Dumbest thing an engineer ever did 11

[RontheRedneck]

A while back in the thread I started about engineers being wrong someone asked me to post something like this.

We sent out some trusses that needed to be field spliced. Huge 3/4" plywood gussets.

The framer called me and asked "What's the tolerance for the cuts on the plywood gussets." No one had ever asked me that before. So I told him I'd call the engineer who drew the splice detail and ask.

I made the call and asked the question. The conversation went something like this:

There are no tolerances.

What do you mean?

There are no tolerances. The cuts have to be right.

The cuts will be made by humans with hand-held saws. There have to be tolerances.

No, there are no tolerances. Tell them the cuts have to be right.

When they make parts for the space shuttle there are tolerances. Everything has tolerances.

No, there are no tolerances.


I eventually figured that the conversation was about as painful and unproductive as beating my head against a tree. So I gave up.


In my entire career that is the most ridiculous conversation I have ever had with an engineer.

 

[Enable]

I'll be honest: I probably did at least three things dumber than this in the past week.

 

[driftLimiter]

Engineer could have said "Minimum edge distances are shown on the drawings"
Ron could have said "Same tolerance as the truss industry XXXX"

I can see how the engineer bottling up and sticking to his guns that "There is no tolerance" is ridiculous.

In general I think my wood construction details could benefit from more use of "Min" , "Max" dimensions etc. This is really what we are after.

When I design a gusset I don't care if it is cut within 1/32" of the shape I drew. I care that there is enough edge distances to fasteners, enough cross section, etc.

 

[JStephen]

The key for the "no tolerance" cutting is to use the proper measuring equipment. It's been a long time, but as I recall, the rulers we had in First Grade showed inches but no fractions, and those would have been ideal for this application.

My brother used to work for a company that made pacemakers. So this was all high-tech must-be-right medical stuff. Those pacemakers came with a wire lead, which the surgeon would cut to length when he installed it, so it didn't really matter how long it was. But, being that application, the length was prescribed with great precision anyway. So the motto for those leads was "measure it with a micrometer, mark it with a piece of chalk, cut it with a hatchet".

 

[chris3eb]

Structural engineers don't generally specify tolerances. My guess is that the engineer interpreted your request as "how much smaller can I make this?" and their response was meant to mean "don't make it any smaller than specified." It may not have even occurred to them to say -0", +1/2" as Pham mentioned, because it would seem so painfully obvious that a gusset having a little extra meat wouldn't be an issue.

Another general thing with structural engineering is that we get asked all the time what is the smallest/biggest something can be. For most things, there is a range from "definitely ok" to "definitely not ok" with a huge gray area in between. We try to specify things in the "definitely ok" range. Once something is built, if it is not what we specified and is in the gray range, we can decide whether or not to accept it. But it's really difficult to determine the exact line between things we would accept or not.

 

[AaronMcD]

I sometimes get asked about tolerance on something. Usually I don't really care, or don't know, so I just pull a number out of my ass that I know will work and will feel reasonable to the contractor.

It's really only when they don't ask for tolerances that I go to the site and see something wildly off.

http://www.hellodwell.design

 

[Lomarandil]

I'll be honest: I probably did at least three things dumber than this in the past week.

Yup... I'm there with you

 

[SWComposites]

THIS is the problem that many engineers now have NO experience at all with making things themselves at home, much less any real world experience building things or working in a factory. They think that things are made perfectly, since in the CAD model everything fits together exactly. SIGH. Its already bad and getting worse with engineering being outsourced to places half way around the world.

 

[struct_eeyore]

Second hand account from my old boss. This takes place at a local SEA meeting in Florida.

Presenter is giving a speech about wind loading and the difference between ASD and ultimate.
Presenter says something along the lines of: "as you know, in order to convert from ultimate to ASD, you must divide by sqrt of 1.6.
Engineer in question says something like: "No, you divide by 1.6".
Presenter and group corrects him.
Engineer says: "Welp", and walks out of the meeting.
Supposedly he disappeared after that.

 

[RPGs]

A long time ago I tried to build a small wooden target stand. The range required you bring your own and it had to be a certain height. I thought I'd be fancy and give it a few hinges so it could fold up. Drew it in cad and laid out all my cuts and bolt holes. The darn thing was hilariously crooked and the holes hardly lined up and had to be enlarged a stupid amount. Embarrassing and eye opening experience for me. I have a lot of respect for good carpenters.

Funniest part was when I got to the range I noticed everyone else was much smarter and made theirs out of simple PVC pipe. I must have looked pretty silly hauling out my huge wooden folding mess and struggling to set it up during cease fire. It also got shot to bits and splintered so badly I had to just throw it out after a few uses.

 

[phamENG]

Had a friend several years ago who bought a new door for his house, and spent an inordinate sum on it. Of course it was custom and not refundable, and he bought the wrong size. So he called me for help and we set to work enlarging his door frame. Not easy in house with brick veneer and not an ounce of know how between us for messing with brick. (I'd tried once and it was a miserable failure, so I didn't volunteer.) After battling it for hours late into the night, we finally got it in. There was no room for shims.

He had that end of his house redone recently and when they pulled the door and installed the new one...apparently the carpenters all gathered round to marvel at it. They measured and found that we had that door frame square to less than 1/32" and only about an 1/8" clearance all around the door frame.

 

[dik]

Never sand... always use a chisel. A few thousandths is big... a lot less than that... a snug fit without tapping...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Tomfh]

You’re doing alright if an engineer demanding perfection is the worst you’ve dealt with.

The best ones I’ve heard recently are:

*An engineer who neglected to add the weight of the water to the rooftop pool design. Things started to happen when the pool was being filled.

*The engineer who’d modelled the self weight of the giant hanger doors as acting in the horizontal direction. Upon installation the doors failed.

 

[human909]

The best ones I’ve heard recently are:

*An engineer who neglected to add the weight of the water to the rooftop pool design. Things started to happen when the pool was being filled.

*The engineer who’d modelled the self weight of the giant hanger doors as acting in the horizontal direction. Upon installation the doors failed.

Wow you a connected into some fun/scary circles to hear about that on the grapevine!

I don't see anything as exciting as that. Though I regularly see massive overdesign of member and very poor design and connection detailing in steel all the time. I have an eye for it as it is my bread and butter. Often it is subtleties, like having the wrong connection and having the wrong member being the continuous member like I saw on the new build on the weekend. Or a massively overly designed hollow section truss with thin end plate connecting segments where you can visibly see the gap that had opened up in the tension chord.

Or even the airport the other day where I can see daylight top through most of the moment joints. Probably insufficient bolt tension or possibly even plastic bolt stretch during extreme wind events leading to a rigid connection becoming a semi-rigid connection. A little scary given this is a major international airport.


I also regularly see horrible construction on many of the brownfield construction sites I visit. I hesitate to say engineering because you often never know if an engineer was ever involved or not. Mostly it is ancillary stuff, sometimes you even wonder how it is still standing!

 

[BAretired]

If they were "huge 3/4" gussets", I expect the tolerance could easily be plus or minus one inch, but to say there are no tolerances is hardly "the dumbest thing an engineer ever did". And I am pretty sure the same engineer, if inspecting the work, found a one inch deviation from the specified measurement would agree that it was okay.

He may not be so agreeable if he found a few missing nails. No tolerance with number of nails.

 

[bumbler]

I have two great ones:
My project manager (engineer with ~15 years experience) for a PT parking garage told me that increasing or decreasing the number of tendons in a post-tensioned beam will not affect deflection.
During shop drawing review for deferred balconies, I asked to show consideration of wind uplift. The engineer (~30 years experience) told me that he didn't need to design for wind uplift because live load will counteract it. Not only was he ignoring basic load combinations but the idea that people would have a party on a balcony during a design level wind event is one of the stupidest things I've heard in years from anyone.

 

[robyengIT]

I am Italian : "construction tolerances have been invented by ancient Romans". The dumbest thing I did : attached translation from spanish (Argentina)