## Hand Calculations

## Hand Calculations

(OP)

I am curious how many people still do hand calculations for structural analysis and steel design, or know of someone who does? Things like moment distribution, combined stresses, and so on. When are hand calcs appropriate, or not. Does anyone have opinions about this?

Just wondering.

Best Regards,

-Mike

Just wondering.

Best Regards,

-Mike

## RE: Hand Calculations

The engineers who review my work (in-house and the occasional plan reviewer)seem to appreciate the hand calculations. Not so much "black box" engineering. Plus with hand calculations, I usually do sketches that explain the design.

I'm afraid I'm the last of a breed. I can get away with it because I'm a senior level employee, but the younger engineers are afraid hand calculations and sketches slow them down.

## RE: Hand Calculations

For a one-time simple project, hand calcs are fine.

For simple calcs that require references and explanations, etc., I've actually made "word" documents, and it's fairly quick to go through and change the numbers for the case in point.

Spreadsheets work great for lots of things- anytime you're doing the same basic thing several times over. I've done a couple using visual basic (took that as continuing ed for pe licenses), and that can be pretty cool.

## RE: Hand Calculations

also design a PT & RC concrete with a lot of functions , and currently it is my basic tools in prelaminary design befor going to a FEA software.

from while to another i trying to improve these sheets and i found it a good replacement for the hand calculation.

## RE: Hand Calculations

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OK, off the "bandwagon"...nice to see some people still remember how to calculate a beam.

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I still do a lot of calcs by hand but will use software when I can. I have been writing programs in BASIC and VisualBASIC for about 20 years, and I like VB, but these are very specific in function. About two years ago I bought a calculation program and find that now I am doing less with VB and more with the calc program. These programs (these are several good ones) are more of a free form type of calculation sheet that is something like using MS Word but with the ability to solve equations.

It has occurred to me however, that even though I am using software, my approach and thought process is really the same as hand calcs. And I like this. I get to select unbraced lengths, K factors, column braced lengths, etc. It's all pretty neat, in my opinion.

I am now shopping for another FEA program, but as much as I want to get a program for analysis and design, I can't bring myself to buy into the "black box" approach. But I get the feeling I'm doing things the hard way, again.

-Mike

## RE: Hand Calculations

Personally I wish my company would buy us MathCAD and/or MATLAB. I use these at the University and would love an opportunity to take advantage of what you can do with these programs. They seem to have much more to offer than a spreadsheet with the same hand calc feel to them that mrMikee mentioned.

## RE: Hand Calculations

I use CalculationCenter ($595) by Wolfram Research and my son uses MathCAD ($1200). They are similar but different. There's and interesting discussion on thread770-122493, but it's not my intent here to start that one over again. I too like the hand calc feel this software gives me.

One thing I noticed about RISA is that it only checks single angle struts for L/r. Compression in single angles is much more complicated than this, which is one of my pet peeves. I've seen too many engineers not figure this correctly.

jmiec: You mention that you hate software that you didn't write. I too suffer from this affliction.

Thanks,

-Mike

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-Mike

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I also use Mathcad whenever I can because after the checker looks everything over, all I have to do is change one or two values and the whole thing updates itself. My only regret with Mathcad is that I can't easily place sketches in the work. If I did more projects that were similar geometry, I could smoke some work with all the little worksheets I have now.

Like you, I basically do everything possible by hand. I have been working on a Mathcad worksheet that analyzes a straight multispan girder with varying moment of inertia. It is fairly far along but still has a way to go. We use Mathcad 2000 Pro here in my office, and I have a copy of Mathcad 7 Pro at home.

The secret to solving this problem (say your three span continuous girder) is to realize that it can be formulated using a stiffness model with only two indeterminant degrees of freedom. Once you have the end rotations, you can immediately obtain the end moments for a specific load combination. With the end moments, everything else is analyzing a simply supported beam.

The key to getting the problem down to two DOF is eliminating the nodes where discrete changes occur in the MOI. You can accomplish this using the Hardy Cross Column Analogy. This is a method where a beam vith varying MOI can be reformulated as an equivalent beam with differing rotational stiffness at each end (e.g. the stiffness of the new beam will not be 4EI/L at each end as it is with a prismatic beam). With the rotational stiffness, the remaining translational stiffness and coupling values can be computed directly from the equations for static equilibrium.

Anyway, when you can reduce the problem to so few DOF, you find there are not so many load combinations to worry about. I have conquered the moment design portion and I am working on the fatigue stress and shear portion of the design.

Unfortunately, I have spent many hours on this, much of it my own time and I am not inclined to give the thing away. But if you know what the Hardy Cross Column Analogy is and know how to use Mathcad and the stiffness method, you can make a worksheet to do the same thing.

Good Luck - Ed

## RE: Hand Calculations

Thanks for the suggestions. It sounds as though the approach will work and I'd love to try it. Clearly though, the solution will take many hours, so it won't happen for a while. Anyone who has spent long hours to develop a solution can appreciate your reluctance to share it. The approach itself is very valuable. I have used stiffness solutions for small frames, but used the 3 moment equation for continuous beams.

To place sketches in a MathCad sheet, you can import AutoCad or Microstation drawings. It you use some other electronic drawing program that doesn't talk to MathCad, there is a handy little utility called "Capture Express" that allows you to cut and paste pretty much anything. I suppose you could even make a hand sketch, scan it, and use the capture utility to paste it into Mathcad.

Jim

## RE: Hand Calculations

I'm glad you understand about the time factor, but I'll check back from time to time in case you get stuck while you work on it. I usually check this forum twice a week.

I usually draw free body diagrams by hand and scale sketches of connections and the like if I have the time and then I just photocopy them in or scan them and place them as an object. If I used the worksheets more frequently, then I would take more time to get the figures in the file.

Good Luck - Ed

P.S. Do you have the booklet,

Moments, Shears and Reactions for Continuous Highway Bridges, published by AISC? That's what I used to check my first run of the procedure. I don't know if it is in print, but you might try contacting AISC if you don't have a copy. All us Hand Calc guys should have a copy if you do bridges. My information says it costs $16 and you can reach AISC @ (312) 670-2400.And for those of you who do have it (1986 ed.) there is an error in Table 2.0, max dead load moment @ B should read -0.1250 and not -1.1250. In Table A2.0 the value in column 0.6 of span 1, row 0.8 of span 2 should read -0.0288 not -0.2088. I have not done an exhaustive check of the tables, these are just two values I have noticed that were incorrect (typos).

## RE: Hand Calculations

I was able to order the booklet from "Out of Print" documents at AISC's Web Site. But the version they list ($10 for members)is dated 1970, with no updates available.

Thanks for the tip.

Jim

## RE: Hand Calculations

Wait till you get it, you will wonder how you ever got along without it. Let me know when you get around to setting up the Mathcad worksheet on the three span continuous problem.

Good Luck - Ed

## RE: Hand Calculations

## RE: Hand Calculations

We make extensive use of ENERCALC as a check of hand calcs and software output from the modeling software. Most of us use tons of MathCAD templates and Excel spreadsheets for repetative design processes, like torsion in concrete beams, snow loading, and anchor bolt connections, to name a few.

Also, whenever I personally run into something that is unique, like FRP reinforcement for example, I prefer MathCAD to spreadsheets because I can easily track the process of design and analysis. Most of my templates are crammed with notes and references to Code requirements and textbooks. Most of use tend to whip up a quick diagram or sketch to include in those templates to clarify input/output too.