wood laminated posts - does this work

huangyhg

wood laminated posts - does this work?
there is a laminated post company which is manufacturing laminated 2x wood posts for pole barn type structures. we are in a 90 mph wind zone.
they seem to show that they can use a (4)ply 2x6 post for wall heights to 24' with posts at 8' oc. (#1syp material)
30 psf ll, 7 psf dl, 90 mph, negligable earthquake
they specified a maximum building size of 32' width.
i see the design wind load for the "non-corner" part of the building as being 13.6 psf suction (per ibc table 1609.6.2.1(2)), which gives approx 110 plf.
if the post is properly embedded in designed footing, then i would use a fixed base and pinned top support.
max moment = wl^2/8 where l = the sidewall ht=24'
m=7850 ftlbs applied due to wind
according to my nds 2005, i see #1syp 2x6's as fb=1650, e=1700, fc=1750
s=33in^3 if the post is turned the strong direction to resist wind.
(assuming the post is laterally braced (weak axis) 2' on center by girts, but only braced at the floor and ceiling level (24') in the strong axis.
i see the moment capacity =4540 ftlbs at 100% or 6040 ftlbs at 133% wind stress.
so the wind stress in bending is 173%
so i think the post fails without even adding the gravity loads.
i have that the post has a design axial load of 11.4k.
if the building is framed with trusses (and posts only on the perimeter) in the 32' direction, with 30 psf ll, 7 psf dl, and 90 mph winds, the applied axial load under combined wind + dead + live is approx 5.3k.
so the axial load is using 47% of the design stress.
(i use column ke=0.8 for fixed base posts-pinned at the top)
i missing something? do you see any way that they can make this engineering work?
i don't see how they can have engineering to make this work.
a couple suggestions--
the load combinations should be:
* d + l
* d + w
* d + 0.75l + 0.75 w
the load duration factor for load combinations involving wind is 1.6, not 1.33.
dave-
thanks-
it looks to me like the repetitive member factor applies only for   
just look at the nds.  the load duration factor for wind is 1.6 (this is the cd factor)
i agree that it doesn't work. i just ran your column in woodworks sizer, assuming a 6x6 post (close to what you've got), #1 syp, fixed bottom & pinned top, continuously braced in it's width direction, unbraced in it's depth direction, with the wind and axial load you describe. i input the axial as all live load to get the higher load duration factor. axial load eccentricity = 0. my sizer version uses nds 2001. it is giving me a combined stress ratio of 2.85 using ibc load combinations.
also, why are you assuming pinned at the top? is the building braced?
ok i see the 1.6 wind factor now-
sorry- i had a brain fart the 1.33 was a carry over from the old codes.
table 4b cf notes mentions that size factors have already been included in the table values, but mentions that if we got to be more than 8" wide (which we are not) that additional factors may apply.
careful... don't confuse the "load duration factor, cd(nsd 2.3.2) used with asd and the "time effect factor", lamda (nsd 2.3.7) used with lrfd.
spats- thanks for the info.
i am assuming that the building shell and roof acts as a diaphragm
allisch,
if this is a pole building and the posts are cantilevered out of the ground then the bending moment is wl squared over 2, not over 8.
also, when calculating the column stability factor,cp re  
old paper maker-
wl^2/2 would mean that they have no lateral support at the top.
i am giving them the benefit of the doubt that they can get the diaphragm strength from the sidewalls and roof to have the top as a pinned connection.
old paper maker-
but you do bring up a good point-
they also may have problems getting the roof to take the diaphragm loads to the sidewalls.
but that is a whole different can of worms.