6"x6" post strength 3

[kdisme]

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.

 

[Trussdoc]

Most P/T wood is Southern Pine. Assuming #2 grade, the
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.

 

[lsmfse]

What species of wood? Is the post framed into a wall? Is the 30 kip load Dead and Live load? Is any of this a roof load? Snow load? What frames on top of the post? In any case, 30 kips is a substantial load to be supported by a 6x6 wood post.

 

[boo1]

Is the construction new? How have you determined the 30,000 lb load? Is the end attached to the floor? Is the load centric?

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.

 

[boo1]

AITC Column Tables provide a calculated load that can be supported based on column size, length, and material properties see

https://www.aitc-glulam.org/TechnicalInfo/tables.asp?type=Column

 

[LPPE]

A 6x6 8' in height with no load duration factor and of Doug Fir #1 or better is good for about 28 kips. But usually bearing stresses of the beam on the post or the post on support will control.
As for your bow, I think that is due to shrinkage.

 

[trainguy]

Whatever has produced your bow, you should include a bending component in your calculation, which will reduce your allowable stress! Don't screw around on the internet, get a contractor in right away, and maybe even a structural engineer. You're talking about a huge loss of this thing buckles.

 

[boo1]

In America, typical 6x6 pressure treated (PT) are southern yellow pine (SYP). I agree with "Trussdoc", bow is drying and actual loading is much less that design. (Straight 6x6's are difficult to find)

I would consider just adding an additional 6x6 next to the existing post bolt the two together.

 

[boo1]

I found this link,

http://www.wwpa.org/pdf/TN9.pdf

 

[kdisme]

We have reinforced the post. Thanks for your help. Boo1 those charts were exactly what I was serching for. They correlated right on with trussdoc's calculations. Thanks