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calculating moment capacity and section modulus for pipescy
calculating moment capacity and section modulus for pipes/cy
the awwa m11 gives section modulus = i/c = π * r^2 * t however, i found in the mcgraw hill civil engineering formulas textbook, section modulus = i / c = π (od^4 - id^4)/(32 * od) the results are totally different. has anybody done any bending moment checks on large pipes/cylinders? thanks. find a job or post a job opening mcgraw hill is correct. so i take it that m11 is wrong? for anyone who are interested, this is in the m11 pg 86. the first one is a close approximation for thin-walled pipes. for instance, if i use it to find the modulus of a 30" diameter, 0.05" w.t. pipe, i'd get: 15^2 * 0.05 = 11.25 in^3 using the mcgraw formula: (30^4 - 29.9^4)/(32 * 30) = 11.19 in^3 a change of less than 1/2 of a percent. it doesn't work so well when the wall gets thick compared to the diameter, though: 10" diameter, 1/2" w.t. pipe: 5^2 x .5 = 12.5 in^3 now if i use the mcgraw formula: (10^4 - 9^4)/(32 x 10) = 10.75 in^3 which comes in at 16% off... if you "heard" it on the internet, it's guilty until proven innocent. - dcs |
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