huangyhg

double ceiling beam
can anyone give me a reference for lateral stability of unbraced ceiling beams? i have two horizontal beams with king posts @ the one third points. i plan on spacing the beams 3 1/2" apart and providing a spacer block sandwiched between the clg beams below the king posts. spacer block will be bolted thru the clg beams with an all-thread.
beam stability, cl is controled by lateral support, not bearing. without lateral support or proper design considerations, the compression side of a beam may buckle prematurely at a load much smaller than what was intended in a normal bending mode. but, the height to thickness ratio of typical wood headers (2-2"x12" or 2"x10"), 3:1 or 4:1 ratios requires ends of members by blocking, bridging, hangers to have cl=1.0. typically the number of trimmer and cripple studs are selected by the span and provide this support. additionally the interior and exterior sheathing provides additional support.
for height:thickness to assume cl=1.0
2:1 and less case, no supports are required
3:1 or 4:1 case, at ends of members by blocking, bridging, hangers.
5:1 case, then the lateral stability requirements are:
a. the compression edge is held in-line the entire beam length
b. the member ends are held in position with full depth blocking, hangers, or bridging.

beam stability factor equation:
cl=((1+q/1.9)-((1+q/1.9)**2-q/0.95)**1/2)</= 1.0
g=fbe/fb*
fbe=(kbe/ey'/rb)**2 kbe= 0.438 lumber, graded
0.610 glulamms
ey'=ey(cm)cl

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