Interesting mass timber problem

I have an interesting problem that tilts a little toward the mass timber world. My residential client has a lot of resources related to sawmills, which can provide an endless supply of White Oak and Shortleaf Pine lumber. His idea, which sounds kind of fun, is to build up a 3" thick plate out of 1-1/2" X 3" lumber, alternating oak and pine, and use this as a combination floor (above) and ceiling (below) on top of beams. I’ve seen this done with 1-1/2" lumber on 48" center joists and it looks nice. Each section would be 1-1/2" wide, 3" deep, and nail laminated into planks maybe 12" wide and 16’ long. These would be installed over beams instead of floor joists, with the top planed and sanded to make the finish second floor, the bottom side exposed to the room below. The alternating wood colors will make a really distinctive look.

Just some preliminary modeling (pretending it’s all Southern Pine), and it might be able to span maybe 8 feet. But I’m stumped as to how to model this rigorously in Clearcalcs. I can see how one might model one type of wood in “Generic Wood Beam”, and check “number of plies” to make a 12" wide “beam”. How would one handle the alternating wood species? Maybe do a separate spreadsheet calculation to average out the different strengths of material into one number?

Hi @Lawrence, I’m sorry we didn’t get back to you earlier on this!

What a cool project indeed, those floors are gonna look incredible and certainly unique. Hope you can send some pictures once done.

Now for the fun part of modeling in ClearCalcs. This is definitely a bit outside the “standard” stuff we’ve made the calculators for - I think your idea of averaging out capacities might be a good one, though I’m also wondering if entirely adequate given brittle failure mode for wood. Conservative assumption would definitely be to treat the entire plank as pine, as you mentioned you did already. Beyond this - I think it’s a fair question of engineering judgement and comfort