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Re: Light Fixtures -- Seismic

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Almost all tenant improvements for offices involve suspended ceilings with
light fixtures. During a strong earthquake, if we don't provide seismic
bracing for this system, it is possible that it will be in a condition that
will be unsafe for the tenants to occupy. There may or may not be extensive
structural damage but it may appear unsafe. I would require seismic bracing
for suspended ceilings with or without light fixtures.

For light fixtures only, I would use engineering judgement. Ask yourself if
there will be damage or even the appearance of damage or an unsafe condition
after an earthquake. If the fixtures are far apart, away from the walls, and
with strong enough vertical support that they will just sway independently
during an earthquake, I won't require seismic bracing. If they are close
together or near a wall or anything they may hit, I'll require seismic
bracing. Remember to consider that seismic forces may be an up-down motion so
design your vertical supports for such forces.

If the contractor questions your decision or judgement, tell him that you go
by your minimum standard as engineer of record and not by the UBC minimum. If
he insists on doing it his way, tell him it is his responsibility and you are
not approving anything  other than what you feel is structurally adequate.

Ernie Natividad