Although steel I-beams are common in commercial construction, they're not often seen in homes. Perhaps that is because wood is strong enough to fulfil most home construction needs. Although I-beams hold up a lot of weight over a long span, steel has that industrial look. Fortunately, there is an industry of faux wood beam products so realistic that no one will ever know those are not hand-hewn or rough-cut structural timbers overhead. The kind we cover is three-sided polyurethane and comes in many styles and wood colours, oak to walnut.
Measure the length, height and width of the I-beam. Add 2 inches of width to your measurement. The inside width of the faux beam you buy will match your last measurement. The inside depth of the faux beam must meet or exceed the height of the I-beam's cross section. Buy a faux beam long enough to cover the entire I-beam, or two lengths that will cover the I-beam with a single seam.
Fasten wooden cleats to the surface along the entire length of, and against both sides of, the I-beam. If you are going through ceiling drywall with no wood backing, use toggle bolts. Drill holes in the drywall large enough for the toggles, and matching holes in the cleats just large enough for the bolts. Push all the bolts through the cleats and thread the toggles onto the bolts. Have a helper hold one end of the cleat up to the ceiling while you push all the toggles through the ceiling holes. Fasten the bolts.
Keep enough drywall screws handy to space them 1 foot apart down the length of the beam, on both sides. The screws should be just long enough to go through the faux beam sidewall and 3/4 inch into the wood cleats. Push the faux beam over the I-beam on one end and have your helper do the same on the other end. Use the Phillips bit in the drill to drive one screw through the edge of the faux beam about 1/2 inch from the drywall surface. Do the same on the other side. Repeat at the beam's middle and other end. Now drive screws every 1 foot.
Snap faux iron straps over any seams.
Hand-hewn may be called adzed or heavily distressed depending on who makes them. Faux timbers come up to 20 feet long. If you have a longer span, fake antique black iron straps are available to cover the seams. Half-round timbers are available as well. Faux beams cut easily with a hand saw.