How often do your calculations get checked ? 12

[trainguy]

Hi all.

In my 13 years as a structural engineer (8 in buildings & 5 in railcar structures), I can count on one hand the number of times my design calcs. have been checked by a second engineer. I've always worked in small engineering firms that simply didn't have the time or budget for it.

Usually, design drawings have been reviewed for blatant omissions etc, but nothing more.

I'm curious how many of you other engineers out there are in the same boat. Any thoughts?

 

[trainguy]

Thanks for the interesting responses, everyone.

Thanks also for giving me a perpetually nervous stomach...

Joking.

GA

 

[samdamon]

My two cents-

Checking of calcs has varied tremendously depending on where I worked. My first job out of college was in the structural dept of a large paper company that did all its structural work in-house. Many of the engineers at this company had been there a long time, and they were careful and detail oriented. Plans did not go out until they had been carefully reviewed by the structural department head or a project manager. Sometimes the calcs were reviewed also, sometimes not.

Subsequently I worked for several different size consultants, one an A/E, the other an E. No one ever checked my work at these places, besides an occasional, cursory review at the end of the project just before the drawings went out. The resulting comments usually had more to do with what types of practices and details the reviewer preferred, rather than corrections to gross mistakes or problems.

At the A/E, a mechanical engineer sometimes sealed the structural drawings. So much for quality control (not to say the laws governing our profession!).

 

[PM]

I've worked for the fifth largest engineering firm in the world, and for the smallest firm in the world (ie. my own) and my structural design calculations have been reviewed exactly 5 times so far (ie. 3 times in 1976 and twice in 1977). I've designed multi-million dollar wharves, bridges, dams and buildings. I have never yet been involved with a claim related to a design error or omission. I'd like to think I'm smart, but the truth is I'm lucky.

The only procedure I've found that is both cost efficient and effective at finding significant errors is to have one of my expert colleagues review the drawings and specs. Most bridges, wharves and building structures can be visually scanned in an afternoon. With a little experiece and lots of concentration, it's amasing how quickly blunders jump off the page. When I think of the major structural collapses in recent years, none of them should have escaped a visual ispection of drawings by an expert.

I liked Ginger's comments, but the following point may not be as absolute as presented. "The common law of business balance prohibits paying a little and getting a lot.
It can't be done."I think it can be done.

A few years back I was reviewing construction bids for a concrete caisson wharf extension. The low bid was less than half the next higher bid and almost 33% of the average of the other bids. One would think this was an error, but it turns out the bidder had a set of slip forms from a recent previous job and could produce the few required cribs at half the cost of other equally qualified constructors. The owner almost dismissed the low bid on the basis of "fundamental error", but ended up accepting and ultimately was happy with the outcome. Just goes to show anything is possible.

Regards,

 

[bridgebuster]

Forgive me, but I need to add another two-cents worth about the value of checking calculations:

Last winter I was asked to seal a set of "revised" bridge plans. First, I need to explain my use of "revised". I was the project engineer for the original design that was completed about one year earlier. After that, I was on a field assignment during which time there were substantial changes in the highway alignment requiring redesign of the bridges; they became longer. [The redesign was left pretty much to a group of junior engineers; then again whatever guidance they received from senior engineers was worthless]. When the time came to submit the drawings, lo and behold, I was directed by the management to seal the plans [I was one of only two people licensed in that state.] I refused to do so because the work was not done under my supervision.

After much wailing and gnashing of teeth, the project manager finally agreed to speak with the state board about my concerns. The Board's descision was that I could seal the plans provided that I personally check the calculations and plans. With that resolved I agreed to seal the plans. Initially the PM refused to give me the calculations because "it's to much work to send you a copy". His position as well as that of our branch manager was that if the plans are checked that's good enough. Obviously, they didn't understand that if the calculations are wrong, the drawings are wrong.

Well, back to square one. Finally, they agred to give me the calculatons. In the meantime, they asked me to look at the drawings, which were an abomination! Things just didn't look right.

When I got to the calculations, my fears were realized: Not one page was ever checked. Everything was wrong; among other things:The abutments were underdesigned. The bearing design was wrong. The reactions shown on the plans did not match the ones from the computer output. Actually, there was no design for the bearings someone just put the old calculations in the book. The girder splice design was wrong. [Someone needlessly added wind bracing on the plans and decided to shift the splice location 10' but never redesigned the splice. The wind bracing was unnecessary and the way it was detailed, it wouldn't do any good anyway. This should be no surprise - there weren't any calculations for the bracing.] The girders were significantly overdesigned.

Bottom line: The office had to eat the cost of four people to start from scratch; it took about five months. Luckily, there was a partial delay by the client due to funding issues and management was able to stall for more time. Meanwhile, we looked pretty foolish issue substitution sheets during the bidding process.

 

[Qshake]

Bridgebuster I offer my apologies that our profession, which we (perhaps naively) beleive to stand on high moral and ethical ground could have ever allowed such a travesty.

However, I am glad to know how you handled the situation and beleive that you acted in everyway as I would had I been in such a position. You are a good engineer and if they would have postured by hanging your paycheck over your head, you could have easily found employment elsewhere. Best of all, you showed the junior engineers that work itself is not good work or work worthy of being sealed and that drawings by virtue of having ink on the sheets are not worthy of construction. You showed them that arrogance (consultant is right, client is wrong - what does the client know anyway) has no place in our profession and that when principles are on the line those engineers have a place to turn to as well.

Thanks!

 

[bridgebuster]

Thanks Qshake

 

[Evank]

Many excellent comments. Mine may be of interest. I graduated from Univ of Colorado in 1938. No graduate got a job. Desolation!! Finally I received an offer from the American Bridge Company in Trenton, NJ. As a detailer absolutely eveything was thoroughly checked and counter checked. They could not afford to have holes mismatched.
Since I was born with one eye the armed forces would have nothing to do with me, so I found a job in structural analysis in the aircraft industry. I worked throught the war on at least some part of practically everything that flew, since we subcontrcted large sections. Everything was checked.
After that I worked with a small structural consultant, designing relatively large projects. Nothing was checked.

I later opened my own office. Then I went with a large international A/E.Then I went to another large A/E. Then I quit the race and opened my own office again.

So what has been my experience? Generally speaking, it depends. If the product produces an extremely refined product such as going to the moon, everything is checked again and again. If it is the joists under a frame office building then if the doer is at all experrienced, it is not checked. And if the design is based on data that is not precise, like an office live load, I do not feel worried about that so much as if it is based on the gravitational pull of Mars as it goes by.

So an engineer's judgement which is supposed to be professional, is very important.

Evank, Structural Engineer

 

[trilinga]

Evank
Salutations to one of the very senior members of the forum from a relatively younger generation.

As you have rightly stated at the end, an engineer's professional judgement is equivalent to a number of repeated checkings. But I prsonally feel that this professional judgement is the result of carrying out a number of such checking and counterchecking through one's career. I am sure you will agree with me that going through this experience during your early years of your career has given you that professional confidence.

Right or wrong, the present day younger generation is not having such an opportunity. The exposure to a variety of 'black box' type computer software has made many of them less alert in terms of checking. There seems to be a tendency of 'taking for granted' the results from a software. the attainment of Professional judging capability is retarded by the lack of manual working and understanding the basis of analysis and design. Many of them are very good at operating the software but they know neither to justify their results nor to doubt them. If they get an undesirable result, they do not know which parameter to change to correct it. In short, the 'Physical feel' of the calculations is missing.

There may be a few exceptions to the above but I feel the majority fit into this pattern.

I would suggest that it is best to have a person of your caliber and experience at the exit point to see everything is OK but still have the systematic checking procedure which not only ensures the quality but also make the people down the ladder to become like you in the coming years.

 

[Qshake]

Evank, I second your thoughts/experiences and would like to add that (and maybe I'm speaking out of turn here) nearly every shop fabricator that I have worked with (mainly medium to large companies) have outstanding records with respect to shop drawings. It has been my experience (unfortunately) that when the shop calls it usually amounts to an oversight on the engineers part. While I'm not proud of that I wanted to point out the meticulous job done by the fabricator, who as you've stated can ill afford to have holes misaligned. However, mistakes do happen and usually when a field engineer calls a mistake has been made in fabrication. Now this doesn't happen often but in the case of working with existing facilities it does happen and usually because the contractor didn't take the appropriate field dimensions.

 

[mobe]

I think trilinga has made a major point regarding the use of computer software by younger engineers. Many now use programmes for working out very basic stuff that us older guys just turn out using "hand calculations"
In many companies senior engineers have also been guilty of dumping the number crunching aspect onto graduates who are more adept at everyday computer skills but have little feel for the overall design of the whole or the elements. It's easy to hit a default button and end up with an E value for steel when it should have been for aluminium. There is also still the problem that commercial organisations produce charts listing stresses, deflections etc with no supporting background as to the derivation of these, all of course produced by some magic software that is beyond reproach.Ever tried phoning some of these companies and asking just how these results were produced?
Fair do's, computer software has revolutionised everything but as far as checking what is produced, we still need to keep the maxim "rubbish in, rubbish out" uppermost in our minds when overviewing a design.
All design needs to be checked; no matter how long one has been doing the job a fresh look can often see the wood from the trees - something that is overlooked if working in isolation.

 

[DaveVikingPE]

Wow, Evank! You didn't happen to run into L. Sprague De Camp (RIP) - a young, unemployed engineer at the time - in your travels circa 1938?

To the subject, My cacluations usually are a mix of hand calcs, printouts from computer programs (with a lot of hand notations on them; I usually hand-compute the first iteration of a design calc, then verify it on the computer, then crank out however many variations with the computer as I judge necessary) and photocopies of whatever pages from whatever documents (e.g., company literature or textbook tables, etc.). All the pages are numbered and I include a table of contents at the beginning, so it's easy to follow... Where I work "checking" isn't what's done, an "Independent Technical Review" is conducted once I'm finished and that's there where actual checking is done. Do I like that? Eh, maybe, maybe not. But to answer the thread, my calcs are checked 100% of the time.

A design calc package I hand in for review starts off with a one-page narrative/memo then a series of "draft final" sketches - usually CAD work (I do it, we have no draftspersons) that doesn't include borders, logos, etc. I assume that the person doing the review will immediately spot errors and/or omisions just by looking at the sketches (hopefully I haven't made any) - we usually have extremely senior design engineers doing the reviews, an awesome benefit.

 

[Evank]

From EvanK
We have had some extremely wise comments. They all have merit and none give a black or white answer!!
The comment about the blind use of the computer is one we should keep in mind. There was a failure of a gymnasium roof in Connecticut about 30 years ago. It was a dommed long span that had been designed by the then new computer thing. It failed early in the morning after a snow storm. It was discovered that the conmputer had faithfully designed it just fine, but had not included the effect of one sided snow load. And the snow had accumulated behind a parapet and not the other.
But I admit I am looking at this from a different perspective than others. I still depend on the judgement of designers if they have had sufficient experience to merit trust. So I guess it is TRUST that I look for, and not the nuts and bolts of checking arithmatic or the printouts from a computer, wonderful as they are.
Thanks for your comments. It has been very informative.

 

[Evank]

DaveViking
No, I do not recall Sprague... in those years. Most of us were unemployed, and I worked for a month or so at the Federal Land Bank in Wichita. An exciting job of drafting onto maps the locations of Land Grants. I could not stand that pressure so went to American Bridge in Trenton. No better place, but WW II changed all that.
EvanK
Structural Engineer

 

[Ron]

OK...this is a long thread, but I'll make it longer!

Individual competence and diligence are necessities in engineering. As some have said thus far, our younger engineers don't always have the opportunity to learn the importance of these necessities. In the interest of expedience, we often allow younger engineers to "sink or swim". This is not an appropriate posture. Engineering is not a "Risk Management" proposition. It is a scientific methodology. The "Risk Management" approach causes the problem bridgebuster described (which he handled nicely and correctly in my opinion). We have to continue to apply a scientific methodology even in the face of inaccuracies (structural loads, assumptions, etc.) and absurdities (management philosophy), simply because we compound our errors when we don't.

I'm a great proponent of progress and computerization, but I still check my calculations (after a cooling period!) and those of the engineers I mentor. I also welcome the check by others...even though I have a lot of experience, I'm not infallible. Those of us who remember slide rules also remember the need for "order of magnitude" checking. This mental process is necessary and good. I try to instill it in those I mentor, even though we obviously don't use the slide rule. I do this through sometimes subtle (sometimes not so subtle) questioning of their approach and how they came to realize their analysis or design. I have soiled the back of many a napkin in this process!

 

[DanTex]

Hmmmm.... Sign off on an unchecked design??? Make a semi-major mistake and you probably won't like the time you spend in front of a judge very much.

You design it and sign off on the plans and someone dies. There's no question about it... it's your fault ( 100% ). Not checking can easily be considered as negligent or incompetent.

I work for a large government agency doing bridge designs. We also review bridge design plans developed by private firms. It is very obvious to us here that a LOT of private firms don't do very good checking on their designs even though their contract states that they are supposed to do all designing and checking ( they are paid quite well for their services... I see no excuse for them shortchanging the process ). The number of blatant erros we find in their plans is awful.

Dan

http://www.dtware.com

 

[Qshake]

Dan,

I used to work for a large government agency doing the same thing many, many years ago. I've worked in consulting for a longer time now as well. But one thing that gripes me is exactly what you stated in you last post. Errors are far too common and the industry seems to be very complacent about it. Others, including the company I work for have developed Quality procedures that are meant to curb this but in my opinion they are sometimes too cumbersome and extravagant to do any good. I have always relied on the two sets of eyes check on everything before it goes out - and that includes preliminary drawings.

Another things that gripes me is the way some companies don't produce plans like those provided by the government agency - doing so has many benefits not the least is easier review and coordination with other plan sets and contractor familiarity. Inevitably, I see someone who wants to re-invent the wheel just to be different, just to stand out. It drives me crazy!

 

[BantrelStructural]

I currently work for a major EPC consultant in the oil & gas industry. We are ISO 9001 registered, and have committed to checking all calcs. This is actually too much. Some stuff needs checking, maybe even more than once, other items could probably go with no checks.

In my earlier commercial consulting days little was formally checked, but I used to do my own reality checks. Manual load take downs were checked (reactions totalled, applied loads totalled - were they reasonably matched?). Larger more critical members, I would recheck, with a different method if I could.

As someone earlier mentioned even senior engineers can make silly little mistakes, and as one of my profs used to say (his Law 199) no one mistake usually causes a collapse, it takes an accumulation of mistakes. An early boss tought me a simple rule - does it look right? Many mistakes can be spotted by looking at something with a detached eye, and the absurdity can jump right out at you. Experienced designers (technicians) and draughtsmen can often spot these goofs.

In the calc checking that we currently have to do we have two options. Literal detail calculation checks, or alternate approach. I generally hate the detail calc check, particularly with some individuals whose calcs while maybe correct are extremely difficult to follow, so I tend to favour trying to come at a problem from a different angle and see if I arrive at a similar solution whenever I can.

On one project with an intermediate engineer whose calculations were always difficult to follow, I was getting quite frustrated trying to follow/check his numbers, so I decided to sit back and look at the problem a little differently, and the flaw that I finally found in his calculations was not in the number crunching itself, but in an assumption of flange continuity that I was not convinced was realistic (vessel lifting beams were cantilevered off eiher side of a deeper saddle extension, so that the top, compression flange was discontinuous, with only a partially stiffened web plate connecting them). In lieu of doing a detailed finite element analysis to make sure that we would not get local plate buckling somewhere in the beam/saddle combination causing us to drop the 150 ton vessel/platform assembly during the critical installation lift, I decided to add some temporary lift bracing between the upper and lower top flanges to transmit these forces via truss action. Although the other end was more lightly loaded and did not present a "failure" problem in the number crunching, higher than anticipated deflection during a lift to weigh the module caused us to decide to add the flange braces at that end too. This was partially exacerbated by the fact that the vendor had given us a bad c-of-g and so we actually had more load on the other support than we had expected. But basically the check here had been sit back and look at the overall concept, not get tangled up in all the detailed numbers.

 

[chimney]

Error is human.Checking of calculation is necessary if there is need to submit the calculations along with drawings.Now a days due to competition everybody has to quote less in order to remain in bussiness .Hence provision for double check is usally avioded. Whole world is behind quality but nobody is following it to its core.With experience seeing the drawing itself one can judge the adequacy of the strutural members.According to me checking of calculation is essential only if it needs the reveiw of the client/other agency.But the drawings are to be checked perfectly.