Do you spec glu-lam beams in your drawings to resist uplift? 1

[reverbz]

Hey guys,

Not sure if this is necessary or not but an older engineer in my office insist that if a glb is resisting uplift it needs to be called out or specced out on the drawings as GLB's top plies aren't designed for that. Is this true? Do you guys do this on your drawings?

Thank you!

 

[ANE91]

The layup determines the GLB performance. Continuous GLBs have balanced layups. It makes sense; you want higher-grade wood on the top and bottom. Speccing it out is the way to go.

 

[SE2607]

It depends on the actual stresses. For example, if a GLB is graded as 24F-V4. The allowable tension stress on the bottom face is 2,400 psi and the allowable tension stress on the top face is 1,850 psi. So, if the net tension stress in an uplift condition does not exceed 1,850 psi (plus adjustment factors), then the 24F-V4 would be ok. Personally, I consider this when designing GLBs with short cantilevers. For reference, see NDS Table 5A.