Calculations: Personal Tool or Public Record 9

[JAE]

Here is a qustion for the ages.

Structural engineers provide professional services to their clients. These services involve taking specialized knowledge of material behaviors and applying them in such a way as to "turn ideas into reality."

The process in getting an idea put together that is strong enough, stiff enough, ductile enough, etc. and meets the required building codes involves the engineer using various tools. Traditionally, these tools have involved pencils, paper, calculators, slide rules, etc. Lately, computers and the internet have taken hold. All of these are simply tools that allow the engineer to apply his/her knowledge and create their true instrument of service - the design.

The way an engineer communicates this design is via drawings. The way the design is developed is via calculations. Calculations, I would suggest, are NOT the service an engineer provides. Calculations are NOT an entity that is sold to a client.

But today, it seems, calculations are required to be part of a "submittal" to cities, agencies, etc. as part of the compilation of services that need to be checked by a reviewer, usually an engineer-type working for the governing agency.

I would appreciate comments from you all out there as to your take on this. Are calculations something that should be "reviewed" or are they my own personal tool that allow me to organize my thoughts, develop my ideas, etc. Can a reviewer say, for example, that I need to format my calcs in a particular fashion? Are they stepping beyond their function to review plans for concurrance with a building code?

I guess my bottom line is that the calcs are a road map that show, perhaps, how I got from idea to design. But they (the calcs) are usually very much open to interpretation, confusion, etc. based on the way the engineer uses them to develop his ideas. Not everyone writes down or calculates things in the same way.

Thoughts on this?

 

[NanoMan]

When we purchase structural designs we always mandate calculations be included. The reasons include:

1) 10 years from now, we can back up the design with the calc's, even if the designer has moved, retired, or been hit by a bus.

2) If we're considering a change, we can check ourselves to see if it seems to be reasonable. If it's OK or borderline, then we can go back to the engineer for an update. If we're way off, then we know that we need to reassess the situation.

3) I like to do spot checking. It's not that I don't have confidence in the designer (or I wouldn't hire them to begin with) but my personality is such that I sleep better if I understand the "whys and wherefores". To quote Ronnie Ray-Gun, "Trust but verify."

4) If we're looking at a similar project, we can use the existing design calculations for estimating purposes on the new job. Otherwise, I've seen people try to apply linear scaling to a decidely non-linear case.

5) To me, it's just good practice. If I'm the customer, and I include it in my scope, then it shouldn't be a problem.

 

[JAE]

Taro: I'm amazed that you destroyed the calcs after the job - but that practice is consistent with the concept that the engineer provides a service, not labor, not calcs, not even technically the drawings, but a service of skill, art, science and judgement (per Ron). The calcs are a tool to get there, the drawings are a tool to communicate it. The OBJECT that someone gets from hiring an engineer is essentially the engineer's ABILITY to facilitate turning an idea into reality.

flame: I cannot agree with you that "the world" somehow owns my calculations....at least not in a free capitalistic society.

NanoMan: Your first sentence gives away exactly the underlying point I'm making. You say "When we purchase structural designs...". A client does not really purchase a structural design, like going into a store and picking out a shirt. They rather buy a service...a practice of an engineer in allowing the client to realize their dreams of a bridge or building. They are hiring the engineer to facilitate this process....they are not hiring labor, calculations, drawings, etc...

Also, 10 years from now, or 100 years from now, you do not NEED the original calculations if you have the original drawings to check a structure. In fact, I would argue that its better not to have the original calculations as you'd get a more objective check.

In reading the posts above, I feel that I've quite gone over the edge and ranted quite enough. I really appreciate the friendly debate and discussion - this started from a recent experience of mine and I thought I'd vent a bit...but all the posts above have added a lot to the whole issue - I just fear we engineers are creeping away from our professional roots and slowly becoming a commodity.

 

[Focht3]

[blue]JAE[/blue]:

Rant away! I agree with your position wholeheartedly. Guess I'll be fighting against submissions in the future...

(I don't get asked for mine - guess the agencies don't know what to do with us 'dirt guys'!)



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora.

 

[Taro]

JAE,

Destroying the calculations was mostly a liability issue. Say your calculations indicate that #4 bars at 8" were required in a slab. But for economic reasons you change your mind and provide #5 bars at 12" but don't go back and change the calcs. The strength is the same either way but non-technical people in the legal system aren't going to understand that. Their opinions can be easily swayed by lawyers to arrive at the conclusion that there is something wrong with the design. That's a simplistic example, but you get the point. As you pointed out, calcs are very much subject to interpretation.

The company's position was that if the design as shown on the drawings is code-compliant, then it doesn't matter what the calculations say. Structures don't get built according to calculations, they get built according to drawings.

 

[JAE]

Taro - is this something you still currently do?

 

[Taro]

No, my current company's policy is to archive the calcs at project closeout. Personally, I prefer to keep the calcs because it can make life easier when you get called back to make alterations to a structure in the future. But for risk management, my previous company's policy also makes sense.

 

[sc]

So if you destroy the calcs and the job fails (thankfully very rare), how do you prove that you did not make an error?

All of the firms that I have worked at have kept calcs and sketches (and just about every other scrap of paper related to the job) as a record of the design process. Now that most firms are using software to a larger extent, I would think that backup CD's etc are kept of all design documents.

How does it sound in court, "no your honour, we destroyed the calculations as they are not part of the service provided".

As for the excuse given that lawyers can twist what is written, it doesn't wash as a reasonable engineer will either document the change by a file note or be able to adequately explain that the change makes no difference to the design apart from sizes and numbers.

Structures do get built according to calculations as drawings are drawn to represent the results of the calculations.

My rant
sc

 

[egc]

An issue I did not see raised is when peer review is required. This specifically (usually) requires submittal of the drawings and the calculations. In Florida, there are several municipalities/counties that are now requiring calculations to be submitted on even single family residences. In most cases these calculations are minimal (design criteria, worst case wall/foundation/beam designs, etc).

I just hang here (occasionally)

 

[denoid]

Good topic, everyone!

Here's a few of my miscellaneous ramblings (for whatever they're worth).

In my younger days, I once worked with another structural engineer in Chicago who did all of his calculations AFTER he finished the drawings. He'd punch the numbers and figure the sizes, and throw them on the drawings, but he wouldn't put pencil to paper on the calc sheet until he was all done. Can't say I would always agree with the method, but it was to guard against discrepancies in design vs. what showed up on the drawings that Taro alluded to.

Finally, several years ago, I had to do a foundation design for an aerospace project in So. California (I reside in the Midwest) where the calculations had to be submitted to the local plan reviewer. A few weeks later, I got a call from the reviewer who said he didn't understand my design. As much as I tried to explain over the phone, he insisted on a face-to-face meeting to discuss my calculations. I had the reviewer call my client to let him know that the permit would not be issued without this meeting. Reluctantly, the Owner agreed to fly me out there for the meeting (additional cost to them for plane tickets, hotels, meals, and my added time). Fortunately, the Architect and an Owner's representative accompanied me, because the meeting was almost comical. It lasted about 20 minutes, and involved the reviewer (a young, inexperienced engineer) asking me about 5 or 6 questions, which were easily explained, and already documented (he just really hadn't looked at the calculations). He gave my client and the Owner the permit that afternoon.

Had it been my money, I would have been PO'ed too. I got a free trip to sunny California in January, but I've always resented the nonsense involved in the calculation submittal process, too.

When, as an SER, I ask for calcs from vendors, I usually just check for the design criteria, and spot check the method. When I have to submit my calcs to someone else, I expect the same level of scrutiny, especially if they don't really know what they're looking at.

 

[Taro]

sc,
If there is a lawsuit you can always go back and recreate calculations that prove the adequacy of the design. In fact, you might want to do that even if you still had the calcs to sharpen your pencil and eliminate some of the "guesstimates" that are always a part of design.

The VP and CFO of the company was also the president of the American Society of Civil Engineers Structural Engineering Institute (SEI). He knows his stuff when it comes to risk management, so I believe him when he says there is less potential liability with destroying the calcs.

 

[RASmithPE]

I agree w/JAE, here's why.

When performing a peer review, I check and coordinate the plans, never the calcs. As soon as one looks at the calcs they can't help being "sucked into" the same design philosophies and assumptions. The review is no longer independent.

Structures usually fail because of gross mistakes in the basic assumptions or the connections. An experienced engineer needs to spot mistakes by studying the plans, not by checking arithmetic.

Any check can only be performed by locating the questionable areas and performing a truly independent check. I find it about as fast to recalculate as to read another’s calc's anyway. I will, on occasion, ask for FEA inputs for more complex structures to save me modeling time.

I avoid submitting calc's for this reason as well as all those previously mentioned. I enjoy an independent check of my work but if someone questions a beam on my plan, let him or her send me his or her check calc. Comments?

 

[RiBeneke]

JAE
A most interesting topic. I agree with your views.
Here in South Africa the calcs are seldom asked for or reviewed by the building control authorities. However peer review (inside or outside one's organisation is not uncommon).
I agree with RASmith that if calcs are submitted for review, then the arithmetic is not the main thing to be checked. If the checker is competent then they should be able to do the arithmetic themselves using their own tools like software and tables and spreadsheets. In some cases these tools are proprietary items that I would consider my professional briefcase.
I believe that if 'design information' is to be submitted for review, then the important items are the INPUT such as
load cases, geotechnical and environmental parameters, applied loads, service and dimensional requirements, material properties, analysis assumptions etc
and the OUTPUT such as calculated deflections, stability factors, dynamic response, safety factors etc and of course drawings and project specifications. A competent checking engineer should assess the correctness of the INPUT and then use their own methods to confirm the OUTPUT. Just checking someone else's arithmetic is no way to check a design.

 

[Lutfi]

Give me any drawings and design criteria and I will check any design. I really do not need calculations to check the design.

To make things more complex, in one recent situation where I was doing a peer review, I asked the engineer for his calculations. I was provided with over 100 pages of STAAD Pro dumb that 90% of it was useless. All I needed is the input model. The scary part was that was the first time the engineer ever used STAAD! He had seven load cases; he ran the model seven times in lieu of creating basic load cases and load combinations in one model. His method was not wrong; however, it was frustrating to me and it was very inefficient procedure.

I agree with two arguments made above. The first is checking others’ calculations will suck you in to their approach and the second I firmly believe that I can do any calculations if I have the drawings and the design criteria. Sometimes in absence or presence of drawings I still do field investigations and measurements. I do not have time to tell the horror stories that I discover while doing field investigations. Changes that are done, during construction, that go by unnoticed by owners and sometimes engineers.

Now I step of my soapbox.

 

[haynewp]

I have started doing calcs later in the projects, after the drawings are almost completely done. For the buildings I usually deal with, I can get pretty close to final member sizes by quick hand check or estimates by experience. Since the drawings are always in immediate demand, I stay ahead or with the architects this way and I don't have to spend hours going back later in the project to change calcs because the architects raised the roof 5 feet etc.

With almost everyone doing some form of computerized calcs now, what Lutfi mentioned makes me wonder what are the reviewers accomplishing if the programs are inaccurate? If my calcs are going to be scrutinized, and for instance I did my model in RAM or some other program where there is not a full explanation of how the program got from input to answer, shouldn't the program code also be getting scrutinized for accuracy?

I feel if I am taking responsiblity by signing the drawings, I shouldn't have to prove how I reached my drawing data to anyone. However at the same time, I always feel better when someone looks over my design, calcs included.

 

[cap4000]

I agree with you sc that calculations should be kept and made available for the reviewing agencies, architects, or owners. However, Design Failures are not as rare as you think as many books have been written on the subject. As litigation is soaring today I strongly recommend every engineer retain copies of most of the calc's. I still have some of my calc's from 25 years ago . Taro,your right about liability issues. IF a job goes bad,lawyers immediately issue a subpoena for the calc's. Having them, means less potential liabilty and a clear recollection of the facts even years later. Having none,looks like you may be hiding something. Nice Thread.

 

[BigH]

The problem with design calcs is that people don't do things always the same way - at least in geotechnical engineering. There are the "formulas" but the tests and subsequent judgments that put the values into the formulas may differ (hopefully only slightly) from experienced geotech to another. Say, I wish to use 15kPa for Su - and Focht3 decides to use 17kPa. Who is right? Hard to say - is the need to satisfy a ticked box, or is someone going to go through and nit on each and every point of judgment? In settlement calculations, I might use preconsolidation pressure of 50kPa; VAD might suggest 70kPa; others slightly different. As a result, we will all get slightly different answers. (hope Focht3 and VAD don't mind my using their handles!).

So, calculations and the need for them - differs perhaps from structural engineers to geotechs or irrigation engineers. Do you give them to the client - if he has a legal right to them, i.e., it is a contractual obligation, then yes, you must give them to him. If not, no. I would always welcome an honest peer review, though, with a chance to defend my numbers, so to speak.

 

[Focht3]

No problem, [blue]BigH[/blue]. And very relevant to this discussion; I don't think most structural engineers understand how much of geotechnical engineering design has to do with personal choices, and very few codes. (This is true in much of the U.S. but is not true world wide.)

I dealt with that very issue in 1990/1991 while working in southern California. My employer was selected to do the geotechnical design for a large interchange of one of the proposed Orange County toll roads. It was principally my project. What a headache! The bureaucrats in charge had no idea what to expect from the local ground conditions, or even what many of the important design/construction issues were. (They did 'get it' on the earthquake issue.) All they wanted to do was limit the costs.

And they nitpicked our calculations - insisted on justification of every design approach. It was far worse than grad school - at least I could expect that my professors understood the principal design approaches for embankments and bridges.

I can see why some would destroy their calculations in order to avoid that experience in a lawsuit -



Please see FAQ731-376 for great suggestions on how to make the best use of Eng-Tips Fora. See faq158-922 for recommendations regarding the question, "How Do You Evaluate Fill Settlement Beneath Structures?"

 

[flamby]

How much chance a doctor has to run his practice if his known method is to cure the patient by some mysterious drugs and burning the prescriptions after curing the patient? How much chance an engineer has to run his practice in a free capitalistic society if he doesn't prove his design to be safe and economical? And how do you prove it apart from showing it by calculations? Calculations are tools, fine, but they are also the /justification/ of the design. If you have a high repute, probably you can get away without showing the design already gone to your dustbin. But this be treated as exception rather than the rule. Either you get unquestionable reputation or get ready to be asked for calculations.

JAE can keep his calculations to himself while flame can not.

 

[JAE]

flame - I agree that calcs are also the justification for the design, no question. But your doctor analogy doesn't work.

A doctor isn't asked for his step-by-step process of diagnosis and treatment. Yes, the drugs he uses are tested but so are my welds, concrete, steel, bolts, etc. But his PRACTICE of medicine is not reviewed each and every time by another doctor. Only when there are problems does a review board get involved. And then, the review board is populated by other qualified doctors, not government bureacrats. The patient doesn't ask for the doctors justification for all his steps in healing.

I can just see a patient saying, "Well that's great, doc, that you want me to stop eating bacon, go through a procedure to clear up my veins, and then do a bypass surgery on my heart, but before all that, doc, I need to see all your logic and diagnosis procedure written down and cross referenced to medical journals and texts before I'll believe you have correctly suggested the right thing for me." We don't do that because the state has LICENSED the guy and verified that he knows what he's doing. The patient is paying for the healing service - not the process of getting there...that's the domain of the doctor himself.

Likewise, we engineers are LICENSED to practice. We are identified as having the proper education and experience and are qualified to perform engineering services....

So when we submit plans for permits, a governing body should not HAVE to see our calcs. It is unecessary. It is stupid because the reviewers many times don't understand what they are reviewing anyway.

flame, you really hit the point - "if you have a high repute, probably you can get away without showing your dseign...", By submitting calcs to a government lacky, we have really lost our engineering "repute".

 

[connect2]

We never submit design calculations with our building permit drawings, permit drawings being a legal document. however there are a number of requirements on the drawings with regards to stated info. such as design loads, design standards used, details, dimensions etc., etc., There should alsways be sufficient detail so that a third party can check your design and query you if required. Here if another Prof. Engineer is asked to review your work then he is required to contact you before review.

Only a Prof. Engineer is competent to review our work. If we are asked by another P.Eng about our work we require him to submit his question to us in writing and as 'Engineers of Record' we will consider the query. We also inform them, in writing, that they are now a full participant in the future liability with us of the total project and that we consider this to be fair, amazingly enough I would say more than 3/4 of them never respond after this. We also inform them that they are bound to deal with us directly and never through our client. This is a 'Professionalism' issue.

We are fortunate to never have been involved in Public (Government) works. I learned from an 'older' engineer never to get involved with 'pissing' matches with other structural engineers. We are fortunate to always have been to busy and therefore always have turned down the request to review another structural engineers work.

Forensic Engineering we do a fair bit of it. When we find a problem we always work it out with the 'Engineer of Record' before the client or public ever gets knowledge of what happened. We never get involved in strength type failures, only serviceability type failures. We have been involved in one Disiplinary Hearing, not as the defendant, brought forward by a Chief Building Official, and it turned my stomach.

You want our calculations you'd better be ready to fight if you can't figure it out yourself. There is an 'artistic' side to structural, thank-god, and it's knowledge built up over a long time.

I'm knocking on wood all over the place right now!!!!