The final physical characteristic of wood affecting its design strength is slope of grain. This is particularly important in Southern Yellow Pine where grain direction can vary greatly. Slope of grain is a measure of how aligned the long axis of wood fibers are to the long axis of the cut piece of lumber. Greater alignment means greater longitudinal strength.
Slope of grain is determined as a general slope over the length of the board, and local deviations (around knots for example) can be ignored.Slopes are reported as a ratio - 1:8 is not very straight, deviating up to an inch over just 8 inches of length. 1:16 would be very straight by comparison.
*Wednesday's Word Of The Week is a feature on Unalam's Wood Times Blog. Each Wednesday our structural engineer, Rik Vandermeulen, will discuss a new term associated with glulam manufacturing. He will do this until we run out of words. If there is a timber or glulam term that you have heard of and want to know more about, let us know in the comments.