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Double ceiling beam

Double ceiling beam

Double ceiling beam

(OP)
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.



RE: Double ceiling beam

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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