Everyone Says the Structure is Overdesigned 8

[epitome1170]

So the common theme in today's construction/engineering industry is for the contractor to tell the owner or architect that the structural engineer has over designed the building and is just being conservative. This happens a lot whether you are designing it per code or adding in some conservatism. So how does your firm address these concerns?

Just recently in my area I have had the good fortune of adding additional clientele due to their previous E.O.R. getting so frustrated with the GC that they told them off. Obviously, the GC did not take too kindly to this and so are using my firm for their business instead. My approach when the "over designed" discussion takes place is to try to discuss new implementations of the codes and the loadings. This usually alleviates some of the tension and allows everyone to get back on the same page.

So how does your firm do it?

 

[TXStructural]

The quote I heard the other day was: "Anyone can design a building to stand up, but it takes a structural engineer to design one that just barely stands up."

Designing according to code is the MINIMUM design. For most structures and occupancies, the loading and design elements required by code will be conservative (typically by 40% at full design load, and then few structures see the full design loads), but the code is why we have seen very few structural failures in the US. Just look at the collapse today in Bangladesh for an example of construction that was probably "almost adequate" for quite a long time.

I have met engineers that design on the cusp of code compliance because of what I call "fear of future VE" - they cut every corner to reduce what might be perceived as over-design. The result I saw while doing forensic structural work was serviceability problems that resulted from failing to consider everything in the cost cutting.

The thing that I am hearing from larger contractors is that engineers need to simplify designs for constructibility, rather than trying to save every pound of material. Save the complexity for the places that require it. Reduce the number of beam and column marks, making repetitive things as uniform as possible (don't make them similar when they can be the same.)

And ultimately, we have the education, experience, and licenses to do engineering. It is our responsibility to properly apply the code and design the proper structure.

 

[JoshPlumSE]

There is a saying that I've heard a number of other engineers repreat which I might use in these situations. Something along the lines of:

I can give you two of the three: Reduced engineering cost, reduced schedule, or reduced construction cost.

 

[dcarr82775]

I always tell the contractor that I over design things so that when they screw things up and don't build to the drawings it doesn't fall down.

 

[TLHS]

If there's a serious concern, I've gone through and justified things in the past. You should generally be able to justify any of your design decisions. It's normally not worth it if it's just the contractor complaining, though. The contractors are almost always going to complain.

If it's just idle complaining, I'll generally start babbling on about one tricky part of the design. Seismic is great for it. Everyone knows seismic provisions are the current target of a lot of code development, plus a lot of people don't understand it. So if you start going on about ductile moment frames and R values and how you've avoided detailing requirements to simplify construction and things like that they'll run out of things to say.

 

[1gibson]

Well of course the contractor will say it is overdesigned, how else will he explain to the end user why it ends up costing more than his original bid?

 

[jgailla]

I'm in civil, but we get the same complaints on design-build jobs and to a lesser extent on design-bid-build jobs. For design-bid-build jobs, if you know their suggestion is ridiculous, just smile and nod.
If you are confident that your design is good you should be able to explain design decisions to the contractor and they should back down.
I expect questions on a design-build contract. A good GC will accept a good explanation and not press you to push the rules. The last one I worked with was good. They confronted me about many design changes and cost savings. In some cases they were correct and the additional cost was unwarranted. In most cases no savings could reasonably be realized. As long as I had a good argument they dropped it. If I didn't have a good argument I'm wrong anyway.
If you are working with a contractor who will back down when presented with evidence and reason, good. If not, you need to stop working with that client. They will stab you in the back when it becomes expedient because they are fundamentally dishonest.

 

[dhoward26]

I usually pull out the code sections and supply the contractor with the calculations and reasons to back up what I'm doing and have discussion with him on it until he is content. It's very easy when you have the code and a few numbers to back you up. Plus, it shows the contractor that you are actually taking the time to address his concerns and follow the code to keep both of you out of trouble in litigation.

 

[paddingtongreen]

I haven't had it often, but once my reply was, "Fine, come in here on Monday and show me how to design the structure and I will come to you on the following Monday and tell you how to build it."

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[StructuralEd]

We've had tremendous uncharacteristic snow storms in the past few years and NO one ever mentioned overdesign. all hoped for it.
It's funny that those contractor's who are quick to condem designs are the ones who say "we're just contractors, not Engineers" when something goes wrong.
The wiser, more experienced contractors don't go down that road and stick to their part of the process; constructing.

 

[drawoh]

The quote I heard the other day was: "Anyone can design a building to stand up, but it takes a structural engineer to design one that just barely stands up."

Perhaps you saw it in response to one of the photos I posted in Pat's pub.

thread1088-343440

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JHG

 

[SteelPE]

I've heard that quote once on a PBS/NOVA program called "Super Bridge" which was broadcast in 1997. They were interviewing someone involved with the construction of the bridge and they said "Anyone can build a bridge, but it takes a true craftsman who can build a bridge that barely holds the weight required."

 

[paddingtongreen]

"The quote I heard the other day was: "Anyone can design a building to stand up, but it takes a structural engineer to design one that just barely stands up."

This is akin to the pursuit of Adequacy. The problem is that if the structure had no problems it must have been overdesigned compared with the adequacy target, so we must design tighter next time.. ..and on until a structure tells us that we have gone too far.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[dhengr]

The structure is always over designed if it is still standing, never mind that it has never seen it max. code design load yet, and it will most certainly be your fault if and when it ever fails. So, be very careful how you comply with what others wish for.

These comments about our structures being over designed probably has less to do with a few extra pounds of materials used in building the structure, or the extra time we spent trying to refine the design; and much more to do with the complexity that so many of us (or our clients) are introducing into our structures. For good reason contractors like simplicity and repetitive details, member sizes and spacing, etc. With the advent of CAD and the various computer software, we can draw and design things which are very difficult the fabricate and build, and we don’t give that part of the process a second thought. We can design conc. beams in increments of 1" or .5" in depth, but then imagine the contractor farting around with new forms for every beam or the rebar faber. screwin around with different height ties for every beam, and then finally sure as hell the field guys will install the 16" ties in the 15" deep beam and not notice it until they are pumping conc. All to save an inch of conc.

Then, we seem to be having fewer and fewer experienced engineers doing and overseeing this part of the work, and more young engineers being able to tackle more complex designs without any, or enough, good guidance and mentoring on the whole process. Just consider many of the questions we see here on E-Tips, questioning much minutia, either code wise or detail wise, but the very nature of the questions suggests that the OP’er has very little understanding of the whole big picture. And, they apparently have no one to go to with their questions, or to gain a better understanding of the entire thought process of design; no one to draw them a sketch or explain that the change in weld detail on this one joint will cost many times, in detailing, layout, welder time, inspection and potential error, what might be saved in weld metal. And, the way we are approaching building codes and using computers for our design just contributes to this problem.

 

[focuseng]

Some say the glass is half empty. Others - half full. The engineer looks at the glass and says it has a safety factor of 2.
The contractor may be correct but he is also very wrong because he doesn't know what the safety factor is at all or what it should be much less how much water is actually in the glass.

______________
MAP

 

[MrHershey]

Have generally gotten around it with the usual contractors by compromising. Will try to work with them to massage details or perhaps refine some things. For example, some contractors seem to like a very small number of column types to minimize the chances of them screwing up, even if it means a lot of the columns are vastly overdesigned. Others are confident they can get it right and like things to be more refined to lower the material cost. Same goes for shear wall reinforcing as you go up the building. Some guys want same wall thickness and reinforcing top to bottom or maybe just two or three variations. Others don't mind having different reinforcing each floor, within reason. Obviously some of these aren't as easy if the job is bid out (instead of negotiated ahead of time or design-build). Have had some success just explaining things to contractors too. Explain why certain elements are needed here and not there, why the reinforcing is so heavy here and not there.

Just generally try to be helpful and understand where they're coming from, while firmly holding ground on what you need to hold your ground on and yielding a bit where you can yield.

 

[WARose]

The last time I got in that argument with a contractor…..I got so irritated I sent him my calculations (which included STAAD output and so on) that proved I was utilizing as much as 95%+ of the structure’s capacity…..I then told him: “Ok, so tell me where I’m going wrong.”

Another good one recently is with a manufacturer we work with…..he was so convinced I was wrong about an existing structure he said he was going to ask a “3rd party” who apparently was an independent consultant (structural engineer). I (politely) told him: good, he’ll tell you the same thing I just did. Sure enough, Mr. 3rd Party not only backed me……but said he wouldn’t mess with what I was doing for any amount of money. Classic.

 

[JoshPlumSE]

Remember that the contractors only see the construction side of it. So, they can be right and wrong at the same time.

In the late 90's a friend was approached by a home owner who was getting the "I've been doing this for 30 years and I've never seen an engineer do blah blah blah...." from his contractor. He didn't like the steel moment frames around the garage door openings.

My friend looked over the drawings and calmly explained, "I'm sure he's right. We've been doing it differently and less expensively for at least 30 years. Then the Northridge earthquake happened and people died. Now, we do it differently." All that was needed was a simple explanation to the contractor and /or owner about WHY the design looks different than what they were expecting.

 

[Once20036]

I appreciate this discussion, but get a kick out of the original posting saying, "...the structural engineer has over designed the building and is just being conservative. This happens a lot (when you) add in some conservatism." (clearly edited for emphasis)

Recently I had a client complaining about a slab on grade I designed. He had a tall racking system with 30kip post loads that he wanted to put on a 7" poly fiber reinforced slab. I called for it to be demo'd and replaced with a reinforcing 10" slab. He went on and on about how he had other warehouses with heavier loads and thinner slabs that were just fine.
I told him I couldn't put my reputation on the line just because he had been lucky in the past, and offered to investigate his existing slabs so I could explain what the differences were.