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StructuralEng, Consultant
Category: Structural Engineering
Satisfied Customers: 6809
Experience:  Structural Engineer
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Live and Dead Bearing foot span of triple 2x12 PT lumber Building

Customer Question

Live and Dead Bearing for 24 foot span of triple 2x12 PT lumber
Building foot bridge to span 24 feet and using 3 sets of these triple 2x12 beams to form a four foot wide base of the bridge.
Submitted: 9 months ago.
Category: Structural Engineering
Expert:  StructuralEng replied 9 months ago.
Hello. How are you doing? I'll be happy to assist you.
Expert:  StructuralEng replied 9 months ago.
You need to know the live load capacity of the bridge?
Customer: replied 9 months ago.
Yes, we want to be sure these 3 sets of tripled up 2x12s will support the 2x6 top decking materials and then what live load it will support.
Expert:  StructuralEng replied 9 months ago.
Will all plies of 2x12 be the full 24' length?
Customer: replied 9 months ago.
No, we plan to use 2 x 12 x 12foot pices interwoven together and then glued and bolted to make triple wide beam. so 2 2x12x12 end to end with one 2 x 12 x 12 in center and 2 x12 x 6 foot on each end, then third layer is 2 more 2 x 12 x 12 foot end to end. all this bolted together and glued.
Expert:  StructuralEng replied 9 months ago.
What I can do is this. I can give you the capacity assuming three double 2x12. Interweaving them the way you describe is common, but is a very different behavior and is heavily reliant upon connections to transfer forces across the butted ends. At best, ***** ***** two 2x12 working for you where two are butted together, and you'll need to be sure the connections are designed in a way to make it true that you have two and not less.Is that reasonable?
Customer: replied 9 months ago.
Yes, should reasonable.
Expert:  StructuralEng replied 9 months ago.
Assuming a dead load of 15 psf, that would give you a live load capacity of 30 psf, assuming doug-fir no. 2 pressure treated