|Sep25-12, 06:23 AM||#1|
Mu of a Beam
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??
|Sep25-12, 06:49 AM||#2|
20 feet = 6.096 meters, not 6.
|Sep25-12, 07:31 AM||#3|
|Sep28-12, 09:27 PM||#4|
Mu of a Beam
I'm trying to determine the deflection of the above beam. An engineer told me that deflections of beams from 6 meter to 7 meter is non-linear and high that is why many in constructions limit beam span to 6 meters for economy. What do you think of this. Anyway. Let's prove it by formula/calculations. On the following page is online calculator to solve for deflection.
Supposed span of beam is 6 meters, w of beam is 4.23 Kn/m, distance of deflection measured is at middle, Modulus of Elasticity is 57000x sqrt (fc=21) or 261206, what is the formula or how do you determine the Moment of Inertia so I can input it to the online calculator above, thanks?
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