Old Design flaw, what to do.
Old Design flaw, what to do.
(OP)
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?
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?





RE: Old Design flaw, what to do.
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.
RE: Old Design flaw, what to do.
RE: Old Design flaw, what to do.
Mike McCann, PE, SE (WA)
RE: Old Design flaw, what to do.
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.
RE: Old Design flaw, what to do.
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 ....
RE: Old Design flaw, what to do.
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.
RE: Old Design flaw, what to do.
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.
RE: Old Design flaw, what to do.
RE: Old Design flaw, what to do.
RE: Old Design flaw, what to do.
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.
RE: Old Design flaw, what to do.
...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.
Mike McCann, PE, SE (WA)
RE: Old Design flaw, what to do.
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.
RE: Old Design flaw, what to do.
RE: Old Design flaw, what to do.
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
RE: Old Design flaw, what to do.
Dan, not at all. Your points are valid. And welcome to Eng-Tips.
RE: Old Design flaw, what to do.
RE: Old Design flaw, what to do.
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?
RE: Old Design flaw, what to do.
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)
RE: Old Design flaw, what to do.
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.
RE: Old Design flaw, what to do.
RE: Old Design flaw, what to do.
My main concern is what to do about the existing building. I’ve been working to come up with a fix to have in-hand before speaking with the owner, but it's proving difficult. The building is presently in use and with the columns in the walls, I’ve been trying to find a solution to minimize the demolition and limit it to above ceiling work if possible.
The required braced length is 14’-6” for 4 columns, and 12’-6” for the remaining two. So, my first thought was to use angle braces off each face of the column, at the required elevations. The angles would go up to the beams/joists and be bolted to gusset tab connections at each location.
Unfortunately, in most cases there is large ductwork at the sides of the columns at the elevations that I need the bracing, leaving me with access to only two sides of each column. Is it feasible to provide T/C angle brace bolted to a gusset in two orthogonal directions and consider the column braced at that elevation? Or would I be inadvertently adding moment into the columns and doing more harm than good?
RE: Old Design flaw, what to do.
RE: Old Design flaw, what to do.
RE: Old Design flaw, what to do.
RE: Old Design flaw, what to do.
RE: Old Design flaw, what to do.
As you have solved the ethical part of this, perhaps you should formulate a new thread in the Structural Other Topics forum.
RE: Old Design flaw, what to do.