Preliminary Analysis Suggests Smaller Reductions than Originally Projected
The latest full In-Grade Testing matrix for visually graded Southern Pine dimension lumber has been completed by the Southern Pine Inspection Bureau (SPIB) in cooperation with Timber Products Inspection and others. In a two-step process, more than 7,400 full-size samples of commercially-produced Southern Pine were destructively tested. As the first step, No.2 2x4s were tested which resulted in new design values for Southern Pine sized 2” to 4” wide and 2” to 4” thick in No.2 Dense and lower grades on an interim basis; new design values for only those sizes and grades became effective June 1, 2012, pending the potential for slight adjustments based on results from additional testing in step two.
As the second step, Select Structural (SS) 2x4s, No.2 and SS 2x8s, and No.2 and SS 2x10s were tested to complete the full In-Grade Testing matrix. SPIB and Timber Products collected the test specimens according to a sampling plan approved by the American Lumber Standard Committee Board of Review (ALSC BOR). Destructive tests in bending, tension and compression were then conducted while gathering stiffness and other property data, all in accordance with ASTM International standards. Throughout the entire process, technical oversight was provided by the USDA Forest Products Laboratory.
As a rules-writing agency, SPIB must also follow a rigorous approval process to establish new design values for all sizes and grades of visually graded Southern Pine dimension lumber. SPIB began the approval process by performing a preliminary analysis of the complete In-Grade Testing data in conformance with consensus standard ASTM D1990, Standard Practice for Establishing Allowable Properties for Visually-Graded Dimension Lumber from In-Grade Tests of Full-Size Specimens.
The SPIB Technical Committee met on July 18-19, 2012 to review the test data and the preliminary data analysis of the full In-Grade Testing matrix. This committee includes technical representatives of lumber producers, general interest and key user groups, such as home builders and component manufacturers. The preliminary data analysis suggests smaller reductions for the wider widths and higher grades as compared to the No.2 2x4s, and even some small increases as compared to current design values. While it is too early in the approval process to present proposed design values, generalized ranges of potential change for the wider widths and higher grades are provided in Table 1.
Table 1 – Approximate Design Value Changes* for Southern Pine 2x6s through 2x12s (all visual grades) and 2x4s (SS and No.1)
|Property||Approximate Design Value Changes*|
|Compression Perpendicular||No change|
|Bending||-15% to -25%|
|Tension||-150 psi to +50 psi|
|Modulus of Elasticity||-100,000 psi to No change|
The preliminary data analysis of the full In-Grade Testing matrix combines all data from steps one and two to provide the best estimates of design values. This analysis suggests upward revisions to some of the design values that became effective June 1, 2012 based only on No.2 2×4 test data. Table 2 provides potential adjustments to the June 1 design values for Southern Pine sized 2” to 4” wide and 2” to 4” thick in No.2 Dense and lower grades.
Table 2 – Approximate Design Value Adjustments* for Southern Pine 2x4s (No.2 and lower grades)
|Property||Approximate Design Value Changes*|
|Modulus of Elasticity||No change to +100,000 psi|
|Bending||+25 psi to +50 psi|
The SPIB Technical Committee made the following recommendations to the SPIB Board of Governors, the next step in the approval process, based on the preliminary data analysis following ASTM D1990:
- Approval of all new design values for visually graded Southern Pine lumber, including Dense and NonDense grades
- No change in the current Southern Pine specific gravity value of 0.55
- Prime grades (No.1 Prime and No.2 Prime) continue to have the same design values as their corresponding dimension lumber grades
Potential Timeline for Next Steps:
- August, 2012 – SPIB Board of Governors meeting to approve proposed design values. The SPIB Board of Governors considers recommendations from the SPIB Technical Committee and other pertinent information before making a final determination.
- September, 2012 – SPIB submittal of proposed design values to the ALSC BOR. The Forest Products Laboratory will review the data, calculations, and resulting proposed design values to ensure conformance with ASTM D1990.
- October 18, 2012 – ALSC BOR meeting to hear testimony from interested parties. The ALSC BOR considers all input before making a final decision.
- Date To Be Determined – Effective date for new design values for all grades and sizes of visually graded Southern Pine dimension lumber. The ALSC BOR evaluates each case individually, so the exact recommended effective data is unknown at this time. In the case of the proposed Southern Pine design values based on only No.2 2×4 tests, the ALSC BOR ruled in January 2012 with a recommended effective date of June 1, 2012, providing six months for an orderly transition.
Southern Pine remains strong, dependable
“This preliminary analysis delivers positive results for Southern Pine lumber producers and their customers,” says Cathy Kaake, SFPA’s vice president of technical marketing. “For example, with no change to its specific gravity, Southern Pine retains its superior fastener and connector-holding ability, and that’s good news for component manufacturers and other users,” Cathy adds.
SFPA continues to support an orderly transition to new design values. Since October of last year, SFPA has facilitated discussions among producers, component manufacturers, treaters, builders, dealers and other customer groups. Those efforts helped form a united consensus that a transition period would prove beneficial. By June 1, many businesses had transitioned to the new values with minimal disruptions to their operations. “Moving forward, SFPA and allied groups will encourage the ALSC Board of Review to once again recommend a six-month transition period after certification of new design values for all grades and sizes,” says Cathy.
Southern Pine remains comparable to other softwood species used in residential and commercial construction. Southern Pine is the most-tested lumber species and will be monitored with annual destructive testing.
BACKGROUND: The last major change for visually graded dimension lumber occurred in 1991 when design values for Southern Pine and other North American species were published based on In-Grade testing of full-size samples of commercially produced lumber. Since 1994, SPIB has conducted an annual resource monitoring program developed in collaboration with the U.S. Forest Products Laboratory (FPL). SPIB is the first rules-writing agency to publish new design values. Rules-writing agencies responsible for other species are in different stages for evaluating design values.
SFPA does not test lumber or establish design values. SFPA’s primary function is to market lumber products and to help users understand Southern Pine grading rules and design values.