The term,” yellow pine”, can refer to several pine species or groups of species which tend to grow in similar forest types and yield similar strong wood. In the Western US, yellow pine refers to Jeffrey pine or Ponderosa pine. In the United Kingdom, yellow pine refers to Eastern white pine or Scots pine. In the Southern US, yellow pine refers to a special group of trees known as the Southern Yellow Pines, these are mostly longleaf pine, shortleaf pine, slash pine, and loblolly pine. This group of pine species has a special character and history of its own. Continue reading “All Pine Trees Aren’t the Same: It May be One of Several Species”
How was SPIB formed?
The Southern Pine Association was formed in 1915 to provide a common set of grading standards for the industry. Prior to the formation of the SPA, each regional pine association published their own grading rules using different grades and sizes. With the advent of World War I, the Department of Commerce required standardization of lumber sizes and moisture specification, and the SPA was instrumental in leading this industry transition. In 1941, as courts sought to separate inspection and grading services from trade associations, the Southern Pine Inspection Bureau was created as a non-profit organization with an elected Board of Governors. SPIB incorporated in Louisiana in 1969 and since 1993 has been incorporated under Florida law. All grading rules for Southern Pine are maintained by SPIB and are the standards for the entire Southern Pine industry.
Continue reading “Your Rules Writing Agency for Southern Pine”
What is density of lumber?
In a general sense, density is defined as mass per unit of volume. For lumber, that could be given in units of pounds per cubic foot, or expressed as specific gravity (or relative density) where the density of the lumber is divided by the density of water (also in pounds per cubic foot) and expressed as a percentage: i.e. 0.55 for Southern Pine.
Continue reading “Density of Wood”
What is moisture content of lumber?
The amount of moisture in wood is often expressed as a percentage of the weight of the wood when the oven-drying method is used. When a tree is still growing, the tree may have more moisture in it than ovendry wood fiber, resulting in moisture contents greater than 100%. As wood is cut and exposed to air, the moisture dries from the wood. In a sawmill, this process can be expedited by running the rough lumber through a kiln process, exposing it to elevated temperatures to aid the drying process. Southern Pine lumber can be gradestamped as KD19 when it has been dried in a kiln to a maximum moisture content of 19%. This generally means that the average moisture content of the lumber will be close to 15%, with some pieces somewhat drier and some pieces somewhat wetter.
In the early 1990’s, new lumber design values were approved for all major softwood lumber species in North America. This testing program was known as the “In-Grade Testing Program” because each piece of lumber tested was required to be precisely of the grade being tested. The design values were based on tests of full-size pieces of lumber, which represented a significant departure from the previous basis for determining design values. For the In-Grade testing program, two grades (No.2 and SS) in three sizes (2×4, 2×8 and 2×10) were tested in three strength modes: bending, tension, and compression. Two new ASTM standards were written to specify the testing procedures (ASTM D4761) and the analysis procedures (ASTM D1990) to determine the new design values. Also included in ASTM D1990 was a paragraph stating that additional testing might be required if there was reason to believe that the resource had changed.
Continue reading “SPIB Resource Monitoring Program”
With the arrival of grade scanners in many southern pine production lines, there is a growing need to be much more precise with the planer machine work to plane a defect-free piece of lumber. Machine defects that the naked eye will miss on the production line, the scanners easily pick up and if only a .001” more than the parameters of the scanner the system may downgrade the piece or trim it off.
There are different ways of determining the grade of dimension lumber. Historically, “visual” grading is performed where a person looks at all four sides of a piece of lumber and evaluates the characteristics present to determine which of several visual grades the piece belongs. This grader works on a grading chain and quickly evaluates each piece of lumber.
In our previous BLOG, Shakes Checks and Splits in Dimension Lumber, we discussed the differences between these three types of defects or characteristics found in dimension lumber. All three are commonly thought of as different types of “cracks” or, “splits” in the wood. Each will have different limits in various grades depending on their effect on the strength and/or appearance for a particular stress rated or non-stress rated grades. There remains, however, some confusion between shakes and splits. After all, both shakes and splits create a longitudinal separation, or a “split”, in the wood, so what is the difference?
Recently, we shared a blog discussing the various types of lumber strength properties. These are important for engineers to use to design structure with wood. But where do the lumber design values come from? The process of determining lumber design values has evolved over the years. Continue reading “Determining Design Values for Lumber”
Wood has different strength properties when loaded in different manners. In fact, there are six main design values that are published for lumber and timbers in order for engineers to appropriately design a structure.
Bending: Two values are published for bending properties. The fiber stress in bending, Fb, is related to the breaking strength of a piece when loaded in bending. The Modulus of Elasticity, MOE, or E, is related to the stiffness of a piece loaded in bending. The stiffness is considered a “serviceability” factor and determines how much a piece bends as well as the magnitude of vibrations, say when someone walks across a floor. The following figure shows an example of a beam loaded with a bending load: