Multiply Wood Beams Cut Between Continuous Supports

[ANE91]

I’ve got 4 supports equally spaced roughly 7 feet apart. This is near the max length a contractor can readily source, so I often end up with random cuts, cantilevers, and discontinuities. Even when I’m lucky and the contractor has somewhat nailed and clinched the plies together, the “splices” are incorrect.

Are there best practices for specifying these beams and explaining the important bits to the contractor (e.g., staggering the joints, using straps instead of nails, etc.)? Think basement ceiling (residential).

 

[XR250]

I only call out continuous if I actually need it. Usually on short spans strength controls so continuity does not help that much. I call out all splices to occur over supports. The AHJ usually calls them on it if they don't. Then I have to look at the splices and cantilevers. You could also just call out 3 members when you need 2 to give you some headroom in these situations.

 

[Ron247]

I assume you are talking about a multi-layered dimensional lumber beam. When I use continuous values, I also require 1 additional layer. If it calcs to 3 layers, I use 4 etc. I also tend to require adjacent layer splices to be staggered 3 to 4 beam depths. I also tend to specify a preference for splices be at the 1/3 or 1/4 points. The type of loading affects the use of that rule.

 

[ANE91]

Adding another ply would save me a lot of headache. It’s not even over-engineered — it’s engineered specifically for a particular type of contractor. Thanks all.

 

[Ron247]

Yeah, I have always viewed it as designing to the reality of what is reasonably available. If I don't work with 16' lengths or less, it sounds like I think you can buy a 32' 2x12 without special ordering it. As for as I recall, 20' is the max I have ever seen special ordered.

 

[jerseyshore]

We too call out for splices to occur over supports. And for 99% of basement girders I'm not designing continuous members. With similar spans I've never seen an issue. Only time I'll check both continuous beams and spliced beams are for multiple span members that have unequal spans. I make sure those work both ways. Some guys like to work with 24 footers and others prefer 8 ft sections. I can't be bothered to worry about it so if I think a problem can occur one way or the other I check both.