Lb/f to kn/m and not consistent

  • Context: Undergrad 
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Discussion Overview

The discussion revolves around the conversion of units from pounds per foot (lb/f) to kilonewtons per meter (kN/m) in the context of calculating the weight of a beam made of concrete. Participants explore the discrepancies in their calculations and the implications of unit conversions.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant presents a calculation for the weight of a beam in both metric and imperial units, noting a discrepancy in the conversion results.
  • Another participant points out a potential error in the width measurement used in the calculations, suggesting it may contribute to the discrepancy.
  • A third participant challenges the accuracy of the meter to feet conversions provided, asserting that the conversions are incorrect.
  • The original poster acknowledges an error in their calculations related to the dimensions used in their Excel formula.

Areas of Agreement / Disagreement

Participants have identified discrepancies in calculations and unit conversions, but there is no consensus on the correct conversions or the source of the errors. Multiple competing views on the accuracy of the conversions remain unresolved.

Contextual Notes

Limitations include potential inaccuracies in unit conversion factors and the reliance on specific measurements that may not be universally accepted.

violt
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I'm trying to convert lb/f to kn/m.
A concrete has weight of 23.54 kiloNewton/cubic meter which is equal to 150 pounds per cubic feet.

For a beam with the following dimensions
width = 0.3m = 0.84 feet
depth = 0.5m = 1.9685 feet

for the beam weight per meter in metric, it is 23.54*0.3*0.5=3.531 kn/m
for the beam weight per foot in english, it is 150*0.98*1.96=290.62 lb/foot

But if I convert 290.62 lb/foot to kn/m. I don't get 3.531kn/m but 4.240181 kn/m
here's the calculation

290.62 lb/f * 3.28 f/m * 1kn/224.8lb = 4.24 kn/m

why not 3.531 kn/m??

Note this is not a homework. Thanks.
 
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I didn't check the calculation, but I noticed you wrote 0.84 feet for the width but used 0.98 feet in a calculation a few lines down. Maybe that is where the error lies?
 
I don't know where you got your meter and feet conversions from, but they are in error.

1 meter = 39.37 in. = 3.2808 ft.

1 foot = .305 m
 
i got the error. It's formula in my excel which uses 0.6m instead of 0.5m. Anyway, thanks
 

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