This study investigates the performance of 38 by 89 mm (1.5 by 3.5 in.
) parallel-strand lumber columns. Currently, the 1991 national design
specification of the American Forest and Paper Association far columns
includes a c factor that describes the interaction of columns between
the pure crushing and stability failure modes. For wood material, c i
s a combination of member straightness, material inhomogeneity, and st
ress-strain plasticity. The objective of our study is to determine an
appropriate c value for parallel-strand lumber. Columns of several len
gths are axially loaded to failure. Based on the nonlinear least-squar
es fit of column results, adjusted to a common moisture content, the m
ost probable value of c for parallel-strand lumber is 0.86. This incre
ased c value is attributed to the greater homogeneity and straightness
of the manufactured columns.