Communicating structural calculations 13

[spaderess]

There is a disregard for the handicraft of writing and performing legible sequences of calculations in my immediate context. Trying to check or re-use even my own, let alone others, calculations is a pain.

I have been looking into literature or standards in an attempt to better this. Yet, most of the stuff I found is centered on general mathematical writing and therefore not as applicable. The only books I found directly dealing with the specific problems are Robert Motes books The Engineers Word, and The engineers Tables. Standards, on the other hand, seems to be specific to firms and not accesible from the outside. This lack is surprising, coming from an architectural background, where all aspects of drawings are highly standardized.

Therefore, my questions are these.
1. Are there any literature or widely available standards dealing with presentation and/or performing of structural calculations?
2. Do you know of any examples of sets of calculations available, to be used as a best-practices-example?
3. What do you consider to be essential qualities in regards to clarity when checking others calculations?

 

[KootK]

I used to be the biggest MathCAD proponent around. Less so now.

- Crap backwards compatibility.
- Bought out by big parent company.
- Expensive. They just ditched perpetual licensing and subscription is $600 US per year.
- Somehow, Prime 4.0 still doesn't have as many feature as V15 had back in 1859.

SMath Studio is looking better all the time. I know it has some limited programming features which is great. Does it have things like goal seek and hidden regions? Talkin' to you rn14.

I'm more than a little bitter about MathCAD really. Around 2000, I placed my bet on MathCAD being the future and let my Excel skills slide. I regret that choice intensely now. Trust. That is what is now absent from my relationship with MathCAD.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[dik]

KootK... I use SMath Studio and find it pretty useful. Not as many bells and whistles as MathCAD, but totally functional.

My new TI calculator is proving to be very useful... it does a form of 'pretty print' and I can print the files to a *.pdf file for saving. Can add comments or can just do 'meatball' calculations... it saves them all. It has a spreadsheet that easily rivals excel and for more complex operations.

MathCAD went downhill and the price soared when it was taken over by the 'bigname' company.

Dik

 

[kingnero]

Nobody uses the MS Word plug-in/add-in "Equate" (

http://www.wordequate.com/

) ?

---

http://be.linkedin.com/in/fusionpoint

 

[dik]

Neat, pretty much like my TI calculator... does Excel take the data from the formulae? or do you have to key it in separately?

Dik

 

[IRstuff]

That looks to be even better than MathLook.

There's a bit of a Mathcad flavor in a couple of the examples. Their website's a bit clunky, though

Thanks

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[JoelTXCive]

I have been using the Smath studio also. Once you get the hang of the input style, it works well. (i just wish you could change the native units to pound, feet, inch instead of always defaulting to SI units)

I usually scan diagrams/sketches into a PDF format or Jpeg. Then I use windows free screen snipping tool to cut and paste into Smath.

The best thing about Smath studio is that it is free!

 

[Archie264]

I’m a bit contra-wise to many in that I loath MathCad output but like Excel output. But, that said, the point of the Excel output is high-production, say, for example, designing wooden beams or joists. It must be verified as accurate with the results back-calculatable but not necessarily pretty. MathCad, on the other hand, looks to me like mathematical derivations of formulas and it hurts my eyes. Of course, for me nothing is better than hand calculations. Just my opinion.

 

[IRstuff]

" MathCad, on the other hand, looks to me like mathematical derivations of formulas and it hurts my eyes. Of course, for me nothing is better than hand calculations. "

These seem contradictory; Mathcad, at its basic level, essentially does "hand" calculations and documents them as you go along. There may be something to be said about doing them on a calculator, but Mathcad allows you to avoid making mistakes in unit conversions, etc.

How do you document your hand calculations? Do you write them on a sheet of paper?

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[Archie264]

It doesn't seem contradictory to me; to me hand-written calculations don't have the visual rigor and formality of the MathCad calculations that I've seen. I'm referring to multiple numerators and denominators with super and sub-scripts, exponents, all the units documented in each equation...all very cumbersome to my eyes.

Like I wrote, I know I'm in the minority on this one. But I also prefer wooden pencils to the mechanical ones, wood furniture to particleboard furniture, unlined leather boots to goretex ones, brick vs. vinyl siding, homemade pies to store-bought ones, manual transmissions, rear wheel drive, etc., etc...

 

[MotorCity]

right on Archie246.....add copper to pex waterlines to your list

 

[IRstuff]

OK... it just seems to me that documenting with pencil/paper would result in duplicate work and potential for transcription errors.

I try to do as much as possible where I avoid hand entering numbers more than once. Everything after the initial data entry is copy/paste only.

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[cliff234]

Hokie66 said, “Don't just include a bunch of numbers in your calculations…”. Heck I don’t even see a bunch of numbers in some of the submittals that we get. The last calculation package I reviewed just listed a bunch of equations with symbols that were not clearly defined, with a magical “answer” at the end. The only way I could verify any of the numbers was to do my own calculations. In the “old days” (ten years ago), we would usually get calculation submittals that were easier to follow.

On the other hand, we also sometimes get reams of paper with nothing but numbers. (Equally useless.) Manual calculations are becoming a rarity. This is not good.

I don’t want to “process” calculation submittals. I want to review them to be sure that the person who did the calculations has a clue.

 

[cliff234]

MonsieurR,

You sometimes take a little extra time to intentionally make your calculations confusing and difficult to understand? Respectfully, that is not a good thing to do.

Unfortunately these days, it seems many engineers don’t intentionally strive to make their calculations undecipherable. They are just naturally a confusing mess.

 

[dhengr]

Cliff234:
If you were bashful about say it, I’ll add a couple sentences to the end of your last post. The calcs. are a mess becuase the people doing them (engineers?, come on) don’t have the vaguest idea what the hell they are really doing. They have no engineering experience or judgement to guide them, they have no intuitive understanding of how the structure works, they don’t seem to have a boss that gives a damn or gives any meaningful guidance, just get er done and out the door. We have E&O insur. to cover the rest, or any problems you produce. They can’t do the problem or analysis long hand, they just don’t know how. They couldn’t do it without the software they were given to use, and they really don’t understand how to use that software, or model the structure, or how to interpret its output either. So, you get a ream of paper with numbers on it, and it is the old saw..., ‘dazzle them with data, baffle them with b.s., and maybe they will go away.’

 

[SwinnyGG]

right on Archie246.....add copper to pex waterlines to your list

Off topic but this made me laugh.. I just had my house re-plumbed; the estimator came and gave me a quote on the spot, in writing. I looked it over for 10 seconds and asked him to re-estimate using copper line and fittings instead of PEX.

He looked at me as if I'd just told him I was born on Venus and wanted my home's plumbing to be constructed from chocolate and vanilla frosting.

Back on topic..

As usual for any post I write in the SE forum, I deal with a reasonably different scenario; much of the calculations I deal with are either FEA results or quick calculations of a small aspect of a system.

My approach is always the same- I don't ever read a ream of calculations line by line looking for errors; I just take the same inputs, units and assumptions (or model and conditions if we're talking simulation) and see if I get the same result.

Granted, repeating the work is maybe not feasible for something like evaluating the engineering of a whole building, and there are other drawbacks with this approach; but I've found that if I take a couple of pages of calculation and start stepping through line-by-line, it can often become difficult to avoid getting locked in to the other person's assumptions when they may not be correct.

This, of course, requires that me and the person I'm backing up or evaluating have access to all of the same tools and documentation, which again may not be possible if you're evaluating things after the fact.

 

[12345abc6ttyui67]

As others have said, don't just splat a load of numbers on a page. Lay it out sensibly, describe what you are doing (words and sketches) and use a program which illustrates the calculations when printed (e.g. not excel in it's basic format).

For 'simple' calcs I will usually just overmark the design drawing and add any checks at the side.

For 'moderate' and 'difficult' calcs I will do something like below using MathCAD.

Intro: Describe the project, what I am checking, any obvious constraints, problems. Why I'm going it the way I am doing it.

Methodology: Only for complicated / long calcs, I'll include a step by step break down of what I'm about to do so the checker is forewarned.

Assumptions: Any assumptions go here.

Loading: Details of the applied loads, load cases, factors etc.

Structural System: Describe how the loads are transferred / resisted. Sketches!

Calc Part 1: Brief text description of what I'm checking, sketch if required (I try and work from the applied load to the foundation, checking what's relevant as I follow the load path). Calcs, with descriptions next to each parameter / equation to aid understanding.

If I do any computer modelling etc. then I will include screenshots from the model, showing e.g. geometry, section sizes, applied loads, bending moment / shear etc. as relevant, utilisation plot.

I do usually rely on the checker poking at the model a little bit as well as reading the calc report.

etc.

Conclusion: State what has been checked, what is OK, max. utilisations, etc. Any restrictions on use (e.g. max. load of 5kN/m2 only) etc.

Appendices: Drawings, reference data, print out of relevant pages of standards, etc.

 

[cliff234]

dhengr, You hit the nail on the head. Many "engineers" don't have a clue as to how to confirm via manual calculations whether their computer analysis is correct. I believe that if an engineer can't validate their computer analysis with basic manual calculations, then they should not be using that structural analysis software. Would we let a young pilot fly an airliner if they no actual experience flying planes, but they did have a lot of experience "flying" with their computer flight simulator software at home?

 

[P205]

Unfortunately, because hand sketches take time and force folks to go non-digital, they seem to get used too sparingly. Clipping and pasting sketches into some kind of digital scratch bad seems to produce excellent results. As an example, a rockstar EIT that I used to work with would give me calcs like this:

- Load casing done in matrix form so that you could easily see what when into determining max/min without having to wade through the results of every combo.
- Pasted snippets of the code provisions where it wasn't completely obvious what code provisions had been drawn upon. Folks mostly have access to digital codes now so it's easy.
- Snippets of the framing plans with hatching showing the trib areas for beams. Same for columns with snips of the architectural sections to show unbraced column heights.
- Snippets of SAP2000 results. Moment diagrams, deflections etc.

KootK, can you describe this in a bit more detail? What were they clipping sketches/code provisions into - MS Word file, MathCAD? Could you post a sample by chance?

What I like is doing all the wordy parts of a particular design (say, designing a steel beam-column) with a sketch by hand on design paper, then use my typical beam-column Excel spreadsheet to do that actual computations/code checks. THEN, write on the excel print out any notes or relevant info, and finally staple the pages together.

 

[FE_struct1]

Regarding point 1: A while back my supervisor shared with me a document titled 'Model procedure for the presentation of calculations' by the Concrete society (technical report '5' I believe). It's a fairly old document but it did present a rather systematic way of documenting calculations. It may be the thing you're looking for.

 

[IRstuff]

There's this:

http://shalikamanoj.weebly.com/uploads/1/0/9/1/10917131/65160297-designed-and-detailed_1.pdf

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