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Is manual calculation still needed nowadays in structural design?
5

Is manual calculation still needed nowadays in structural design?

Is manual calculation still needed nowadays in structural design?

(OP)
I have been working in construction and engineering field for many years. But I have not done any structural design or analysis extensively for at least 10 years although I would analyze structures very roughly or on concept level occasionally. When I was doing structural design many years ago, my manager didn't want to buy computers and software to complete designs. So I had to do everything manually. Fortunately, the company had a small library contained various standards, codes, engineering manuals, etc. I could always found the design data of various loads (wind load, live load for various structures, etc.), property for common material (weight, strength, elongation rate, proportion, etc.) and common structural calculation formulas. But I know that software are so powerful now. They can do almost all structural calculation for us and are much faster. Do we still need to master manual structural calculation skills?

RE: Is manual calculation still needed nowadays in structural design?

Yes, manual calculations are essential, IMO. However, it depends on what your definition of "manual calculation skills" is. For me, a "manual" calculation often involves entering formulas into MathCAD or Excel.



RE: Is manual calculation still needed nowadays in structural design?

Quote:

Do we still need to master manual structural calculation skills?

Absolutely. And just plugging and chugging on some spreadsheet/FEA software without thinking about the underlying assumptions is dangerous.

I personally do calculations (all the time) that there is no spreadsheet (that I am aware of) that can do it.

RE: Is manual calculation still needed nowadays in structural design?

Ditto, you will always need to be able to do your own calculations. First, I caution you, computer programs have flaws in them. They find out about the flaws by people doing their own calcs and comparing the results. I can easily give examples if I had to.

I also think you are referring to classical structural analysis (slope-deflection, 3 moment etc) as much as you are "calculator skills". You must have a good working knowledge of these to have an idea when your computer output is wrong. The programs are powerful and fast but they are also not responsible for your building falling down.

RE: Is manual calculation still needed nowadays in structural design?

Whenever I have to do something more than once, I make a spreadsheet for it.
First time use, it gets thoroughly double checked against manual calculations (even when the input is also based on manually inputting formulas/standard values/...).

RE: Is manual calculation still needed nowadays in structural design?

Most of my 'hand' calcs are based on a spreadsheet. That way I can change any variables I want to play around with the design. No reason to do a calc by pencil and paper anymore.

RE: Is manual calculation still needed nowadays in structural design?

(OP)
Thank you all for your valuable replies. When I say manual calc., it doesn't mean you use pencils, pens and paper. It means the classical methods, contrary to just enter the data into the computer, let the software do the all calculation and analysis. For classical calculations, you need to find data from authorized resources, such as reliable manuals, codes, standards, data publications, etc. Then choose the proper formula, then apply the results with the reliable resources to choose the size of steel bars, thickness of bearing walls, concrete, etc. The flaw for classical style is that different professionals may come to different conclusions. For example, some professionals may choose 1m x 1m column, the others may choose 0.8m x 0.8m column.

RE: Is manual calculation still needed nowadays in structural design?

That's not a flaw, it is a benefit. Why should we all be the same? It is called design for good reasons.

RE: Is manual calculation still needed nowadays in structural design?

Rational manual design often is often very satisfying.

RE: Is manual calculation still needed nowadays in structural design?

Slide rules are needed when the power goes out, so, yes, very yes to manual calculations.

Mike McCann, PE, SE (WA)


RE: Is manual calculation still needed nowadays in structural design?

On this subject a question. Can anyone point to a case or cases where computer calculations have resulted in some degree of damage claim against the engineer, faulting this use? Perhaps commenting on the lack of parallel manual checking calcs.

RE: Is manual calculation still needed nowadays in structural design?

I recently found a couple of quirks in my RISA model via rough hand calcs. Rather than fight with the program I reverted to hand calculating the various items I questioned. Wouldn't have caught the issue without hand calcs and hand calcs were the most efficient way to correct the issue.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)

RE: Is manual calculation still needed nowadays in structural design?

oldestguy,

I have been told that everyone today wants to see a diagram with pretty colours, such as is generated by FEA software. When I have done crash safety calculations, I have determined that my points of failure are bolts. Bolted connections are easily but incorrectly modeled by FEA. You really need to do your statics and your moments about a point of rotation.

I did a crash safety analysis on a system that sat on six anti-vibration mounts, three to a side. If each mount were rated at one sixth of the mass of the system, the crash moment would be resisted entirely by the two mounts at the far end. Statically, this is not good at all. Energetically, it probably will work (???). When I am in control of designs like this, there are four (only) correctly sized mounts.

--
JHG

RE: Is manual calculation still needed nowadays in structural design?

When a contractor that I worked for, slid girders over the electrified tracks in Bridgeport, CT, back in the late 1990's, a hired structural engineer from Brewster, NY did all the calculations, several pages long,by hand. His work took a few months to complete and the project was done at night without a glitch.

RE: Is manual calculation still needed nowadays in structural design?

See... The electricity went out and he had to do the calculations by hand.

I stand vindicated. thanks2

Mike McCann, PE, SE (WA)


RE: Is manual calculation still needed nowadays in structural design?

(OP)
'That's not a flaw, it is a benefit. Why should we all be the same? It is called design for good reasons.'
Kind of agreeing with you, hokie66, otherwise there might be no Leaning Tower of Pisa.

RE: Is manual calculation still needed nowadays in structural design?

I still do a lot of things by hand simply because it's faster - time is money!
Most wood and steel beams, joists, wind loads, seismic and sheer walls I typically do on my calculator.

RE: Is manual calculation still needed nowadays in structural design?

I transitioned from a large company to a small one. I previously had all the software I wanted all the way up to ANSYS (and I used it a lot). My new firm cannot afford software like that. I have an old version of STAAD to do my structural analysis, but I still have to do all my code checks by hand. I have been developing a lot of Excel spreadsheets since I have been at my new job.

Hand calcs are also good for spot checking things real quick.

RE: Is manual calculation still needed nowadays in structural design?

I have a solar powered calculator. Will work during daytime with the lights out.

RE: Is manual calculation still needed nowadays in structural design?

I can't imagine to work on complex projects by hand. The stuff architects draw nowadays... Good luck earning your salary without FEA. Or my projects are very different from yours.

RE: Is manual calculation still needed nowadays in structural design?

Some young engineers now use software without doing hand calculations first. They become data entry workers instead of engineers.

I personally find a software, use hand calcs to extensively check the results for a few months, and then use the software based on faith and common sense. Because if I don't use the software, I won't be able to keep up with my competitors.

RE: Is manual calculation still needed nowadays in structural design?

Seems the conversation has strayed some from the original post. To me the original post was "Do you need to master "manual structural analysis" when computer programs are so advanced". The original poster seams to have corrected "manual calculations" to "manual structural analysis".

With that in mind, you still need the manual structural analysis ability even with the best software. You may not have to "master it" but you had better be pretty capable of knowing it. With very little manual ability, you will not know when something just looks wrong.

Quote (Ron247)

First, I caution you, computer programs have flaws in them. They find out about the flaws by people doing their own calcs and comparing the results. I can easily give examples if I had to.

I will elaborate, on this previous quote. A well-known software to this forum I used about 30 years ago. It is a good software even now. But, we noticed the seismic reactions for seismic acting in a certain direction was wrong, seismic to the left, had reactions to the left for example. We contacted them, they found the problem and corrected it. Had we not been capable of noticing it, the software would have run several more days/weeks/months until someone else reported it. They released a new version because of this but never stated why the new version was released. I have come to find out, that is fairly standard in the industry. So anyone who did not notice the flaw, tough luck.

I fully understand that structures are extremely complicated in comparison to the "good ole days" but that does not diminish your need to at least have a feel for what looks "right".

RE: Is manual calculation still needed nowadays in structural design?

Oldestguy, the Sleipner A offshore platform is the usual cautionary tale about not understanding the computer model and not having effective checking.

Ron247, what software are you referring to? It's not industry standard to hide bug fixes. That's a sign of a shonky company. See the link below: warts and all.
http://spacegass.com/history/index.htm

RE: Is manual calculation still needed nowadays in structural design?

Sorry, I will not mention their name. They are a very well established company and their policies have most likely changed since the early 90s. So maybe a more correct statement by me is "It was a fairly common at the time". They have been mentioned multiple times in this forum. This was about 25 years ago, but I have found several more companies that send out updates but never really say why the update was released. They may say, "Corrected an input issue with Loads" but do not say "Any force that was input as Force in the Positive X was actually stored in Moment about the Negative Y". To elaborate on the problem, they assumed seismic in the X would be worked first, then seismic in the Y/Z. So after seismic X was worked, they cleared out the array and did Y or Z. I did my project Y/Z first, then X. They software had no requirements either way but all their examples were X, then Y/Z. Well, if you do Y or Z first, the array did not get cleared out, so your X information was added to your Y/Z information.

I have not worked with their software in about 25 years but do remember the release with the correction. The information never stated the precise problem. That is why I started looking more closely at releases, especially the ones with letters like 14b, 12a, 6d. The scheduled releases may be 12, 14, 19 etc but the lettered ones were generally repairs. I was just making a point that software has bugs and will continue to have them forever. I have done a lot of programming myself and know how hard it is to be foolproof. Even though I am from the Fortran days, basic programming concepts are the same.

RE: Is manual calculation still needed nowadays in structural design?

I agree you need fundamentals. Ability to check and validate results is a must. I quickly spot when something is wrong, but most of the time is something I modelled not software itself.

RE: Is manual calculation still needed nowadays in structural design?

I think the recent thread on shear deformations, in this forum, is relevant to this discussion.

Applying theoretical procedures in manual calculations can give incorrect results.
Examination of the results of simple computer calculations can give valuable insights.
Asking whether we should use computer calculations or hand calculations is false dichotomy.

Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/

RE: Is manual calculation still needed nowadays in structural design?

With most software going subscription, I am now doing most of my calculations by hand with my old HP 15 using classical methods. I still have a copy of Risa 3d that I "own" (for now) but I only use it for really indeterminent problems.
I get to build and test break all my stuff and that's where my final answer comes from.

RE: Is manual calculation still needed nowadays in structural design?

Same here Buggar, I still have my last purchased Risa 3D but due to subscriptions, I am free to look elsewhere each year. In the past, upgrades were less $$$ than purchasing someone else's product. I think I was with RISA since the mid to late 90s. I have a lot of spreadsheets and other routines to do the bulk of my work.

RE: Is manual calculation still needed nowadays in structural design?

In 20 years, I've found very few errors in commercial software, but there have been numerous examples of programs performing a calculation in a way that I don't agree with. For that reason, I always check a new (or new to me) feature with manual calculations before I trust it. I think it's malpractice to not do this.

RE: Is manual calculation still needed nowadays in structural design?

Quote:

In 20 years, I've found very few errors in commercial software, but there have been numerous examples of programs performing a calculation in a way that I don't agree with. For that reason, I always check a new (or new to me) feature with manual calculations before I trust it. I think it's malpractice to not do this.

All calculations should be checked, but why does the check need to be a "manual calculation"?

Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/

RE: Is manual calculation still needed nowadays in structural design?

I try to simplify things so that I can run some quick hand calcs on the important parts. Usually I am trying to get a modeler/drafter started long before the final member sizes are chosen and details are complete. Complicated items get the complicated computed models.

If done properly, hand calcs tell the story about the design intent of the structure. Maybe 50% words and 50% numbers. Young guys who eschew hand calcs produce all numbers and tend to neglect the telling of the story. Kudos to those who do it all!

As structural engineers, our job is to tell the contractors what the Owner wants to build, it's not to produce volumes of calculations (unless your AHJ requires it!).

RE: Is manual calculation still needed nowadays in structural design?

OK, but you said that not to do the check by manual calculations was "malpractice".

Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/

RE: Is manual calculation still needed nowadays in structural design?

Quote (IDS)

All calculations should be checked, but why does the check need to be a "manual calculation"?

Agreed. I believe we're using the term "manual calculation" to mean a bunch of different ways to check software output and it was the original question.

I regularly check software or my spreadsheets against each other. Probably the most beneficial checks I've found are to benchmark software against some textbook examples. This establishes that the software does what you expect it to do and verifies the methods. These checks are generally quick to do but valuable, especially when learning new software.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)

RE: Is manual calculation still needed nowadays in structural design?

Quote:

All calculations should be checked, but why does the check need to be a 'manual calculation'?

Good question. IMO, one way or the other, the verification must be grounded in the engineer's knowledge. That usually means manual calculations, comparison with another program the engineer wrote or verified, or a textbook example that the engineer understands.

RE: Is manual calculation still needed nowadays in structural design?

Hi,

Your hands Calc are kind of Backup and part of the verification process.
even if it's too complicated, you should be able to simplify the problem and check with your Hands Calc if you are right.

Best,
Mohamed

RE: Is manual calculation still needed nowadays in structural design?

I am seeing great replies.

Personally I like using Mathcad for manual calculation as well. It is much easier to go back and understand weeks later than Excel, and it is easy to update number when the architect or your project engineer change their mind.

RE: Is manual calculation still needed nowadays in structural design?

“Do we still need to master manual structural calculation skills?”

I am just now seeing this post – and it is a topic near and dear to my heart.

YES! In my opinion all computer analysis must be validated with simple manual calculations. To blindly rely on software is, in my opinion, negligent. If nothing else, a few minutes spent validating your computer analysis with a calculation or two gives you some “simmer time” – time to stare at the computer results and ask yourself, “Does this make sense?” The blind reliance by on computers by some engineers is in my opinion, a disaster waiting to happen. I have been a structural engineer for over 40 years and I have seen several “near misses” because of engineers having the mindset “…but the computer said it was ok.” In addition, engineers must always ask themselves, “What did the computer not check?” What are the flaws in the software? What are the default settings? Are you even aware of all of the default settings?

Manually validating the results of software analysis and design is something that is not taught is schools - but it should. Young engineers graduating today seem to be proficient in jockeying the software, but if you ask them if the answer makes sense, they usually give you a blank look.

RE: Is manual calculation still needed nowadays in structural design?

In response to “oldestguys” question asking if any errors have resulted due to mistakes by the computer which resulted in the EOR being held accountable – I am certain that there have been such claims against engineers. The problem however is that design flaws are often discovered during construction. A flaw is found. The reason for the flaw is determined. A fix is implemented. The structure is made safe. Someone is blamed – and that entity pays for the fix (or their insurance company pays) – and if no one is injured, the public never finds out about the original mistake. I suspect that often “computer errors” are the result of young engineers with little experience being given the task of modeling complex structures without having a full understanding of what they are doing. So it is not necessarily a flaw with the computer, but is instead a flaw in understanding what the computer is doing – and a failure to manually validate the results.

RE: Is manual calculation still needed nowadays in structural design?

Quote:

To blindly rely on software is, in my opinion, negligent.

I'm pretty sure that no-one is suggesting that we should blindly rely on software. The question is, is manual calculation the only valid method of verification? I don't think it is.

The blind reliance on books by some engineers is in my opinion, a disaster waiting to happen. I have been a structural engineer for over 40 years and I have seen several real failures because of engineers having the mindset “…but the books said it was ok.” In addition, engineers must always ask themselves, “What did the calculation not check?” What are the flaws in the text? What are the unstated assumptions? Are you even aware of all of the unstated assumptions?

Validating the results of software analysis and design with alternative and independent computer analyses is something that is not taught in schools - but it should. Old engineers who graduated long ago seem to be proficient in jockeying the manual calculations, but if you ask them if the underlying assumptions and simplifications might be better checked with a computer analysis, they usually give you a blank look.

Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/

RE: Is manual calculation still needed nowadays in structural design?

Quote (IDS)

The blind reliance on books by some engineers..

Quote (cliff234)

To blindly rely on software is,...

As someone who has only been a structural engineer for 12 years I can admit to having fallen into both these categories on occasion, some early in my career some later. I've reached a point now where I have enough experience that I can approach things trying to have any idea of what the results should be, not necessarily always by the numbers I start simple with shapes of shear, moment, and deflection diagrams which I've found to be the quickest indicators of an incorrect analysis or assumption in the model, or at times my own misunderstanding of the behavior. If it is an analysis type I'm not fully grasping I run it in multiple software packages, try to find multiple text references, discuss my hang up or misunderstanding with my seniors, and when I'm really stuck I post here.

Quote (IDS)

In addition, engineers must always ask themselves, “What did the calculation not check?” What are the flaws in the text? What are the unstated assumptions? Are you even aware of all of the unstated assumptions?

Quote (cliff234)

..“Does this make sense?” ...“What did the computer not check?” What are the flaws in the software? What are the default settings? Are you even aware of all of the default settings?...

I think this is some great combined advice, it's not always about the computer not checking something perhaps you knew it did not check something but you did not know that it was a required check for calculation. It's the garbage in garbage out saying.

I would add onto IDS' list with "Do I know what this check is for?","Should I ask for help interpreting these results?"

I've found throughout my career that asking for help for fear of feeling like an idiot is a hurdle everyone has trouble jumping over.





Open Source Structural Applications: https://github.com/buddyd16/Structural-Engineering

RE: Is manual calculation still needed nowadays in structural design?

From the original post

Quote (ccpe)

But I know that software are so powerful now. They can do almost all structural calculation for us and are much faster. Do we still need to master manual structural calculation skills?

It still seems to me the question is can we solely rely on a computer that has some powerful structural analysis software? My answer is no we cannot and most likely will never be able to. Too many factors involved for the project to go off without a hitch. We all need to question computer output to some degree, not blindly accept it.
  • Program has glitch no one ever noticed
  • Program is correct but my input is wrong (face it, we all make that mistake at least once a month)
  • The less skilled you are at the classical methods, the more prone you are to accept erroneous output
  • The less experienced you are, the more prone you are to miss that the output looks erroneous
  • Other
The way we "question" the output can be done in multiple ways, we can do hand calcs, use a spreadsheet, use Mathcad etc. but as already stated, we need to take a breather and review any output regardless of how powerful software can be. The talents and tools we use to review it are going to be different for all of us.

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