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why should we use excel
6

why should we use excel

why should we use excel

(OP)
I would like to ask all of you who use excel as your spreadsheet for designing, how would u rate excel for structural calc.? and how i can start? is there any book would u recommend? i've been using mathcad and tedd's, but i have many excel applications i used as well, excel seems easy but doesn't check units as the other programs i use, please help
Replies continue below

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RE: why should we use excel

I share your concerns. Since it would be easy to include logic that gives the wrong answer for just a small range of inputs it seems to me that you could not pick up a third party sheet and use it for any mission critical calculations.

On the other hand, everyone has a copy and it is a great tool.

Cheers

Greg Locock

RE: why should we use excel

My 2 cents:

For designing and structural calculations, I prefer NOT to use Excel, primarily because the formulas are hidden within the cells, logic paths are hard to follow if the program has to branch several times, there are limited functions available so you have to build your own and debugging is a pain in the rear.

I prefer to use MathCad, where the formulas are visible and "live", editing and debugging chores are easier and there are an enormous breadth of built-in functions to choose from.

I have heard that Mathematica is in the same class as MathCad.

MathCad also produces excellent ouptut that is easier for others to review and understand.

RE: why should we use excel

Oh yes - you can use units in MathCad - a HUGE benefit, especially in the debugging stage.

RE: why should we use excel

Excel has many useful capabilities especially with table and form templates that made easy some calculations. However, is very limited for other complex calculations or engineering report.

Mathcad allow users to dynamically link a data source from Excel worksheet with application files.  This capability to combine the good features of Excel makes Mathcad very powerful for many engineering application.

RE: why should we use excel

Not only can you include units in Mathcad, but you can also do unit conversion on the fly.  Onve you've calculated a quantity, it's trivial to get the answer in another unit system.

The only really annoying thing is that Mathcad's plotting capabilities are still pretty much in the Stone Age, with the exception that the 3-D plots can be manipulated live.

TTFN

RE: why should we use excel

(OP)
Thanks guys, I have the same feelings, I like excel but it is scary to use it sometimes

RE: why should we use excel

If anything, it should be less scary than Mathcad.  

There are easily 10 times more people beta-testing, oops, I meant using, Excel than Mathcad.  

This makes Excel much more likely to work correctly.  It's sad, but true.

TTFN

RE: why should we use excel

I'm not a regular Mathcad user, I've been working with Excel for a number of years.  I tried Mathcad, and I'm more comfortable with Excel, for the following reasons:

1) it does works with tables better, in structures, I use many tables, many more than nice, closed form equations.

2) I can do a good job of getting error messages, notes and the like to appear or not appear using some if tests with text and "" values in them.  To me this is very important for an engineering calculation.  I can't do this very well in Mathcad.

3) Since I work in the US, units are not a big problem for me, I usually work in imperial units.  When I do try and use a metric or SI unit, I can often do that merely with some if tests as well.  Not pretty, not elegant but it works.

4)  I don't have much trouble with equations being buried in cells.  I tend to not use a lot of branches in spreadsheets, I prefer to use a lot of if tests, so those branches that were mentioned don't occur.  Another thing I do is use labels in cells to display the equations I'm using, so a user or a checker can see them.  


Regards,

chichuck

RE: why should we use excel

While I agree that Excel is a great tool, from the perspective of producing output that a customer (or another engineer) can read and understand, MathCad suits me better.  I also find that when I go back to an Excel spreadsheet that I have not dealt with for 6 months, it takes more time to visualize the methodology than from an old MathCad document.

RE: why should we use excel

MALY,

Interesting thread. I use MS Excel and MathWork's MATLAB for most "programming" type problems. These two packages share the limitation of visualizing the formulas like MathCAD can. It is a bit clumsy, also type the formula out as best I can in the cells adjacent to the adjacent cell for a bit more clarity in excel.

One question, though, what is "tedd's" that you refer to in your initial post.

Best regards,

Matthew Ian Loew

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: why should we use excel

Anyone who is looking for a free alternative to Matlab is well advised to check out Scilab, which has been ported to Windows. I think that scilab is actually easier to use than Matlab, but have no experience in running large or complex calculations in it. Some of the demos are amazing. http://www.scilab.org/

My take on Excel is that it is fine for designing stuff iteratively, but the final answer needs to be validated by some other means, except in the most trivial case.  

 

Cheers

Greg Locock

RE: why should we use excel

(OP)
Tedd's is spreadsheet program using MS word, it is adds on to word , it is very good , you can check it at www.tedds.com

RE: why should we use excel

I wonder, how would all of you do the following in Mathcad:  

when calculating wind loads on a building or structure, using ASCE 7-98 or 7-02, part of the process involves pulling numbers out of the table in Figure 6-6.  It involves reading numbers in a table, and interpolating them.  No equations are given, only the table values.  

I can do this, abeit a bit awkwardly in Excel.  How would you read this table in Mathcad, then interpolate between the lines and columns of numbers in the table?   

Part of the table is reproduced here:

Values of External pressure coefficients, Cp

                   Theta

h/L  |   10    15    20    25    30    35  45 60
-----+---------------------------------------------
0    |  -0.7  -0.5  -0.3  -0.2  -0.2    0   0  0
0.25 |  -0.7  -0.5  -0.3  -0.2    -0.2    0   0  0
0.5  |  -0.9  -0.7  -0.4  -0.3    -0.2  -0.2  0  0
1    |  -1.04 -1.0  -0.7  -0.5    -0.3  -0.2  0  0



Regards,

chichuck

RE: why should we use excel

Somewhat similarly.  In Excel, there are lookup functions that you would use to find the closest value.

Mathcad has a similar approach, with the exception that you can then use the table to interpolate between values.  There is a sample sheet for the ASCE wind load calculation somewhere, but I haven't been able to locate it.

TTFN

RE: why should we use excel

IRStuff,

But I'm not looking for the closest value, I want to interpolate between table values, say for h/L = 0.33 and theta = 22 degrees.  

This I am able to do in Excel, but awkwardly, as I said.

What functions in Mathcad are you talking about that would be used to interpolate between the table values for h/L = 0.33 and theta = 22 degrees?  

chichuck

RE: why should we use excel

Mathcad has 2 built-in interpolation functions, interp and linterp.  

Linterp is the linear interpolation.

Interp uses a vector generated by any of 3 spline functions, lspline, pspline, cspline.  They're all essentially the same, except for how they deal with endpoints, e.g., linear, parabolic or cubic.

If you search the Mathcad Collab at http://collab.mathsoft.com/~Mathcad2000
there was a discussion in the last 6 months on how to do a 2-D interpolation as well, but it's essentially running the spline fit in 2 dimensions.

TTFN

RE: why should we use excel

Check in MathCad Resource Center on Data Analysis the example for Two-Dimensional Spline Interpolation example.

With some modifications you should be able to do the work.

Good Luck

RE: why should we use excel

In addition to "hiding" formulas, one other "security" issue arises with Excel.

If you keep a spreadsheet under your own control, then it is just a programmable calculator.

If everyone has their own copy of the spreadsheet or access to the original (shudder,) you are never quite sure that someone hasn't gone beyond altering the inputs (OK) to altering the formulas (maybe NOT OK.) And it is cumbersome at best to "audit" a spreadsheet to find out whether it is still valid.

The upshot? Fine as a scratchpad, but for any work which must be traceable or verifiable, don't use a spreadsheet, it is a lawsuit waiting to happen.

Ron

RE: why should we use excel

IRstuff & cuky2000,  linter looks like the trick.  I'll try that.  Thanks a lot.

Paron,  I have a couple of thoughts on your remarks.  First, it is possible to lock an excel worksheet so it cannot be changed, and protect that lock with a password.  You can selectively unlock cells where input data will go.  I've gotten spreadsheets that are like this off of the web. It seems like a good way to solve the problems you mention.  Second, it seems to me that all those same issues will be present with a Mathcad file.  You weren't trying to suggest otherwise were you?  


regards,

chichuck

RE: why should we use excel

all,

I've been reading this thread and have still more thoughts.  The issue of units was reaised earlier.  I'm trying to work up a Mathcad worksheet to calculate wind loads on a building using ASCE 7-02.  I'm finding this about units in Mathcad.

1) Most of my input for this is in length units, and one item is velocity.  I have to collect all my input and put it into one section of the worksheet.  This is not a problem.  

2)  One of the inputs is a table of specific height values for which wind pressures will be calculated.  This is numbers put into a matrix with 1row X 15 cols.  I've multiplied this by the units ft in English units.  There are several places where I put these numbers into other matricies, always so I can output a table of values.  Whereever I do this, I have to first divide by the units, because I can't put numbers with units attached into a matrix, there can only be "bare" numbers.  So, if I change to metric input, its easy to change the units on the input table, but for those places where the numbers must be stripped of units, then I'm wrong until I go somewhere else and change the divide by units before using bare numbers.  

3) there is one critical number, a constant that is used in the calculation, it is a multiplier that has the value .00256 in English units, and 0.618 if using metric.  I don't want to have to input this number, the worksheet should be able to use the correct number.  For this case, I can set a veriable called "unitsflag" to English or Metric, and then select the proper constant.  

4) one of my tables has text placed over the top, with text displaying column headings and units.  These need to change depending on english or metric.  I'm going to try the units flag on this one too, I don't know if the text spacing and formatting will carry through though.

Maybe the units flag can be extended to all the other units as well, for example, depending on the "unitsflag" value, then "units1" = 1*ft or 1*m,  "units2" = 1*mph or 1*m/sec, "units3" = 1*psf or 1*N/m^2.    But that means a lot of units that are showing up as unit1, unit2 or unit3.  Then I still have to go to output values and manually type in the correct english or metric units.  

So, its starting to look like the units are as hard with Mathcad as it is with Excel.  

Anyone else have ideas about the above?

regards,


chichuck

RE: why should we use excel

Up until recently Mathcad was transparent, that is, the only calculations that took place were the visible ones. Recently IRstuff helped uncover a bug where this is no longer quite true. If you have to check a mathCad sheet make sure that all regions are separated and maximised to avoid this.

Cheers

Greg Locock

RE: why should we use excel

cuky2000

I've seen both of those.  The first one is dated, it uses ASCE 7-95, I'm working on one using ASCE 7-02.  They are different.  This one also has the same problems I've been talking about:  there are many places all over that worksheet that have units that have to be changed from english to metric if I want to make that change.  Not just input numbers, but output and intermediate calculated values as well.  

My point is, yes, its easy to just go in and change the units on an output value from ft to m, but that doesn't work on a wind load calculation, since there are many intermediate values that have to be changed as well, even some of the "constants" in the code, eg gradient height, critical hill height (used for calculating Kzt) and that all important coefficient .000256 used in calculating Kz must be changed for metric.  Just changing the units on the last output values in this type of calcuation will actually end up making the answers wrong.  

I also noted that I had trouble changing from lb/m^2 to N/m^2.  That's doesn't seem to be a direct change, I think maybe the lb is actually a lbm, not an lbf.  


Another example of this is any calculation you might do for concrete.  Look into ACI 318.  There are many places where they have "constants" that actually have units attached to them.  When you switch from english to metric for those, not only do you have to concern yourself with retyping the units themselves, but for those "constants" the values change as well when you go from english to metric.  


I'm saying that its as hard to change unit systems here in Mathcad as it is in Excel.  

chichuck

RE: why should we use excel

When you use Mathcad with any unit system, the internal constants with units do NOT need to be changed.  

200 W/m-K will work in the equation whether you use ft, inches, or furlongs as the dimension of the object.

The problem is that most people stick a value into the equation and then "fix" the units after the calculation.  This is the way you'd do it in Excel, since it can't take units at all.

Once you set up the equation in the correct form with ALL constants inserted with correct units, you can change units on any or all inputs as desired.  This is what makes Mathcad substantially more useful than Excel for these types of calculations.

As for the lb/m^2 question, the correct unit in Mathcad is lbf - pounds force.  lb is pounds mass, which coverts to 2.2 kg of mass.

TTFN

RE: why should we use excel

I have found that "constants" can often be researched to determine the original units, ie - what it was converting from/to.  Then, I put it in MathCAD with the appropriate units.

For instance, the 0.00256 in wind pressure calculations is the density of air divided by the acceleration of gravity expressed in psf.  In MathCAD then, you would not use 0.0256 but change the equation to Pressure:= Velocity squared X DensityAir / g.  This assumes that you have defined DensityAir in whatever units you choose.

Using this new equation, you can select the output units explicitly at the equation or by changing the Default Units.

If units are not known and can not be found, I put the equations in without units but add a made up unit to multiply the result by.  Example:
Vmph:=1*mph (define a new unit)
Pressure:=.00256*V^2*Vmph (calculation)
Pressure= (show the result)

The equation result will display in the default units (SI / MKS / English, etc.).  Changing the default units will change all equation results.

RE: why should we use excel

You don't even need to change the default unit system to get different results.  I always leave my sheets in SI units.  When you ask for pressure, Mathcad responds in the default N/m^2, but the expression for the answer has a placeholder for putting other units such as psi, pascal, lbf/ft^2, etc.  

It's absurdly simple; so simple that if you mistype or otherwise get the unit wrong, Mathcad's display will show up with extraneous units to let you know that you got something wrong.

TTFN

RE: why should we use excel

IRStuff -
I try to leave all results in the default units so I can make SI or English documents for different clients without paging through and revisiting the placeholder after each result.

If only there were user defined unit systems!!

RE: why should we use excel

It is possible to get the best out of both worlds by linking Mathcad with excel using a fairly simple VBA subroutine which reads and writes arrays of data between the two programmes.  The syntax is in the mathcad help files.

RE: why should we use excel

2
The arguments in favour of MathCad are, in my opinion, misplaced. The reliance on MathCad to provide units so that the user thinks that the answer must be correct, without checking, is a danger. An excample I have is in calculating frequencies using standard formulae. The units I used were all correct as far as I was concerned, ie. Kg, Newtons and mm, and MathCad dutifully provided the answer in Hz, as I expected. Sadly MathCad is not that bright and the answers were wrong by a constant factor of 31.6. Whether you use Excel or any other spreadsheet, don't expect them to do the thinking for you.

RE: why should we use excel

So are you saying that the less help the program gives you in identifying problems, the better it is?

I beg to differ.

Cheers

Greg Locock

RE: why should we use excel

How does giving "false" results help?

RE: why should we use excel

It's not a question of false results, but whether you want to spend $150/hr of customer time figuring units every single time on every single calculation or be smart enough to pick up on the occasional mistake.

My money is on getting some clue from the unit conversion errors, rather than getting only 15 digits of erroneous floating point from Excel and the nhave to backtrack to find the error.

TTFN

RE: why should we use excel

There is something to be said for going through the effort of setting up the spreadsheet manually.  Total control, and all errors are locatable.

RE: why should we use excel

Most complex calculations are common equations. It is my opinion that these equations should be inputed and checked once and then be in some sort of accessible library.

In excel this would be in the form of writing user defined functions. For excel these equations may be units dependent, but it is easy enough to have two equations one for  english and one for si named xxxxxxen and xxxxxxsi. Writing functions also requires variable names rather than cell addresses which makes checking the equation easier with meaningful names.

I know mathcad has function libraries although I have not had much access to use mathcad.

Mathcad you can put whatever units in and you'll get correct numbers out. For excel have your functions use common industry units. A soil permeability going into an equation is going to be in cm/s with site dimensions in m and coming out may be a flow in m^3/s. In the excel function the conversions can be plainly stated separate from other calculations. Have a list of equations with inputs outputs and the forms of both.

Everything that is not a common equation most likely has simple units. All of which should be checked anyways and should be simple to make sure they are correct units.

RE: why should we use excel

Hi
If you are doing structural Calcs why not use something like Interactive Roark's Formulas www.roarksformulas.com All the work is done for you and you still have a tool like TK Solver to solve backwards and forwards or build your own Math models.
PS It links to Excel with ExcelLink

RE: why should we use excel

I forgot anyone who wants to get TK 4 for nothing all they have to do is place a banner on thier site. UTS offers this through the links for TK program
http://www.uts.com/free_software2.html

RE: why should we use excel

Look out side of the box!  Excel is not the only spreadsheet program.  What are you all married to Bill Gates?  Try some others.  They have more accurate calcs and better graphing, and in general are much more versatile. To top it of, the bonus is most of them will import and export excel files directly.

RE: why should we use excel

Shyhigh,
my "box" has Excel loaded. All workstations in our plant ( hundreds of them ) have Excel loaded. That's why we use it. We do not need to verify if a file opens or not on another PC. It is simple like this.
gearguru

RE: why should we use excel

Exactly. I would like to use, say Open Office, so that I can use the same software at home as at work. But, how can I be sure that OO makes the same calculation as Excel? If I use OO and the corporate standard is Excel, then I would be negligent at best if the answers were different.

Cheers

Greg Locock

RE: why should we use excel

Excel is the best spreadsheet program available, and I thank Microsoft for dominating the office software market, bringing a standard to the wide range of users. The other spreadsheets convert Excel ALMOST right, occasionally this almost brings the structures down.

RE: why should we use excel

Skyhigh, I am very interested in what you are saying.  Please give a couple of DETAILED examples of Excel's inaccuracies.

RE: why should we use excel

=MOD(12.3,(12.3/10))

also the stats have a bad rep (with people who sell alternatives)

Cheers

Greg Locock

RE: why should we use excel

Greglocock,
Thanks for the pointer to scilab.  I love it! and also the nice thing about is, it runs under MS windows and Linux.  Try OO is is a well structured program, also SMS Star office but only v6.0.  Also look at Xandros for an OS or Lindows if you like windows drivers.

RE: why should we use excel

OO is the new name for the Star Office. It is not anymore maintained by SUN. I experienced some problems with it trying to open some Excel created *.xls files, the graphs did not show properly.
For obvious reasons I use it only at home, for my private stuff.
gearguru

RE: why should we use excel

Skyhigh / GregLocock

I can't access scilab.org

I get error message: forbidden access. Why?

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