bigmakattak
Civil/Environmental
- Mar 28, 2010
- 4
I m retired civil and trying to help my son with an engineering study for 7'6" high fence with 4 x 6 Doug Fir posts at 8' o.c. already built in Oakland, Ca area.
Will probably need a California P.E ( I am not) for this, but I have done some hand calculations.
Basics:
Used California Building Code and ASCE 7-95 to best of my abilities. 92 mph wind from CBC chart and reduced it to 71.3 mph per allowed ? ( q times square root 0.6) working stress method. Then used ASCE methods for wind loadings Using the Kz of .67 and Iw of 0.87 and wind formula I end up with 7.6 psf across the 60 Sf contributing area to each post. Treating post as cantilever beam I end up with 61 plf distributed as uniform load on the post resulting in 20 inch - kip of bending moment and 1800 psi bending stress on the Doug Fir post. The 4 x 6 is weak axis bending for the primary wind direction. This doug -fir is probably No. 1 at best with a capacity of 1500 base value, but able to factor up by 1.25 or 1.6 possibly for duration of load?
Also, concrete post bases are 28 inch deep but only 16 inch diameter. So doing some quick gorilla math using a simplified triangular soil resistance pattern I end up with 350 psf lateral pressure applied and with an assumed allowable 200 d allowable (466 psf). Looks like it works. Sound reasonable?
So I post this in hope of getting some opinion as to whether I am at least in the ball park on this whole thing regarding wind base pressure and appropriate reduction factors , wood allowable stresses and factors and so on as I have not sharpened the pencil or greased slide rule in a long time.
Thanks.
Will probably need a California P.E ( I am not) for this, but I have done some hand calculations.
Basics:
Used California Building Code and ASCE 7-95 to best of my abilities. 92 mph wind from CBC chart and reduced it to 71.3 mph per allowed ? ( q times square root 0.6) working stress method. Then used ASCE methods for wind loadings Using the Kz of .67 and Iw of 0.87 and wind formula I end up with 7.6 psf across the 60 Sf contributing area to each post. Treating post as cantilever beam I end up with 61 plf distributed as uniform load on the post resulting in 20 inch - kip of bending moment and 1800 psi bending stress on the Doug Fir post. The 4 x 6 is weak axis bending for the primary wind direction. This doug -fir is probably No. 1 at best with a capacity of 1500 base value, but able to factor up by 1.25 or 1.6 possibly for duration of load?
Also, concrete post bases are 28 inch deep but only 16 inch diameter. So doing some quick gorilla math using a simplified triangular soil resistance pattern I end up with 350 psf lateral pressure applied and with an assumed allowable 200 d allowable (466 psf). Looks like it works. Sound reasonable?
So I post this in hope of getting some opinion as to whether I am at least in the ball park on this whole thing regarding wind base pressure and appropriate reduction factors , wood allowable stresses and factors and so on as I have not sharpened the pencil or greased slide rule in a long time.
Thanks.