I'm wondering Hand Calculation 2

[envc77]

First of all, I'm sorry that i can't speak english very well. I hope you to understand me.
I have done structural engineeing(mainly bridges) for about five years.
when i seen this forum, there are a lot of people say hand calculation is important.
I wnat to do calculation because my job was mainly to draw structures.

I think the calculation is to run special software.
I surprise that to do pre-design is possible by only hand.

And. I'm very wondering how to do hand calculation.

I would appreciate that you give me any suggestion or how to do hand cals.

 

[IRstuff]

The hand calculations assume that you've taken a course of study in the relevant engineering disciplines. To use those equations without understanding their context and limitations could get people killed.

If you don't have the educational background, then you need to get it. Anything else is a danger to you and others.

TTFN

FAQ731-376

 

[Twoballcane]

If you mean calculate like FEA software or similar that is a study in its self, but if you are talking about taking what you learned in Uni (or college here in the states) and apply it to your problem that is hand calculations. The trick is to break down your real world problem so that you can apply the theory and equations you learned in school. The caveat is that you’re trying to simulate not get real answers like test data.

As IR said, if you did not get trained to do this, don’t try to attempt it with out the proper education.


Tobalcane
"If you avoid failure, you also avoid success."

 

[shin25]

A good engineer should be able to verify by hand calculation that each and every number in a software print out is accurate.

Computer softwares are engineering tools (just like calculators) and out there just to save time. Ultimately, you are the designer and take full responsibility for the outcome of the design using computer.

As a competent engineer you must be able to verify the design by hand. If you cannot, then you may need more mentoring.

 

[MintJulep]

A good engineer should be able to verify by hand calculation that each and every number in a software print out is accurate.

I think that is going too far. It may be possible - in theory - but the shear number of calculations performed makes it impossible in practice.

A good engineer will be able to tell you when the pretty pictures that the computer spits out don't look quite right. Hand calculations may be involved in this, although quite often it is possible just by visual observation of the plots. Then some digging is required to find out where the model is flawed, or the boundary conditions wrong.

 

[KENAT]

I'm from the school that most of the time FEA results should be verified by another method. Be it 'hand' linear calcs or testing.

Now the hand calcs don't have to be a perfect match, in some situations I've had experienced guys accept just the same order of magnitude.

envc77 I'm trying to make sure I/we understand your post.

1. Do you have the equivalent of a bachelors degree in relevant engineering field?

2. You say your job was mainly to draw structures, does this mean you are more of a designer/drafter/CAD operator than an Engineer?

3. When you say to run special software do you mean Finite Element Analysis (FEA)?

I agree with what others say about needing to take a relevant course. I also strongly agree with shin25 about the mentoring aspect, what you learn in college is a foundation, applying it in the real world is often a bit different. There are 'applied' courses to help but having a more experienced colleague to work alongside is invaluable.

KENAT, probably the least qualified checker you'll ever meet...

 

[Ashereng]

I am in accord with Mint. To do pressure calculations in a pipeline system by hand would take a loooooong time. That is why we have computers, software and similation packages.

Having said that, a competent engineer should know when something is "really out of whack". Also, a competent engiener should be able to do some quick "back of the envolope" calculations to determine the order of magnitude correctness, with some simplifying assumptions (valid ones of course). Being able to do one or two iterations by hand is also a sign of understanding - if you can do one or two, you can do the rest.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[Gymmeh]

The question you asked may be a little to complex to be answered by using a forum.

Knowledge of this is required by Professional engineers in the USA.
If asking a Professional engineer (in the USA) or the equivalent in any other country may be the best option.

For equivalents to a Professional engineer
see <

http://en.wikipedia.org/wiki/Professional_Engineer>

 

[whyun]

I agree with the gist of what shin25 stated. To perform hand calculations for a complete structure, all individual member sizes and their connections subject to all possible load combinations is not practical. However, true engineer, given unlimited time and resources should be capable of replicating the computer results by way of hand calculations. Better engineer finds errors in the software and inform the software companies actually. Commercial software are not error free.

 

[KENAT]

Most stress guys I've worked with would usually look at the system and determine the 'worst case', ie areas with highest stress. They'd then typically only 'hand' analyze these areas in detail.

With FEA you are normally looking at the entire part/system not just one area.

KENAT, probably the least qualified checker you'll ever meet...

 

[IRstuff]

You guys seem to be missing the point.


The OP does not appear to be a trained engineer.

TTFN

FAQ731-376

 

[ctopher]

envc77,
You write that your main job is to draw bridges. As others had written, this tells me you are not an engineer. To design bridges, you need the education and a PE license.
I hope you do not design bridges, and build them, for every one's safety.

Chris
SolidWorks 07 4.0/PDMWorks 07
AutoCAD 06
ctopher's home (updated 10-07-07)
ctopher's blog

 

[jmw]

I was taught long long ago that if you couldn't do an order of magnitude calculation you would never know if the result you got from a calculation was right or wrong.

When Shin25 says you should be able to do every calculation, he didn't mean (I think) that you would do every calculation, just that you could, if you had to.
It is part of understanding what is going on.

A computer is a tool and it is either a damn good tool or p*** poor depending on your understanding.

As a tool, a good software program is designed to take the grunt and time consuming graft out of the engineers work; not replace the engineer.
Just hope HR get the right message on that but I'd guess I might be in a minority here as I would guess there is many a drafter out there using CAD that wouldn't know which hand to hold the pencil in.

JMW

http://www.ViscoAnalyser.com

 

[Gymmeh]

I am with IRstuff...

The OP refers to designing bridges... something that involves people safety is NOT to be learned over the internet. He needs to meet with someone; professor, PE, or the likes there of, to teach him.

 

[jeebusmn]

Assumptions are made to grossly simplify the problem. Often being within a power of 10 is enough to give a fair understanding.

 

[Twoballcane]

OP: "I think the calculation is to run special software."

Im wondering if s/he is asking if you can do the software calculations by hand. If this is what s/he is asking, this is posible, but you will have to really understand your engineering concepts and then apply them to a matrix calculation which is not to bad to do because most calculators can do matrix calculatins, but just the shear number of points you will be calculating is cumbersome. I did it back in my college days. Once you do a few, you really appriciate the software crunching the numbers for you.

Tobalcane
"If you avoid failure, you also avoid success."

 

[KENAT]

I'm not missing the point, if the person doesn't have the appropriate education/training/qualification they shouldn't be playing around and/or trying to teach themself.

However, the OP makes it clear that their English may be poor so before we make too many assumptions or pound the OP I think we should try and get clarification.

KENAT, probably the least qualified checker you'll ever meet...

 

[envc77]

I would like to reply to KENAT's question.
1. I have a bachelors degree in civil engineering field.
2. I'm not a just drafter.
70% of my job is to draw structures but remainder is to calculation
(I use only computer software and excel but I can't do hand calculation. and I was wondering..)
3. I used frame model calculation software (It's name is MIDAS)

I just want to comprehend my works by hand.

 

[IRstuff]

And you got a BSCE without doing any hand calculations?

TTFN

FAQ731-376

 

[Gymmeh]

Okie, my bad KENAT. Before Jumping...

Envc77: What specific information are you makeing the calculation(s) for?

Deflection? Failure point(s)? Welded/bolted Connections? etc.