Value of composite metal beams?

[RLewis42]

It has been my understanding when working with natural wood beams/joists, that for example, two 2x12 members over a 12' span gain significant strength when they are fastened (nailed, glued or both) together rather than just lying side by side touching one another.

Is this phenomenon transferable to metal members or does it just work because of the random nature of wood fibers?

For example, if I have two 12' 1"x3" 1/8"wall rectangular tube 6063 aluminum joists suspended on each end, does the act of bolting them together with three 3/8" bolts at the 3' 6' and 9' locations add significant strength even though the 3/8" holes in the 3" vertical walls could conceivably weaken the joist somewhat? The two joist are already bolted together at both ends.

I am not looking to calculate the exact difference, just wanted to know if the concept transfers to metal.

thanks for your ideas,

 

[Dr. Courtney]

Metal gains a bit of strength in all directions with fastening, but not as much as wood.

 

[SteamKing]

It has been my understanding when working with natural wood beams/joists, that for example, two 2x12 members over a 12' span gain significant strength when they are fastened (nailed, glued or both) together rather than just lying side by side touching one another.

Is this phenomenon transferable to metal members or does it just work because of the random nature of wood fibers?

For example, if I have two 12' 1"x3" 1/8"wall rectangular tube 6063 aluminum joists suspended on each end, does the act of bolting them together with three 3/8" bolts at the 3' 6' and 9' locations add significant strength even though the 3/8" holes in the 3" vertical walls could conceivably weaken the joist somewhat? The two joist are already bolted together at both ends.

I am not looking to calculate the exact difference, just wanted to know if the concept transfers to metal.

thanks for your ideas,

You'd have to check the loads in the bolts and the holes in the walls of the tubes to figure out how much stronger two beams bolted together would be. Three bolts over a 12-foot length seems a tad light.

For full strength connections, welding would normally be recommended.