Skeletons in the closet? 4

[greznik91]

Hi
I have to ask - do you guys have any skeletons in the closet? Have you ever designed something that was built / is going to be build but it wasnt designed as it should be - you have realized there are some errors or incorrect modeling or assumptions in your calculations that you have figured later (while working on another similar projects), what have you done about it? How often do you think about it? Ever nervous of consequences? I know there are safety factors and all that but still... This topic may not be popular but I think its a part of our job and would like to hear some thoughts.

 

[kissymoose]

Hard question to answer, why don't you go first? Lead by example.

 

[CANPRO]

Can't say I have any "skeletons", but I've come across some of my design drawings from years past that have made me cringe a little bit, but nothing concerning on a safety level. I've also made mistakes that weren't safety critical, but still sucked - designs that weren't construct-able...only injury there was my own pride after getting chewed out by the boss.

 

[Ron247]

I doubt I would ever answer this in an open forum. Nothing to gain, everything to lose. "Forgive me Father, because if I looked hard enough, I can probably find that I have sinned."

 

[JAE]

There have been many times when I've finished a particular design, only to be "prompted" or nudged somehow, or simply I just "noticed" my design and thought, "that can't be right".
Only to find that indeed, I had made some error and I then corrected my design.

For we structural engineers, the errors in member sizing can sometimes be forgiven - or even survive the test of time.
It's the connection designs that wreak havoc, collapse, and disaster most of the time.

I recall Edward Pfhrang who once spoke at an event outlining the Kansas City Hyatt Regency collapse and he stated, [blue]"We engineers need to stop thinking of our structures as members connected together at joints, but rather, our structures are connections linked together by members."[/blue]

In other words - pay very close attention to connections.

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[Rabbit12]

I can share a story.

A few years ago the company I was working for was designing a new addition to an existing structure. The same company had designed the original structure. We decided to connect to the existing structure and utilize some of the existing braced frames. During the course of the design I discovered some existing interior braced frame footings that were woefully under-designed for uplift. The structure had been in-service for several years with no apparent issues with performance.

When I dug into the existing design a computer program had been used to analyze the system seismically which automatically calculated the effective seismic weight. The effective seismic weight was 1/2 or so of what it should have been. I had always done a quick hand calc check for the effective seismic weight to make sure the program was calculating it correctly. When I discovered that error it reinforced that a quick hand calc is a good idea for certain things to verify structural modeling results.

We ended up going to the owner and explaining the situation. We designed and paid for installing helical piles to resist uplift.

I know both the designing and stamping engineer well. Both are incredibly smart and extremely talented engineers. Moral of the story, it can happen to anyone.

 

[JoshPlumSE]

I've had two things that don't "calc out".
1) Issue #1: I made a calculation error that wasn't found until after the thing was built. It was only had an "overstress" during hydrostatic test. But, they'd already don't the hydrotest and everything worked great. Thank goodness for safety factors.

2) Issue #2: They moved a wood post during construction. The post was supported by continuous wood beam. Originally the post fell directly over the support for the beam. When they moved it, it landed off the support by a few inches. So, it's a shear and compression perpendicular to grain. Big difference in capacity, right? Well it was close. Maybe a 12% overstress. Rather than making them tear it out, I decided to live with it. I was stressed about it for awhile.... Now, I'm glad I let it go, because just a couple of years later the NDS doubled all the allowable shear stress values.

 

[dauwerda]

The Citicorp Tower was the "ethical case study" presented to me while in college.

http://www.engineersjournal.ie/2015/12/08/citicorp-centre-tower-failure-averted/

 

[SlideRuleEra]

I had a project to redesign and replace the OEM designed track for a heavily loaded carriage used to pull loaded railcars through an unloader. Had reasonable values for the applied loads but I underestimate the ill-defined cyclical impact loading. Track lasted one year (the same length of time as the OEM design). On the follow-up project, I used much larger impact loading... which worked.

Lesson learned... give careful consideration any potential loading which is not well defined.

http://www.SlideRuleEra.net

 

[TLHS]

SRE: The good old "When in doubt, make it stout"

 

[SlideRuleEra]

TLHS - Great summary!

http://www.SlideRuleEra.net

 

[hokie66]

I now know that a number of one and two story structures which I designed in the 1960's, schools and commercial buildings, should have received a lot more attention to lateral loading. But as far as I know, none have failed.

 

[MIStructE_IRE]

If building’s actually fell down we’d be much richer men..

 

[jayrod12]

If building’s actually fell down we’d be much richer men..

At first, only half of us... then the problem would be self correcting.

 

[KootK]

At first, only half of us... then the problem would be self correcting.

As luck would have it, I know just the fellow to help us out with this.

 

[vmirat]

I have this on my wall...
"Engineering is the art of modelling materials we do not wholly understand, into shapes we cannot precisely analyse so as to withstand forces we cannot properly assess, in such a way that the public has no reason to suspect the extent of our ignorance."
I've seen various people given credit for it.

I have also looked back at some of my early designs with some cringing. I tend to be conservative in load calcs, so I'm not too concerned about failure. Responsible engineers will do the following:
1. Know your limitations. Don't take on a project that exceeds your expertise.
2. If you're not sure of something, seek out the advice of others. This can be hard if your self-employed, which is where Eng-Tips can be a great resource.
3. Don't use software unless you've done the same kind of calcs by hand a few times.
4. Keep detailed records. That mechanical engineer that told you the RTU only weighed 2,000 pounds, but actually weighed 5,000 pounds, is the one at fault, not you.
5. Have the professional integrity to admit you made a mistake. You might lose your job but lives could be at risk. I had to do this once. It was very uncomfortable, but it was the right thing to do. In the end, things turned out fine and the impact on me was minimal.

 

[kissymoose]

Let's get you to 1000 KootK, that was hilarious.

 

[TehMightyEngineer]

I used to keep a bungee cord around from a project that went south back in my EIT days, nothing scary but it's the only project I was ever involved with that wasn't successful. Decided it was time to throw the bungee cord out when I started my own company.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)

 

[Settingsun]

JAE, spot on about connections. In an early steel design course, the lecturer told us that contractors price steel tonnage then add 20% for the connections. Engineers on the other hand should spend 80% on connections.

In terms of skeletons, no one should know about a serious one. But no one knew the Hyatt Regency was barely standing up under self-weight. Real skeletons are invisible...

 

[dhengr]

TME:
Now that you are older and wiser, what do you use for bldg. x-bracing, instead of bungee cords? Or, were you using the bungee cords to hold precast products on truck trailers during transport? And, now that you have your own office, you finally have a legitimate need for some bungee cords, to hold the business together some days.