unit density of sawdust in a duc
 

unit density of sawdust in a duct?
hi,
i am designing some structural support for ductwork which may have an accumulation of sawdust inside of it. does anyone have a range of unit densities that i might use for calculating a load? i realize that it depends greatly on the moisture content of the sawdust, but i would like some numbers in order to get a feel for the design load.
any help would be appreciated.
thanks,
richard querin
i would start with the unit weight of wood (before cutting), which would be 35 pounds per cubic foot for douglas fir. hardwoods such as oak would be a bit heavier. in the sawdust form, i would estimate the density at about one-half to two-thirds, depending on how tightly packed it is.
from the aitc timber construction manual:
douglas fir 33.5 pcf @ 12% mc and 35.2 pcf @ 20% mc
hem-fir 26.6 pcf @ 12% mc and 27.7 pcf @ 20% mc
s. pine 36.3 pcf @ 12% mc and 37.4 pcf @ 20% mc
red oak 44.0 pcf @ 12% mc and 44.9 pcf @ 20% mc
mc = moisture content
i agree with kramer that somewhere between .5 and .75 of the above values would seem resonable. the other alternative is to weigh a 1 cf sample of the sawdust. also, some manufacturers of dust collection systems might have a number that they use.
just a thought! good luck.
thanks for the info.
the client has supplied a value of 15pcf and this seems reasonable compared to the values you've given above (the sawdust in question is in quite a dry state).