12" steel i-beams---40 ft long---1/4" web?
Question:will these beams hold more load capacity if placed side by side or placed on top of each other?
Answers:
side by side is the only way to fly. As the load is applied the beams will deflect a bit and twist a bit.
If you stack the beams, this twisting may cause the top beam to squirm around and slide off, or make the load on the lower one uneven.
Are you thinking of a 40 foot span, unsupported in the middle?
Why not go wood? An engineered wood beam is stiffer (less sag, much less vibration) than steel, and is ideal for long span domestic building.
One trade name is Silent Floor.
Mark is right about the side by side thing. However, eventhough I sell engineered lumber for a living, I wouldn't recommend a wood beam that's 40' long. It would be massive! And, by the way, you should consult a professional before deciding on the size of beam you need for a project. From the sound of things, you should contact an engineer.
you need to determine the loading for the beams before you ask the question. if you want to support an engine hoist stacked and bolted together through the flanges would be best. if you want to create a bridge to drive across, side by side. bridge is bad example. lets say you want to make a deck. 2X12 @ 24" oc. span 12' using the steel girder to clear span 40' at bearing. the tributary load is 6' x 40' x dead load of deck + live load of 60 PSF. the reaction of any given girder is the answer / 2. now get the load into the ground (foundation) is dependant upon the allowable soil pressure of your ground, code minimum is usually 1000 PSF. bridge is a bad idea unless your talking pedestrian access (5' wide max.) as bridges need to be designed to highway loadings for emergency vehicles. check w/ your local building department.
40 ft beams with no support and a heavy load are going to give a bit. guy above is correct in suggesting engineered beams.
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