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
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why should we use excel 6
- Thread starter MALY
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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
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
GregLocock
Automotive
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
Cheers
Greg Locock
Chichuck:
The following site provide sample for your application as follow:
a- Check problem # 198 on Civil & Mechanical Eng Section
b- Sample with Drawing Modification Capability:
I hope this help.
The following site provide sample for your application as follow:
a- Check problem # 198 on Civil & Mechanical Eng Section
b- Sample with Drawing Modification Capability:
I hope this help.
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
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
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
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
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.
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.
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
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
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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.
GregLocock
Automotive
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
I beg to differ.
Cheers
Greg Locock
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
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
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.
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.
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Hi
If you are doing structural Calcs why not use something like Interactive Roark's Formulas 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
If you are doing structural Calcs why not use something like Interactive Roark's Formulas 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
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
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.
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GregLocock
Automotive
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
Cheers
Greg Locock
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