Complex sentence: His open-web steel joist, patented between 1924 and 1926 and known as the Massillon Steel Joist, was a revolutionary assembly of steel joists and top slab for support of floors, ceilings and roofs.
Split into simpler sentences: His open-web steel joist, patented in 1924, was known as the Massillon Steel Joist. Macomber's invention was a revolutionary assembly of steel joists with a top slab used to support of floors, ceilings and roofs.