Patent ID: 7788872

Claim:
In a seismic main beam connection between a pair of aligned main beams in a ceiling grid for a suspended ceiling, a main beam having in cross section a) a bulb, b) a web depending downward from the bulb, and c) a pair of flanges extending in opposite directions from the bottom of the web; the improvement comprising a gap between the ends of the pair of aligned main beams; and a fishplate extending across the gap a) fixed to the end of one of the pair of main beams, b) having a slot extending longitudinally of the main beams, with c) screws extending through the slot and secured in the other of the pair of main beams; and d) a raised circular rim in the fishplate that seats in a hole in the other of the pair of main beams; wherein in the seismic main beam connection as constructed, the pair of main beams are stable about the gap, with the rim on the fishplate seated in the hole in the other of the pair of beams; and in an earthquake, the pair of main beams are free to oscillate longitudinally toward and away from each other about the gap when the force of the earthquake unseats the rim in the fishplate from the hole in the other of the pair of main beams.