6"x6" post strength
6"x6" post strength
(OP)
Help my basement may not be structurally sound. Can anyone tell me how much load a 6"x 6" pressure treated post 8'in length is rated to hold? We have not been in the house long. The post is bowing slightly. The truss design estimates 30,000# on this post.






RE: 6"x6" post strength
Fc = 525 psi and E = 1.2. L/d ratio is 13
Allowing for buckling, allowable compressive stress is roughly 475 psi, Area is 30 sq in, so the allowable force in the post is 14,300 lb. However, if the post is a stronger grade, the strength goes up quite dramatically.
The first thing you should do is check the grade stamp.
The flexing could be due simply to drying, because it is unlikely that the house is loaded to anywhere near design load.
RE: 6"x6" post strength
RE: 6"x6" post strength
Timber Construction manual specifies Euler's formula with a safety factor of 2.727, that is;
Sigma(allowable)=0.3*E/(L/d)**2
0.3*E/(L/d)**2=P/A
=P/d**2
solve for d, d=5.26" ok use d=5.5 nominal dim
checking normal stress;
Sigma=P/A
=30,000/(5.5)**2
=991 psi
requires Compression Parallel to Grain "Fc" > 991
the only grade that meets this is Dense Select Structural
see http://www.southernpine.com/designvalues2.htm
I have never seen this grade used in residential application, so one can suspect the post is undersized.
RE: 6"x6" post strength
RE: 6"x6" post strength
As for your bow, I think that is due to shrinkage.
RE: 6"x6" post strength
RE: 6"x6" post strength
I would consider just adding an additional 6x6 next to the existing post bolt the two together.
RE: 6"x6" post strength
http://www.wwpa.org/pdf/TN9.pdf
RE: 6"x6" post strength