Round Wood Columns 2

[DaveVikingPE]

Round wood columns, that is load-bearing hollow round timber columns, as sold by for example, Cox Lumber or other architectural detail vendors:

are they spaced columns?

or

are they built-up columns?

is there design guidance for these? The manufacturers give load ratings for their columns, how are they determined?

 

[RG88]

The ones that I have seen at the local lumber yards are built up, in a sense. They are typically constructed by the old coopers technique, i.e., construct a multisided polygon and round the vertices down until you obtain a round shape. As far as load ratings go, well this is definitely something that I would press the mnfr or distributor for. Given that you are (will be) purchasing one of their products, you should be able to get a detail sheet with proper framing details to obtain the load rating provided. The building official will probably require this data.

All to often, I have seen the mnfr provide ultimate loads for wood and FRP columns, only to find out that there are substantial and uncorrelated reduction factors for eccentricty, end connections, and loading configuration. All of which, cannot be calculated by standard means, as the mnfr obtained the results experimentally.

If all else fails, you can place a steel pipe column inside to carry the load. For most residential applications in the foyer or the front porch, the columns will not be loaded to the mnfr maximums. I would exercise caution using the columns at any loading near the mnfr provided ultimate.

 

[DaveVikingPE]

Thanks, RG88!

The info I have/am using showed a "maximum allowable load" of X kips based on a particular column diameter. I noted that this load was the same regardless of column length; columns could be purchased @ 6', 8', 10', 12', 14', 16' and 18' lengths. Hmmm... So I applied the maximum loading to the maximum length and assumed the column was "built-up;" I assumed no eccentricity, assumed 10-year load, assumed wet conditions, etc., and considered the loading on one of the column pieces.

The Fc I came up with matched the manufacturer's, kind of blowing me away.

That was for my own satisfaction, but I'm contacting the manufacturer nevertheless. I sure wish the column companies would supply some good design info with their sales brochures.

 

[oijammu]

You want the wooden external surface for aesthetic purposes only! Why dont you infill it with reinforced concrete.

 

[DaveVikingPE]

Good point on the lack of connection details. Seems they count on the designer to specify using their cast iron or steel bases and tops. As far as UV and moisture penetration are concerned; these are wood, not the FRP columns, and the effects of such are well known.

Filling the column with concrete probably isn't a good idea since they lack reinforcing hoops or similar "form" appertanances.

The vendors do, however, state in their literature that the columns are "load-bearing" and, as I mentioned, show allowable loads and the columns are warranteed. If this means the vendor must certify the installation of the columns then fine; they're putting their stamp on the product. Does this mean I'm satisfied? No. I want to discuss this to my satisfaction with the manufacturer's engineer. In the case of the building I'm designing, at present hollow round wood columns have supported an active second storey for 100 years.