate with the proper authority in furnishing such further information or assistance as may be required."
I wouldn't name names, or cast stones, just matter of factly tell the owner that you've found some overstresses beyond the code allowables and that these need attention. You can offer to design the fix yourself or recommend another engineer.
I wouldn't jump to the "proper authorities" until it's a last resort.

 

[hokie66]

Jed is correct, and his advice is right on target.

 

[msquared48]

I would try to contact the original engineer of record and relate your concerns to him (or her). Might answer some of your questions, particularly considering the marginal possibility of getting a copy of the original calc set from him (or her).

Mike McCann, PE, SE (WA)

 

[ornerynorsk]

This thread reminded of the Citicorp Building.

http://www.damninteresting.com/a-potentially-disastrous-design-error/

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[racookpe1978]

So, what is your recommendation/requirement for fixing the columns?

Also, is the building "safe to occupy" until the changes are made? "Safe for use" but not for storage of heavy material on the second floor? Safe, but not for people on the second floor? Safe, but would not withstand a code earthquake occurring at the same time that a tornado passes overhead?

Obviously, it has not collapsed in the years after construction. But ....

 

[NinerStruct]

Thanks again for the additional replies. After rereading my original post, I realize that it may have come across somewhat like Chicken Little in that I did not give enough detail to explain that this is a single story building. And, while not trying to undersell the possible importance of the issue, this is not a multi-story building and is not an issue of the same magnitude of the Citicorp building. These are interior gravity only columns that are supporting a bar joist/metal deck roof, and they're fairly lightly loaded. The building isn't in any danger of immediate collapse, as there's no snow load currently and it's been through ten winters without a problem.

However, after running the calcs on them, even with paring down the assumed dead loads to what is actually there, these columns appear to be undersized. If they ever do see their full design load, there's the possibility of buckling. I'm meeting with the original engineer next week to make sure that I'm not overlooking something, and it's possible that they added some sort of bracing during construction and that it wasn't on the documents, I don't know. So hopefully he can help shed some light on this.

 

[racookpe1978]

Hey!

Chicken Little was right!

He (she ?) WAS hit on the head with something unexpected and potentially dangerous in a supposedly safe area. Now, her conclusions AFTER being hit on the head by an actual object were excessive, but they were actually correct IF her conclusion that the "sky is falling" was right.

So check your calculations and verify your will be hit on the head by a tree limb, but not the whole tree. Then, go get the tree limb trimmed off or roped up properly.

 

[hokie66]

What's your point, racookpe? NinerStruct has this under control.

 

[MrHershey]

Another item to look at, though not necessarily hang your hat on. May want to see if the older engineer still has the mill certs for this job. Just finished reviewing a bunch of A500 B/C mill certs for a job and the vast majority of them were ~20% stronger than required by the ASTM. Just a thought.

 

[Ron]

Niner...a few things to consider, even though I agree with your approach at this point.

The building was obviously designed under different code provisions than currently prevail. Depending on which code that was, there is probably a lot of latitude in engineering judgment. As an example, the building you described, over ten years ago, could have been designed under one of two prevailing codes in my area. One is a national standard (ASCE 7) that was not mandatory for such buildings...the other was the Standard Building Code which was much more vague in load application. Further, codes are really fickle on defined geographical areas. Wind isotachs change location, snow isobars change location, and seismic zones get redefined (happened this week in the US). These are all things that hopefully a discussion with the original engineer will clarify.

Outside all that, your obligation is to the current state of the practice (standard of care), so recommend to the owner what you think is necessary for the protection of the health, safety and welfare of the public. The "how" of what is currently in place becomes less relevant when you know you need to upgrade the structure.

 

[msquared48]

I emphasize what Ron said here... with a little selected editing for extra emphasis...

...so recommend to the owner what you think is necessary for the protection of the health, safety and welfare of the public (. The "how" of what is currently in place becomes less relevant) when you know you need to upgrade the structure.

In other words, don't give the owner a heart attack until you know that he needs to have one. Make sure he pays you first...

Mike McCann, PE, SE (WA)

 

[hokie66]

NinerStruct,
I think some here are missing the point. This is not about any change in codes, or grade of steel, or payment for services...the simple fact is that you have discovered an existing column which is entirely too slender. It has to be fixed, and because you know it, you are doing the right thing in addressing it...expeditiously.

 

[Ron]

hokie66...didn't miss the point. I agree; however, when told, the owner will want to blame someone. My point was simply there might not be anyone to blame so move on with the fix.

 

[kd5det]

Forgive me if I am asking really stupid questions or am out in left field. I am a PE Civil Engineer but not structural. Most of my experience has been as an owner's representative for building design and construction.

Are you using the design drawings, the shop drawings or the as-built "record drawings"? I would not get too excited until I verified everything in the field.

Nothing is ever built exactly as the issued design drawings or shop drawings. Record or as-built drawings are never complete. I would never assume too much from old drawings etc. unless I was sure that I had all communication issued during construction including Shop Drawings, RFI Responses, Amendments, Addenda etc.

I have had experience where the construction administration was done well and I have seen it done in a completely slipshod fashion. I have seen design errors caught during construction and properly corrected but only documented in addenda and meeting minutes. There is no substitute for detailed on-site verification.

You may have done this but you only mentioned checking the design calcs.

I am new to eng-tips so I hope I have not been too much of a smarta$$.

Dan McLaughlin

 

[hokie66]

Ron, he did say in his second post that he has arranged a meeting with the original design engineer. Good move.

Dan, not at all. Your points are valid. And welcome to Eng-Tips.

 

[Ron]

Dan...welcome. We're a strange lot, but generally good. Smarta$$ comments expected!

 

[NinerStruct]

I really do appreciate all the feedback. On it's face, this almost seems like a dumb question: "Should I tell the owner if their building is deficient or not?" but as many of you have pointed out, there's a lot of latitude in how things are designed and where engineering judgement comes into it. So it's helpful to have this discussion.

Before I spoke with the engineer, I relooked at my numbers and pared them down where I could to make sure that I wasn't being too conservative, I even looked at trying to account for the column base to be considered fixed, but really the only thing that can make these columns work is whether or not they're considered braced or not.

Anyway, I spoke with the engineer this morning and he indicated that he counted on the full-height wall studs to provide bracing. He said that he believed the adjacent studs were tack welded to the column to help provide the connection. He couldn't remember on this specific project, but said that he had the conversation with light gage installers a number of times before. So he didn't see a problem with considering the column fully braced. I could not find anything in the specification or drawings that would indicate one way or the other whether the studs were welded, but he said that it was a common practice, and part of good construction practice to connect studs to the columns. I haven't used non-structural walls for bracing, so I can't say that I've paid particular attention to stud attachment to columns, but in my experience I don't believe welding of studs to columns is too common. Also in my opinion, the walls would provide bracing only in one direction (in the plane of the wall) at best without the column being located at the intersection of two orthagonal walls. I have a great deal of respect for the original engineer, but I don't believe these columns to be adequately braced.

So now a new wrinkle has emerged; being as I don't believe these columns to be adequately braced, in the new building, my proposal to the architect was to change to 6x4 columns with angle bracing in the weak axis (large ductwork prohibits bracing in both directions). Unfortunately, the new project was already in the shop drawing phase before this came up, so this proposal would likely incur a change order. Now the architect is concerned the owner will question why this is needed, or if the original building is unsafe, putting them in between two differing opinions.

Am I being too conservative by not counting on the walls for bracing? The columns are buried in full height non-structural walls, and there is a hard ceiling at about 12'-0" on one side and a drop ceiling at about 10'-0" on the other side. Should I stick to my guns regarding my project and say that the other building wasn't my design if the question is brought up?

 

[msquared48]

Personally, I would never use a non-structural demising wall for lateral bracing. These walls can be removed during any TI, eliminating any possible lateral bracing, and I doubt there would be any explicit directions on the drawings, which were probably lost, to keep the wall(s) intact.

I would contact the original engineer again, as a matter of professional courtesy and explain your concerns and where you see that you have to go with it. Depending what he says, contact the owner and let the chips fall where they may. Anything less and you will be taking some of the blame should any failure occur.

As previously mentioned, have a fix in your hand...

Mike McCann, PE, SE (WA)

 

[hokie66]

I agree with Mike that non-structural walls should not be used for bracing structural columns. Period. I would not depend on bracing parallel to the wall, and certainly not perpendicular.

You just need to advise your architect that 6 x 6 columns are required. Change orders happen all the time, especially in the modern way of proceeding without adequate information. If the architect is reluctant to properly advise his client, then you should request/demand a meeting.

You have received the opinion of the retired engineer, so I would not bother to contact him again unless the owner requests.

A quick thumbnail look shows these columns have only about a third of the required capacity. So you have a duty to the "public", not just to the client and architect.