2001 ASD Supplements - unprotected PDF - American Wood Council

SP-20DESIGN ADJUSTMENT FACTORS4.1 GeneralPanel design capacities are determined by multiplyingbaseline capacities, as given in Tables 3.1 through 3.4,by the adjustment factors in NDS Section 9.3.Tabulated capacities provided in this Supplement aresuitable for reference end-use conditions. Reference enduseconditions are consistent with conditions typicallyassociated with light-frame construction. For wood structuralpanels, these typical conditions involve the use offull-sized untreated panels in moderate temperature andmoisture exposures.Appropriate adjustment factors are provided for applicationsin which the conditions of use are inconsistentwith reference conditions. In addition to temperature andmoisture, this includes consideration of panel treatmentand size effects. Reference conditions and adjustment factorsare provided in Sections 4.2 through 4.9.The tabulated adjustment factors are applicable foruse with capacities of wood structural panels.4.2 Grade and Construction Factor, C GAdjustments to wood structural panel design valuesfor grade and construction and panel size, shall be in accordancewith NDS Section 9.3.4. Reference capacitiespresented in Tables 3.1 through 3.4 of this Supplementrepresent minimum values for each listed grade and construction.Tables 3.1.1, 3.2.1, 3.3.1, and 3.4.1 provideadjustments to the minimum capacities as appropriate forspecific constructions and grades. These Tables are locatedclose to the capacity tables for convenience. To takeadvantage of these, the specifier must insure that the correctpanel is used in the final construction.4.3 Load Duration Factor, C DDesign capacities listed are based on normal loadduration. Adjustment factors for strength capacities shallbe based on NDS Section 9.3.2 (see Table 4.2).Table 4.2Frequently Used LoadDuration Factors, C D1Load Duration C D Typical Design LoadsPermanent 0.9 Dead LoadTen years 1.0 Occupancy Live LoadTwo months 1.15 Snow LoadSeven days 1.25 Construction LoadTen minutes 1.6 Wind/Earthquake LoadImpact 2 2.0 Impact Load1. Load duration factors shall not apply to modulus of elasticity, E, nor tocompression perpendicular to grain design values, F c⊥ , based on a deformationlimit.2. Load duration factors greater than 1.6 shall not apply to structural memberspressure-treated with water-borne preservatives, or fire retardant chemicalsand are not recommended for wood structural panels. The impact loadduration factor shall not apply to connections.APA – The Engineered Wood Association