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Repairing Over-Notched Floor Joists.

Some time in the 1990s, this Charleston, South Carolina home was expanded with an addition at the rear of the residence. The expansion was constructed to mimic the original construction. Unfortunately, the foundation wall was constructed to support 2x6 floor joists, not the 2x10 floor joists required for the floor span. The contractor at the time appeared to have decided that the easy answer to this problem was to simply notch the 2x10 floor joists down to 2x6s at the CMU foundation wall. As could be expected, the notched 2x10s eventually cracked as a result of shear stress at the support point.

Typical shear crack in the 2x10 floor joist

The cracks were relatively uniform across the floor system and extended 12 to 24 inches into the floor joists. Rogers Engineering was retained to prepare a repair plan for the damaged floor joists. In other areas of the residence the repair contractor repaired the damaged, rotten, or under-sized floor joists by "sistering" properly sized joists adjacent to the damaged joists. "Sistering" would not work in this case because the new joist would also have to be over-notched. Further complicating the repair, the various plumbing and electrical components made installing full-length floor joists virtually impossible without re-plumbing and re-wiring the residence.

Since the joist cracking was limited to the high-shear portions of the joists, the joists were an excellent candidate for a partial repair. In this case, it was determined that L5x5x3/8 angle bolted to the original 2x10 joists provided sufficient shear capacity to restore the structural stability of the floor system. The angle was through-bolted to the existing 2x10 floor joists with a staggered pattern, and the length of the angles were sufficient to distribute these loads back into the 2x10 joists. The repair contractor had a local steel supplier pre-drill the angle to speed installation. Each angle had top and bottom holes drilled so the angles could be interchanged with the front and rear walls.

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