Originally Posted by swindmill
How do I measure the deflection?
From the floor underneath.
With the load in place measure the exact ceiling height. Then remove the load and look for an additional fraction of an inch in height.
I usually clamp two scrap sticks together and set this composite pole to the exact ceiling height when loaded, and then eyeball the gap that results when the load is removed.
For L/Δ = 360, for a span L of 15' [180"], Δ = L/360 = 180/360 = 1/2" when under the design live + dead load, but this is for a distributed load. A concentrated load gives you different results but I think it can be still be used to figure the equivalent dist. load.