Design "By Inspection"

[vmirat]

Sometimes, we engineers do design "by inspection". If something looks obvious, then we skip the calcs and just say "by inspection". Wind versus seismic is an example. But how far do you take this and how legal is it? It seems to be a judgement call on the part of the EOR, who is ultimately liable for what they design anyway. Are we just being lazy, saving money (time is money), or so arrogant to think that it is beneath us to have to do the calcs because of our vaste expanse of knowledge and experience? I've run into that last one from other engineers whose work I have had to review.

I'm guilty of doing it too, but always felt uncomfortable about it.

 

[Ron]

vmirat....it is common for the obvious items. Is it legal? Depends on the jurisdiction, but in my area the answer is "Yes"...it comes under engineering judgment. Engineers, unless required specifically by some authority having jurisdiction, do not have to submit or even do calculations. The risk they take in not doing calcs or other checking is their own. They do; however, need to meet the standard of care for their practice and area so that they are not accused of being negligent.

 

[msquared48]

Personally, with the probability of very little experience in the area "by inspecting" refers to, I would question the use of the term by an EIT. However, for a seasoned and licensed engineer with many years of experience, I am OK with it. Done it many times.

What constitutes "many years"? That, too, is a judgment call.

Mike McCann
MMC Engineering

 

[nutte]

As long as it is indeed "OK," I can't imagine it being "illegal." If someone were to run the calculatios and show that it's not OK, then you've messed up, and there would be a problem. But if one were to run the calculations and it still works, what harm has been done? An engineer's seal states that the design is adequate. How you got there (running calculations for that specific instance, or relying on experience to know it's OK based on a quick glance) is irrelevant, as long as the design is indeed adequate.

 

[msquared48]

That being said, many jusisdictions are from Missouri and say "show me", so the calcs still have to be done.

Mike McCann
MMC Engineering

 

[JStephen]

Part of being an experienced engineer is knowing what calculations need to be done in the first place. That involves experience with the topic at hand, and also depends on the resources at hand, the importance of the design, and the degree of conservatism built into the design. Put a steel beam across two bricks and you can analyze it in 5 minutes. Give the same problem to NASA and they could spend the next hundred years analyzing that situation. Or to put it another way, anything that can be engineered can be engineered to a greater or lesser extent, and part of the design job is to determine that extent.

 

[woodman88]

I find that whether I state it or not, that 80% of any major project is a "by inspection" calculation. Beams are a prime example. I hopefully catch the critical span/load for my first so I can state that the others are okay "by inspection". I do this because I do not think as engineers that we must calculate every beam for it's loading condition on a job. I have stated this to plan checkers who requested this and also stated I would go to the Building Official on the issue that the beams were okay "by inspection" if they wanted me to.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[Ron]

Garth...agree. I've had significant aluminum structures, subject to identical member loads, where the member sizes were the same but the spans were different. I only did the worst case with the remainder "by inspection" because of the obvious....yet when reviewed by either a non-engineer or worse, and idiot engineer, that was questioned. I consider that my prerogative of engineering judgment. I take the responsibility whether it is calculated or not.

 

[JedClampett]

Back in my nuclear engineering days, we called it "OK by judgment." We got challenged on it. It turns out that, duh, not everyone has the same judgment. So whoever didn't like our use (probably overuse) of "OK by judgment" asked us to document what we based our judgment on. So if we based it on that we designed a W8 x 18 that was longer and had similar loads we wrote that down "OK by comparison to beam 20" etc.

 

[TDIengineer]

Mike,
I got your Missouri joke!

Show me state!!! lol lol

 

[paddingtongreen]

I used to give my beams marks, say a run of similar beams would have the same number but any that had additional loads got an alpha subscript and were checked and the selection based on the worst in the run. I was also able to use this method on nuclear work.

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