Soil Pressure - U.S. to Metric Coversion Question 3

[rscott]

Hello, I hope I have found the right forum.

I have a project that requires addition of metric values to a set of standards now shown in U.S. only (they will now show dual units).

I am not an engineer, but have construction and technical background.

I am somewhat confused as to the proper conversion (standard useage) for the U.S. designation of Pounds Per Squre Foot(PSF)to metric.

Is the normal conversion factor:
square meter (kg/sq m)
{note I could not show supersubscript 2 to define "squared)

Or would Pascal be appropriate? (I am not certain if Pascal is a square/unit measurement or just pressure).

If Pascal is a square/unit measurement, would either of the two be appropriate?

I hope I laid this out so it is not confusing.

 

[austim]

rscott,

Pascal is NOT the right measure for soil pressure, since 1 Pascal is such a low pressure. You can think of it as the weight of 1 'standard' apple (the Newton being the unit of force)on every square metre.

The usual geotechnical pressure unit is kilopascal. The rate of conversion is 1 kPa = 20.885 lbs/sq.ft.

 

[rscott]

Perfect...

Right, kilopascals it is, I should have been clearer on that point.

I just wanted to make sure the conversion factor was acceptable.

i.e 2700 psf = 129.28 KPa.

Thanks so much!!

 

[DRC1]

Ingersoll Rand sells a book "Cameron Hydraulic Data" which has the best conversion information I have seen. If you are doing a lot of converting it will prove very useful

 

[BigH]

As originally American, I loved the English system - for you seldom lost decimals. Moving to Canada and now working overseas, they all love the metric (or SI - system internationale) but, you know, even thought kPa ought to be used for pressure (MPa for concrete and rock strengths), our contract documents are all over the place:

N/mm2 (= kPa)
kg/cm2
ton/cm2

etc. Then there is the "force" vs the "mass" pressures. Generally, all these differ by some factor of 10 or 100 but it is crazy to have to always have to remember which. Insist on kPa; MPa. For unit weights, use kN/m3, not g/cc or kg/m3.

Best regards

 

[austim]

Hi, BigH,

N/mm2 is actually MPa. And for any dynamic calculations, we still have to consider mass as well as weight, so kg/m3 will have to stay in our vocabulary, like it or not.

 

[BigH]

austim:
See what I mean? I have MPa written down somewhere - but it is always a pain to have to find my little crib sheets!! May in dynamic calculations it is easier to use kg/m3 (although, I suppose you could use kN/m3*.981 (or is that /.981??). But for soil weights for stability calcs, settlements, etc., kN/m3 is best!!
By the way - the CRC Chemistry handbook has a great listing of really wierd conversions besides common ones!
Take care - best regards.