Our company regularly performs structural repairs on 19th- and early 20th-century residential brick buildings in the Chicago area. This one was a three-story, 60-unit apartment building with wood-framed partition walls and floors and a nearly flat and severely underframed roof. The 2x10 joists, running front to back, didn’t need to sag much before they were bearing on 2x4 ceiling joists. The partition walls beneath this ceiling were only meant to hold up plaster and lath but had become bearing walls supporting roof loads. The added live and dead loads transferred all the way to the first-floor joists, which had zero support under them and, over the years, had been cut up by previous contractors. You can see the extent of the damage this caused in the photos at the top of the facing page. Most of the joists directly below a full-height partition wall at midspan had failed, with many joists splitting along the centerline. The failure was especially noticeable at knots and other defects, which create a weak link in the lumber.
The magnitude of these failures prompted our first step: erecting emergency shoring. The occupants in the three apartments above were moved out and all the plumbing and electrical lines running through the floor were removed.
Working to engineered specs, we began our repair work by digging and pouring footings for steel posts to support an I-beam that would provide the necessary support for the wall above. Before installing this beam, we secured an LVL ledger to the basement walls to provide extra bearing at the joist ends and sistered 1 3/4-inch-thick LVLs to the joists. These LVLs ran slightly past the midspan where the beam would go, and on each side of the beam, we staggered the LVLs on different faces of the failing joists to increase the bearing. With the LVL sisters in place and raised in line with the bottom of the floor joists, we could install the beam and post down to our footings. The photos and captions on the following pages describe the sequence of steps needed accomplish the critical steps in this repair.Read More