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Grade Slab Design.mcdx

sshastry
Regular Member

Grade Slab Design.mcdx

Hi

Attached is an mcdx file. I have an issue with the units. I'm expecting the units for fctm to be in MPa. But Mathcad does not seem to be in agreement. If I remove the 2/3 from the equation then the units are OK. Kindly help.

Sriprakash

5 REPLIES 5

Re: Grade Slab Design.mcdx

Hi,

The coefficient 0.3 is dimensionless? otherwise:

coeff.jpg

Re: Grade Slab Design.mcdx

It's better to start such questions in this forum as a discussion, rather than a s a document.

Anyway. You raise an expression (0.8 * fcu) to the power 2/3 where fcu has units MPa, and 0.8 has no unit.

Then you MUST expect the unit of the result to be MPa to the power 2/3.

Is it certain that 0.8 has no unit? If it had the unit of SquareRoot(MPa) then you would get MPa as a result.

Luc

Re: Grade Slab Design.mcdx

Here is another way to deal with an older unit-less formula where you are told "enter the compressive strength in MPa and you get the tensile strength in MPa".

You strip the units of the input values by dividing through the proper given unit and add the correct result unit at the end.

Not the way one should work in Mathcad, though, but its often not that easy to make a formula unit-aware..

Re: Grade Slab Design.mcdx

Luc

Many thanks for the response. I didn't know if I could attach files in a discussion. Anyway next time Ill start a discussion instead. Anyway, in my equation both 0.8 and 0.3 are constants with no units. Looks like I don't have any other choice than the work around suggested by you.

Thanks

Sriprakash

Re: Grade Slab Design.mcdx

Oh, you do have another choice.

If the expression you are using is derived emprirically, then rather than to attach a unit to 0.8, I think it's better to remove the unit from fcu inside the power and afterwards re-attach it to the result, as Werner has shown.

And, yes you can attach files to a discussion item, either by choosing the 'advanced editor', or by 'Actions'-> 'Edit'-ing the discussion after a first submission. In both cases you will find an 'Attach' button in the lower left corner of the editing window.

Success!
Luc

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