【国外标准】 Standard Specification for Evaluation of Duration of Load and Creep Effects of Wood and Wood-Based Products

This specification covers the procedure for testing and evaluating duration of load and creep effects of wood and wood-based materials relative to an accepted duration of load adjustment model. This specification is proposed for use for products that are covered by a consensus standard such as lumber, structural composite lumber and structural use panels. The procedure covered in this specification, however, is not intended to evaluate performance of products under impact loading.1.1 This specification provides a procedure for testing and evaluating duration of load and creep effects of wood and wood-based materials relative to an accepted duration of load adjustment model. This specification was created for products that are currently covered by a consensus standard (for example, lumber, structural composite lumber, and structural-use panels). This procedure is intended to demonstrate the engineering equivalence to the duration of load and creep effects of visually graded lumber as specified in Practice D245 for a product under evaluation used in dry service conditions. This procedure is not intended to evaluate the performance of products under impact loading. Quantification of specific duration of load or creep factors is beyond the scope of this specification. For further guidance regarding the applicability of this specification refer to X1.1 in the Commentary.1.2 Use of the procedure in this specification to determine equivalence to the Practice D245 duration of load relationship is limited to solid wood and wood-based products whose long term load behavior is similar to that of solid wood. Equivalence demonstrated in this specification is dependent upon evaluation of a product's 90-day (minimum) creep-rupture performance. In this evaluation, three criteria must be satisfied: (1) adequate strength over a 90-day period, (2) decreasing creep rate, and (3) limited fractional deflection. A summary of the development of these criteria and the underlying assumptions behind them is provided in the Commentary in Appendix X1 and Appendix X2.1.3 Long term degradation phenomena not described by a creep-rupture model are not addressed in this specification (see Commentary X1.2.4).1.4 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.