Comparing 2X12 and steel I beam

[jallcorn]

Recently bought an old building that was constructed with masonry load bearing exterior walls, wood trusses and wood 2X12's nailed together (either 3 or 4 or 5, depending upon which beam). Support posts are about 18 feet apart (the building is 60x100), 2 outer beams, 2 inner beams.

My intention is to ADD steel I beams with steel supports adjacent to the existing supporting wood beams. I will lift 1 corner of the building (truss ends) about 1.5 inches where a top plate has deteriorated. All other locations will be basically the same elevation or just minimally lifted to take out sag, etc.

Now the question: Assuming vertical supports every 15 to 18 feet apart, what size and weight steel I beam would be needed to approximate the support provided by 3 2x12's nailed together as a beam, and 5 2x12's nailed together?

[Rich]

That's probably going to take an engineer. I can give rough load capacities of a single 2x12 that you can multiply times the number of plies you have. I don't have any span tables for steel though.
I'll look around though and see what I can come up with.

[jallcorn]

The load cap. of a 2x12 would be nice. :D I would appreciate that figure. My steel supplier says the I beams can span 30', but that obviously depends upon the load. I have no intention of that long of a span. If I err, I want it to be on the strong side, but reasonable if possible.

The longest 2x12 I have found without special order is 16 feet. My current post spacing is longer than that by 2 to 4 feet. The builder is unknown plus age of building is unknown, but I do know it was constructed after 1916, they laminated it when it was constructed.

Roof is not flat, has some pitch, a crown (gable) plus 2 hips facing the opposing way to run water toward the corners. Roof is within parapret wall. Asphalt roof currently, wood deck, some plywood, some ship-lap or may be just 1x8 material.

JA

[Rich]

You can check this calculator out - just change the member type to Headers. http://www.cwc.ca/design/tools/calcs/SpanCalc_2002/
For 4-2x12's you're looking at a span of 12'10"
2-2x12's is 8'11"

There are recommended splicing patterns for extending headers longer. I'll see if I can find something.