Units, formulas, anyone? 4

[SKIAK]

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?

 

[zdas04]

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

 

[civilperson]

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.

 

[DonPhillips]

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

 

[carnage1]

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

 

[IRstuff]

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

 

[BigInch]

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)
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[SomptingGuy]

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

 

[monkeydog]

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?

 

[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.
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.

 

[MacGyverS2000]

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

 

[BigInch]

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)
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http://virtualpipeline.spaces.live.com/

 

[monkeydog]

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

 

[BigInch]

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)
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http://virtualpipeline.spaces.live.com/

 

[SKIAK]

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?

 

[SylvestreW]

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.

 

[monkeydog]

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".

 

[whyun]

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.

 

[SKIAK]

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.

 

[BigInch]

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)
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http://virtualpipeline.spaces.live.com/