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Units, formulas, anyone?
4

Units, formulas, anyone?

Units, formulas, anyone?

(OP)
So... this turned out to be more of a rant than I expected... sorry.

I check a lot of submittals.  Most submittals are rebar shop drawings, concrete mix designs, that kind of thing.  Sometimes I get submittals for cold formed steel curtain walls designed by others and things like that, and they have calculations attached.  More often than not the calculations are very vague, employ some type of software printout that is completely foreign to me, and any hand calcs are not accompanied by formulas or units.  In my designs I have to do all of my calculations by hand.  Software can assist me in choosing the best shape, but I cannot turn that in for a design.  Maybe I'm jealous?

When I was in school (less than a year ago) there were some very basic principles that needed to be followed, such as: No units?  No credit.  If we were allowed to use something like the AISC Steel Manual and we used formulas from it, No reference?  No credit.  My professors always told me "if I can't look and see what you did it's useless.  People in the industry won't stand for incomplete calculations."

Getting to the point, I have reviewed so many calcs that have only solutions with no work, some work but no labels or units, or (my favorite) "[beam, column, footing, ect.] OK by inspection."  Is it wrong for me to see this phenomenon as any of several things: sloppy, lazy, unprofessional, and/or arrogant?  I think it's great that some people are so good at what they do they don't actually need to verify their design with numbers.  Wonderful.  In all honesty, I AM jealous, but I'm expected to approve this?  How can I possibly check and approve anything when there isn't actually anything worth something to look at?  Most often from my supervisors I get "I'm sure they know what they're doing, they've been working there forever, it looks OK."  OK, let's assume they have the competency to do that kind of thing, but are we to assume that they didn't make a mistake?  Isn't that what checking is all about?  How do you check off on "OK by inspection?"

Structural Review Comments:  Pretty pictures, straight lines, good handwriting.  Calcs?  Eh... ya sure, he/she is probably right.

I understand that some calcs are very basic but is it too much effort to write out a formula?  Use units?  Labels?  Give actual insight into design methodology?  Isn't this Engineering 101?

Is this common or am I being overly sensitive?

RE: Units, formulas, anyone?

The short answer is that your professor was so full of hot air that it is amazing he didn't float from the room.  When I was in grad school (while working), one of my colleagues asked a question that could best be answered by walking him through the derivation of Bernoulli's Equation.  About half way through, my boss walked by and said "that's the first time I've seen that kind of math since I left college, it better be the last".  He was dead serious.  The statement that "people in the industry won't stand for incomplete calculations" is just wishful thinking (probably from someone who has never submitted a design in real life).  People in industry will accept pure, unadulterated bat guano and then pay someone to unravel the mess you've made (luckily, so far in my practice I've been the unraveller rather than the raveller, but one bad day can change that).

Most engineers I see in industry are simply project managers and rely on others (or programs that they don't take the time to verify which is worse in my opinion) to do their job.  I see a lot of canned programs that may or may not be accurate, may or may not include checks against violating equation assumptions, may or may not do unit conversions correctly.  

Most of my design projects include a printout from a MathCad file (which includes units) and I've never had a company engineer question any of them.  I don't think they even look, but I have no way of knowing.  Doing the job creates the MathCad file and printing it is trivial.

If I had a job checking plans and calcs, I'd check them.  You're the one signing off and if you get plans with inadequate information that is why you check them.  If you require the information that is specified in the contract then one of two things will happen--either you'll start getting complete plans/calcs or your subs will scream so loudly that you'll find yourself in a design job instead of a checker job.  Does either outcome suck?

David

RE: Units, formulas, anyone?

If you do not like the submittals, then don't accept them.  The exercise of you requiring additional calcs or units or whatever will go on until your boss says quit or the submitter says NO.  Then you will be required to explain why no supplier is on the team.

RE: Units, formulas, anyone?

I write dozens of correction letters every year where someone thinks they create their own consturction documents for alterations or even additions of commercial buildings.  They are not complicated, for us in the industry, but these are business owners who have some residential experience, and by extrapolation, their project should be pretty simple.  No HVAC information (none), no lighting, only wall and outlet locations.  "Well, when I built my house...."

I think the availibility and education of people today makes them over confident.  They simply do not know what they do not know.  In some cases, software doing the heavy lifting makes it easier for people to get the information they want, but heaven help them trying to explain how they came up with a member size. Some of the "calculations" I get makes me wonder why anyone would want to take on all that personal liability.

I am not sure if there is a solution, except, prepare a standard template where you cite where it is required (contract, local convention, laws) that they supply the missing information.
 

Don Phillips
http://worthingtonengineering.com

RE: Units, formulas, anyone?

If you  were a civil engineer in Oregon and did not include units you would find yourself out of a job. There are enough calculations in metric and in English units due to difference in supply that you have to specify. There were some very costly examples of this that made our highway department look bad a few years ago.
Also have we forgotten the mars mission that went off to nowhere because one contractor used metric and the other used English? I would say if it doesn't have units refuse to put your name on it.

Luck is a difficult thing to verify and therefore should be tested often. - Me

RE: Units, formulas, anyone?

Seems to be a wide variety of requirements.  There are often requests from Mathcad users to show the equation, then the values substituted into the equation, etc.

Others, like myself, use canned programs with parameter lists that we have to provide, but no intermediate calculations, but that's for aerospace sensor applications.

Then, there's a certain person in the Mathcad Collab that insists that no calculation should be done with units, but everyone pretty much thinks that he's whacked.

If the submitter presents his spreadsheet or Mathcad worksheet, and he certifies that he's verified the calculations, I, personally, would consider that adequate, i.e., without the fancy "display replacement of all the variables with the numerical values," but that's just me.

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: Units, formulas, anyone?

I personally am of the opinion that numbers without units (other than specific density) are theoretical mathematics and cannot possibly represent anything of interest to an engineer.  Equations used should be referenced to an accepted text (Xerox copy of the page included), or shown in the calculations itself, formulas visible when calculations are submitted via Mathcadd/Excel printout, or perhaps not if the Mathcadd file also accompanies the printed pages; my option.  I view a large portion of my job as assuring that the adequacy of the design is not only proven to myself at present, but that sufficient proof also exists in the files such that another engineer in the future will also be able to arrive at the same conclusion.  As such, I request that any incomplete calculations be made complete to my satisfaction and include the appropriate units, and any other evidence I deem necessary.  Fortunately the companies I work for back up my requests because they also view those requests as reasonable and required to substantiate the design.  Of course the degree of completeness that I require varies with the work submitted and my previous experience in similar designs.  At times I have to rely on my knowing where the borderlines are being pushed by the designers and, if they pushed too far against my limits, or the limits of present proven technology, I may consult with collegues for their opinions and I, or we as a group, we will request that additional evidence, proof of the designer's experience with the adequacy of his previous similar installations, corrected calcs, new calculations, or an entire study of the subject design be completed and submitted, if necessary to verify proof of concept and implementation.

"Design by inspection" limits increase with one's experience.  Certainly there are many designs which easily fit into that catagory, however there are those that obviously do not.  The only resonable gages of when additional calculations, studies, laboratory testing, or full scale mockups or pilot plants are needed are one's, or the group's, or the companies experience with the design at hand and the degree to which the design submitted either pushes the limits of that experience, or the limits of existing technology coupled with the level of risk that the design presents verses the level of risk that is acceptable, which sometimes even requires an additional study by itself to determine.

So, my short version is, keep requesting whatever you deem necessary such that you are satsified that the design is acceptable.  If you like units to accompany calculations, ask for them.  Tell them unfortunately they drew the short straw, you're only one engineer and you don't have a lot of experience with that particular design and its both of your jobs to get that thing built.  Let them know that, if they are willing to help you get through the first one, the next approval will go a lot smoother, and if they include the units you won't have to guess what they are, or waste their time asking them to explain it, you'll both be better off in the long run...  and that's just the way life is for now.

"Make everything as simple as possible, but not simpler." - Albert Einstein (1879-1955)
***************
http://virtualpipeline.spaces.live.com/

RE: Units, formulas, anyone?

My opinion is that all equations should be written using strict SI units.  Inputs and outputs can be converted from/to units of choice if required.  Embedding units conversions directly into equations is a bad idea.  I've wasted too much time trying to work out where mystery multipliers come from (sqrt(10), sqrt(1000), 30/PI, 25.4, ...).

- Steve

RE: Units, formulas, anyone?

I had a supplier that gave me the "by inspection" story, with no analyitical or test data to back up the design.  After a week of requests for something to back-up the design, I finally did a basic stress analysis, referenced the equation in Roarks, and just told them the final answer, which was driving a design change.  No calculation, no diagrams, nothing but the final answer; That forced them to actually run a real analysis, and guess what?  The design changed.

Stick to your guns.  Hopefully the design is acceptable, and no design change is required, but from a technical prospective, how would you know?

RE: Units, formulas, anyone?

As you are less than a year out of school it would be wise to listen to your supervisors. With experience comes the knowledge to be able to determine if solutions look right or not, in many cases.
I am not excusing the submission of vague or incomplete calculations, but there are times when "OK by inspection" is perfectly acceptable. Those making the submissions should not have to tailor their calcs. to accommodate an inexperienced checker.

RE: Units, formulas, anyone?

Quote (apsix):

As you are less than a year out of school it would be wise to listen to your supervisors. With experience comes the knowledge to be able to determine if solutions look right or not, in many cases.
Then is he really the proper person to be checking everyone else's work if he has little to no experience?  Sounds like a "post turtle" position.
 

Dan - Owner
http://www.Hi-TecDesigns.com

RE: Units, formulas, anyone?

The goal is an agreement that the design works, whether an inexperienced engineer designs (more often the case) it, and an experienced engineer checks it, or v/v.  All sbmissions necessary to reach that agreement need to be requested and made.  Anything else is positively not acceptable.  Agreement is paramount.  Everybody in that situation needs to be satisfied or somebody isn't doing their job.

"Make everything as simple as possible, but not simpler." - Albert Einstein (1879-1955)
***************
http://virtualpipeline.spaces.live.com/

RE: Units, formulas, anyone?

All analysis and design needs to stand on it's own.  Not dependant on the back of some old guys grey matter.

RE: Units, formulas, anyone?

Giving a design to a new engineer to check has advantages and disadvantages.  I've found that what is considered and documented in the calculations is checked rather well, questions are asked and answered, the new guy sees how calculations should be done and the experienced guy gets a pretty good exercise in better understanding how to make clear and concise calculations and a good review on his knoweledge of theory too.  The disadvantage is that things that might should have been considered, but do not appear in the calculations being checked, can get missed entirely.  So, I would hope that only the routine designs that don't overload a new engineer's experience level would be given to the new guy on the block more as a training exercise than anything else.

"Make everything as simple as possible, but not simpler." - Albert Einstein (1879-1955)
***************
http://virtualpipeline.spaces.live.com/

RE: Units, formulas, anyone?

(OP)
All of my reviews are passed on to the PE before getting signed.  They usually come back and point things out to me that they think are important to make sure I had considered it.

I don't think that my inexperience is to blame.  I feel capable of doing most of the designs myself (calculating loads, finding capacities, ect.) but I'm not the one who was hired to do the design.  If complete calculations aren't included I have to try and back calculate to figure out what they did, checking code requirements for wind velocities for example.  I'm afraid I don't see the connection between an inexperienced checker and not providing adequate calculations to check.  Is telepathy a requirement for an experienced checker?

I agree wholeheartedly with monkeydog.  Every design needs to state everything pertinent.  Saying a bracket can resist the XXX lb load doesn't give any insight to where a load came from, what loads were considered, the capacity of the bracket, anything.  Everything should be provided to reproduce the numbers.  If it's not provided you can't check it, only assume it.  I don't think I'm asking a submitter to tailor their calcs for me, I think that a lot of submittals don't get checked the way they should and submitters are getting used to not spending the time to make a complete package that isn't going to be throughly reviewed anyways... but that's just my inexperienced view.  Is it really that unreasonable?

RE: Units, formulas, anyone?

For calcs, I'm guilty of often just quoting the standard and leaving it there (but I do label my inputs etc).  

But, it's not to say the proper calcs weren't done, it's just that with a "standard" design, it's almost clear what the numbers are to an experienced eye.  
You do state you are fresh out of school.  You may find that older reviewers may simply know what's right/wrong on rote designs based on experience, and likely older engineers are likely in the same boat.  

Be aware that having a young guy come in and demand detail calcs on what (to others) is a basic design is likely to get you labelled - best case - as a pain.

 

-
Syl.

RE: Units, formulas, anyone?

Seems like if there is a standard calc, for a standard design, even a simple annotation could be made such as "refer to Roarks table x, equation y, loads are z lbs".  But if all you get is "OK by inspection", that seems a proper response is "Inspected found flaw".

RE: Units, formulas, anyone?

While using a hatchet where you need a scalpel is inappropriate, the reverse is also not appropriate.  When producing calculations, include sufficient units, equations, references such that when you see it five years from now, you can still follow.  Expect the same from the submitters.

RE: Units, formulas, anyone?

(OP)
I can appreciate standard designs, and as long as it looks like there is an understanding of the conditions I don't say anything.  I have only once returned a submittal because my check on their design failed.  Turned out that they were using a standard template and didn't update it for the wind zone the building was in.  Other than that I try to run my own numbers if I can't use theirs, if they come out similar I don't say anything.  It would just be quicker and easier if we didn't both run through all the numbers.  I'll save my demands for when I'm a little more established.

RE: Units, formulas, anyone?

Many engineering companys do not allow a checker to do seprate calculations, logic being you then simply wind up with two unchecked designs!

"Make everything as simple as possible, but not simpler." - Albert Einstein (1879-1955)
***************
http://virtualpipeline.spaces.live.com/

RE: Units, formulas, anyone?

Quote:


I can appreciate standard designs, and as long as it looks like there is an understanding of the conditions I don't say anything.  I have only once returned a submittal because my check on their design failed.  Turned out that they were using a standard template and didn't update it for the wind zone the building was in.  Other than that I try to run my own numbers if I can't use theirs, if they come out similar I don't say anything.  It would just be quicker and easier if we didn't both run through all the numbers.  I'll save my demands for when I'm a little more established.

In a way, you are likely learning more and becoming better at your job doing it this way than if you did have the numbers fully and weren't forced to dig.   

-
Syl.

RE: Units, formulas, anyone?

I can appreciate that the response to this thread from an (Aerospace) would differ from that from a (Structural).

RE: Units, formulas, anyone?

True, in Aerospace, you have one chance to get it right.

RE: Units, formulas, anyone?

As a government employee (State), there has been many times when I have requested additional information from a professional engineer over his calculations that did not include formulae, units, assumptions, sources of data.  
I am not saying that the calculations are wrong, but did not contain sufficient amount of information for my review.  Sometimes I'll be able to halfway follow what was being performed, and the request is to verify my assumptions.

Any engineer who is not willing to provide the basic information for calculations (e.g., formulae, units, sources) is one who is wasting the time of others who need to review their work.  And he better pray that something critical is never missed due to his negligance (e.g., resulting in deaths or million $$ project).

RE: Units, formulas, anyone?

(OP)
I guess thats what gets me the most.  I don't really mind doing the checks or running the numbers (in fact, its kinda fun, like a jigsaw puzzle with problem solving), it just seems to me that a design without usable calculations isn't complete.

For example, this may be an extreme case?  A building owner came to us, when he was trying to sell two warehouse type buildings, for a structural evaluation.  Pretty basic pre-engineered steel buildings (approx 60'x120'), and a local engineer had done the foundation.  The buildings had been up for around two years.  I went out to the site, took some pictures, looked around, everything looked good in building #1.  Building #2 was identical except he had had a two story timber framed office built inside at one end (approx 20'x60').  Apparently the contractor did the design and fabrication but I got rough layouts/dimensions/materials knowing already that this was going to be a problem.  Got back to the office my boss told me to check the foundation calcs and do a seismic evaluation of the inside office structure since we had no previous calcs for that.  The previous engineer that had designed the foundation was vague in his calculations (approx 4 hand written sheets with diagrams for the entire foundation).  The loads were given by steel building manufacturer but still needed to be combined (as was explicitly stated in the building manufacturer's drawings).  As best I can tell the foundation engineer did not combine the loads and just picked the biggest one.  He had drawn very nice moment diagrams for the grade beams, but how were they calculated?  No idea, mine were much larger.  In fact everything I calced was on the order of 1.5-2.0 times larger than the previous engineer (moments/shears/bearings).  At the start my boss told me that this guy has been around forever and he wasn't worried.  I tried to do all the back calculating I could figure out but came nowhere close to what I felt like was a legit design.  My guess is he has done it a million times, second nature and basic to him.  The "shearwalls" in the office building on the short sides had less than 10' to develop the shear resistance, 1/2" gyp board nailed to cut 2x4's (cut to fit around and inside the channels holding up the exterior siding) was inadequate (to say the least) of carrying anticipated seismic forces in a place where seismic design can often control (Alaska).  My boss had me write a report that detailed out the deficiencies I found with my calcs (approx 20 handwritten sheets without drawings), don't know what happened with it beyond that.  I can only hope that I was wrong (and that somebody checked MY calculations!).

RE: Units, formulas, anyone?

An engineering package shall be self-contained and in itself, fully describe the engineer's design.  It is not acceptable if a "competent" reviewer has to physically communicate with the engineer to understand what he is doing.  At the same time, it is not the rold of an engineer to "train" the reviewer.

RE: Units, formulas, anyone?

2
"True, in Aerospace, you have one chance to get it right. "

I'd argue the opposite. In aerospace and automotive we have comprehensive test programs so that any initial errors by the engineer are caught before Job 1.

These structural guys don't have test programs, and the prototype /is/ Job 1. That's why design to code is such a strange paradigm to us, and optimal design for function is such a strange paradigm for them.

 

Cheers

Greg Locock

SIG:Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.

RE: Units, formulas, anyone?

True, once the baseline design is qualified, you should have screened any engineering errors.  But, engineering modifications to the design does not necessarly result in requalification of the design.  Also the margins to failure could result in catatrophic failure with the exception of manned programs.

RE: Units, formulas, anyone?

I have mixed feelings about this whole issue.

First off, it seems that the purpose of the calculations is to do the design.  The calculations are not intended to educate those unfamiliar with the topic.  You should not request calculations and expect a textbook.

What is the purpose of submitting calculations for review?  As best I can tell, in most cases, it is just a "feel good" thing to see that the calculations exist.  The ones requesting the review have no idea how the calculations ought to work.  You can quote equations and plug numbers in them, but you could quote different equations and get different numbers and nobody would notice the difference, just so the numbers match the equations.

If there is to be a technical review for accurary in the calculations, it needs to be by someone thoroughly familiar with the topic, not a matter of handing them over to "the new guy".  Unfortunately, this seems seldom to be the case.  Professional competency is critical when preparing the calculations, but is thrown out the window when reviewing them.

Through experience, I have learned that the more detailed and complete the calculations are, the more likely you are to have criticisms of minor issues and have to go back and forth on that.  So the best strategy from a submittal standpoint is to just omit all the minor items from the calculations, give the reviewer a few major items, and everyone's happy.  The one exception to this rule is when you have extensive spreadsheets or computational analysis results, which nobody is expected to check anyway.  But don't assume that the calculations you review are all that were done for the job- that may or may not be the case.

Additionally, part of engineering judgment is knowing what to calculate and what not to calculate.  Anything that can be designed, can be designed to any desired degree of complexity.  If NASA designed houses, they would have a dozen engineers spending a year on each board.  When the work requires an experienced engineer, and that experienced engineer says item X is okay by inspection, you are getting part of that experience that you payed for.

RE: Units, formulas, anyone?

The bottom line is that if you are approving something then do not put your name to it unless you are satisfied that the calculation stands up to scrutiny. No engineer should be expected to rubber stamp someone else's work - it's unprofessional.

Would you rather ask pokey questions (and face a little heat for doing so) or be being asked them by a lawyer when something has gone pear-shaped and the buck stops with you?

No more things should be presumed to exist than are absolutely necessary - William of Occam

RE: Units, formulas, anyone?

I agree with JStephen.  Review of anything, ideally, should be done by someone of equal or better caliber.  Of course, it is very subjective.  As a minimum, PE's work should be reviewed by a PE and SE's work should be reviewed by an SE, which isn't the case in many jurisdictions.

Submitter should not prepare the calculation package in an effort to educate the reviewer.

RE: Units, formulas, anyone?

When I've been asked to review a design, I usually check to see that all the info for construction/or whatever is presented and add procedures as required.  I then do a preliminary design using a methodology that I'm familiar with to see that the values are in the same ball park.  It is very seldom that I check items by reviewing the actual calculations prepared by someone else, except if I encounter something that doesn't seem to fly and I'm trying to find out the reason for the discreptancy.

Dik

RE: Units, formulas, anyone?

SKIAK - ask for what ever you need.  I've been a state regulator for about a 1/4 of a century (that puts some labels on things).  Starting out in the Water and Wastewater fields, now just in Water.  Even with a preliminary conference in which we tell the  consultants what we expect in the way of submittals, I'd say only 10% to 15% are approvable on the first submittal!
Yes, I started out reviewing more experienced engineer's work, but not only was I requesting changes; but at that time my work was checked by a PE.  Now that I've had my PE for two decades, my work is still checked by another PE.
Dixon

RE: Units, formulas, anyone?

Greglocock!
While I agree that your statement above is accurate, I have to say that the "optimal design for function" theory is what gets those cars today totaled at 5 MPH, compared to when they made them solid (i.e. to code).
In 1993, the first Trade center bombing did not bring the towers down, thanks to the "design to code" and not "for function".
 

RE: Units, formulas, anyone?

I also believe the varied opinions are indicative of industry expectations.  Even in structural engineering, there is a big difference between the building industry and the bridge industry.  Also, there are different expectations for turn-key products vs. bid designs built to plan.

For my part, I have designed many things, and I have reviewed the designs for many things.  I look it over, and tell my boss what I think I will need.  He either buys in or he changes my opinion.  Most of my bosses would rather let me handle it my way than get involved.

I often will spot check a few numbers along the way.  If I can't get anything from the calcs, then I'll ask specific questions to get clarification.  If they can't answer my questions, then I have to question if they can even do a design.

I have caught some catastrophic errors in the past.  I never take that job lightly.

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