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rodsika

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http://www.personal.psu.edu/kar5230/blogs/kyles_professional_portfolio/How%20to%20Design%20a%20Singly%20Reinforced%20Concrete%20Beam.pdf [Broken]

I'm stuck with a formula above. It says that to calculate for Moment of a beam... use the formula

Mu= w L^2 / 8

now given w = 1000 lb/ft, L=20 feet... then Mu= w L^2/8 = 1000(20)^2/8 = 50,000 lb-ft

(although it's written as 500,000 lb-ft in the site.. i think it's wrong?)

Anyway. my question is.. i have spent half a day doing conversion from lb-ft to Kilonewton-meter and I can't seem to get it right.

I found out the following formula for converting between the two units:

1 kN - m = 737.56 ft-lb

1 kN/m = 68.52 lb/ft

Now in the above example given w = 1000 lb/ft, L=20 feet

1000 lb/ft = (14.59 kn/m x 6^2) / 2 = 525 kn-m/8 = 65.65 Kn-m

Now converting Kn-m to ft-lb...

65.65 KN-m x 737.56 ft-lbs / 1 KN-m = 48424 ft-lb or (lb-ft I assume this is the same).

Now why can't it be equal to the 50,000 lb-ft in earlier calculation??

I'm stuck with a formula above. It says that to calculate for Moment of a beam... use the formula

Mu= w L^2 / 8

now given w = 1000 lb/ft, L=20 feet... then Mu= w L^2/8 = 1000(20)^2/8 = 50,000 lb-ft

(although it's written as 500,000 lb-ft in the site.. i think it's wrong?)

Anyway. my question is.. i have spent half a day doing conversion from lb-ft to Kilonewton-meter and I can't seem to get it right.

I found out the following formula for converting between the two units:

1 kN - m = 737.56 ft-lb

1 kN/m = 68.52 lb/ft

Now in the above example given w = 1000 lb/ft, L=20 feet

1000 lb/ft = (14.59 kn/m x 6^2) / 2 = 525 kn-m/8 = 65.65 Kn-m

Now converting Kn-m to ft-lb...

65.65 KN-m x 737.56 ft-lbs / 1 KN-m = 48424 ft-lb or (lb-ft I assume this is the same).

Now why can't it be equal to the 50,000 lb-ft in earlier calculation??

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