Solution to Problem 504 | Flexure Formula

Problem 504
A simply supported beam, 2 in wide by 4 in high and 12 ft long is subjected to a concentrated load of 2000 lb at a point 3 ft from one of the supports. Determine the maximum fiber stress and the stress in a fiber located 0.5 in from the top of the beam at midspan.

Solution 504



When putting values in formula
4500 - max moment ->ok
2 - half depth -> ok
2*(43)/12 - moment of inertia -> ok
but what is the 12 above line?
can u help me?

Conversion of lb-ft to lb-in.

Actually they have just converted the unit of the moment from lb-ft to lb-in by multiplying 12 because other parameters are in inch and as you know 1 ft=12 inch so 4500 lb-ft=4500*12 lb-inch.

Hello. How did they get the 6 in M/6 = 4500/9 ?

That is by ratio and proportion from the moment diagram. Mm is at the midspan, or 6 ft to R2.

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