Seismic main beam connection
In a suspended ceiling for earthquake prone locations, a line of seismic main beam connections of the invention between main beams separates the ceiling into segments that move independently of each other during a quake, to limit a build-up in ceiling momentum. A slotted fishplate in the connection is set to keep the beam ends stable about a gap before a quake, and slidably connected about the gap during a quake.
1. 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.
2. The seismic main beam connection of claim 1 , wherein the necessary force to unseat the rim from the hole is set by the tightness of the screws extending through the slot and screwed into the other of the pair of main beams.
3. The seismic main beam connection of claim 1 wherein a cover plate is slidably secured over the bottom of the flanges of the ends of the pair of main beams in the connection.
4. The method of installing the seismic main beam connection of claim 1 in a suspended ceiling having a group of longitudinally connected main beams extending parallel to one another; comprising
a) first constructing a suspended ceiling with a fixed connection longitudinally connecting main beams; and
b) then cutting out a section of a fixed main beam connection; and then
c) inserting the seismic main beam connection defined as the improvement in claim 1 , in the cut-out section of the main beam connection.