huangyhg

beam formulas.
i have not calculated a beam in 20 years and all of my books are out of reach. i am looking for the formulas to calculate bending moment on a simple beam supported at both ends with a uniform load combined with a point load in the center. this is to get preliminary sizing for a glulam beam spanning 25 feet, supporting the uniform load of the floor above and a point load from a column placed in the center of the span, which supports the ridge beam of the roof above that floor. my memeory says pl/4 & wl(squared)/8
also what is a source for moment of inertia tables for glulam beams? many tables size the beams by spacing, combined with span, for various floor loads/sq.ft., which is no help when there is a point load to be considered also.
thanks
check out our whitepaper library.
your memory serves you well for the bending moment formulae -- it is indeed p*l/4 for a point load at midspan and w*l2/8 for a uniformly distributed load on a single-span simply supported beam.
i don't work with timber though so can't help you with the beam properties.
go to wwpa.org, and download their free excell-based beam and post design suite.
or go to:
oops-
nothing for glulams at wwpa.org
sorry.
you don't need to memorize a formula for those two loading conditions- just take half the beam as the freebody, and sum moments about the center point.
moment of inertia of a glued lam beam is no different from a moment of inertia of any rectangular element.
i = bd^3/12
section modulus, likewise.
s = bd^2/6
g'day
not knowing much about the structural strength of wood products, what would abelgus use as his allowable ? ... it doesn't sound like it's at wwpa.org ?
allowable stresses depend on the combinations of laminations and species of wood. using 24f-v8 combination using douglas fir, allowable bending stress (both tension size and compression side) is 2400 psi and allowable shear stress is 190 psi.
24f-v4 compression side allowable bending stress is 1200 psi.
i am referencing from 1997 nds. the latest edition should have the same values (i think).

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