Suitability of Tulip Poplar for Timbers
Can a large Tulip Poplar tree yield large members suitable for structural use in a timber frame? March 28, 2010
Question
A client has a standing poplar (tulip) 100' tall and about 4' diameter. It will be taken down. Can it be sawed into reliably straight 6 x 12 timbers at 18 to 20 foot lengths? How many units can we get out of the tree? Do you know the working allowable stresses for this wood?
Forum Responses
(Sawing and Drying Forum)
From contributor M:
It's not usually used for beams as it is very weak. It would make better siding.
From Gene Wengert, forum technical advisor:
Yellow-poplar is used and is approved for structural usage. Strength values are published along with many softwood species in many texts and architectural references. The clear wood values for oak (one of the strongest species in North America) are MOR (ultimate bending strength) = 14,300 psi and the MOE (stiffness) is 1.82 million psi. Yellow-poplar is 10,200 and 1.58, which is not too bad at all. Eastern white pine is 8600 and 1.24. So, basically, it is a good choice from a strength point of view.
Will it stay straight? Many pieces will not, as the tree has quite a bit of stress in it. How many pieces? A sawmiller will be able to estimate that for you after he/she looks at the log. Keep in mind that knots reduce the strength, but a 24" diameter tree will likely have a lot of clear wood, making strong wood.
From the original questioner:
Again thanks. This 48" diameter tree is not a forest tree. It has been growing in a relatively open suburban area. Does that affect the kind and amount of stress in the tree? Do yellow poplars have greater internal stresses than other trees in its strength range?
From Gene Wengert, forum technical advisor:
Yes.
