ASTM WK66306

    Revision of D1990 - 16 Standard Practice for Establishing Allowable Properties for Visually-Graded Dimension Lumber from In-Grade Tests of Full-Size Specimens

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    Active Standard: D1990 - 16

    Developed by Subcommittee: D07.02 | Committee D07 | Contact Staff Manager



    WK66306


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    Rationale

    D1990 requires that a Grade Quality Check be performed to ensure that the tested sample adequately represents the intended grade. This GQI check involves using the knots present in the failed cross-section and calculating the corresponding strength ratio using the equations specified in ASTM D245. The fifth percentile of failed pieces for which a strength ratio can be calculated must be sufficiently low enough to be considered representative of the grade. If a sample has too high of a GQI, the test values must be supplemented with more data or adjusted downward to reflect the assigned GQI for the grade. The strength ratio equations in D245 were developed so users could determine what allowable knots could be permitted in a specific grade to maintain a certain strength ratio. There are various equations for differing strength properties and differing locations of knots. For example knots in the center of the wide face are less detrimental to strength in bending than knots found on the edge of the wide face. For compression strength, the knot location is not critical, so the compression strength ratio equations permit larger knots anywhere in the piece. This makes perfect sense for how D245 was intended to be used. A problem has arisen though when using the D245 strength ratio equations to determine if a sample is representative of on grade material in the context of design value assignment in D1990. If a piece is on grade using the bending strength ratio equations, the calculated GQI for that piece could be much higher when using the compression strength ratio equation. This would necessitate a significant reduction in compression strength data to force the compression GQI to be within on-grade acceptable limits. If a piece had a knot large enough to be considered a maximum size knot using the compression equation, it would be significantly below grade when considered with the bending equations. To remedy this situation, it is proposed that the same strength ratio equations be used for all properties when evaluating the GQI and the Grade Quality Check for sample acceptance in D1990. The following change to ASTM D1990 Note 4 is proposed to address this anomaly:

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    Work Item Status

    Date Initiated:
    12-18-2018

    Technical Contact:
    Christopher Senalik

    Item:
    008

    Ballot:
    D07 (19-02)

    Status:
    Negative Votes Need Resolution