Standard Practice for Establishing Clear Wood Strength Values
This practice presents the two standard methods for determining the strength values of clear wood of different species in the unseasoned condition, unadjusted for end use, applicable to the establishment of working stresses for different solid wood products such as lumber, laminated wood, plywood, and round timbers. Method A provides for the use of the results of surveys of wood density involving extensive sampling of forest trees, in combination with the data obtained from standard strength tests. The average strength properties are obtained from wood density survey data through linear regression equations establishing the relation of specific gravity to the several strength properties. Method B, on the other hand, provides for the establishment of tables of strength values based on standard tests of small clear specimens in the unseasoned condition for use when data from density surveys are not available. Separate tables are employed to present the data on woods grown in the United States and on woods grown in Canada. Guidelines for the interpretation of the data in terms of assigned values, information basic to the translation of the clear wood values into working stresses, presently available data with appropriate provisions for their application and use, and methods for estimating some useful mechanical properties by relating them to other properties are presented herein as well.
1.1 This practice covers the determination of strength values for clear wood of different species in the unseasoned condition, unadjusted for end use, applicable to the establishment of design values for different solid wood products such as lumber, laminated wood, plywood, and round timbers. Presented are:
1.1.1 Procedures by which test values obtained on small clear specimens may be combined with density data from extensive forest surveys to make them more representative,
1.1.2 Guidelines for the interpretation of the data in terms of assigned values for combinations of species or regional divisions within a species to meet special marketing needs, and
1.1.3 Information basic to the translation of the clear wood values into design values for different solid wood products for different end uses.
1.1.4 For species where density survey data are not as yet available for the re-evaluation of average strength properties, the presently available data from tests made under the sampling methods and procedures of Test Methods D143 or Practice E105 are provided with appropriate provision for their application and use. Because of the comprehensive manner in which the density survey is undertaken, it follows that the re-evaluated strength data are intended to be representative of the forest stand, or rather large forest subdivisions.
1.1.5 Some useful mechanical properties (tensile strengths parallel and perpendicular to grain, modulus of rigidity for a longitudinal-transverse plane, and transverse modulus of elasticity) have not been extensively evaluated. Methods are described for estimating these properties by their relation to other properties.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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