2001 ASD Supplements - unprotected PDF - American Wood Council

ASD STRUCTURAL GLUED LAMINATED TIMBER SUPPLEMENTGL-154.5 Preservative TreatmentTable 4.3Whenever practical, the moisture content of permanentstructural wood members should be kept below 20%.If this is not feasible then preservative treatment may berequired unless the heartwood of a naturally decay resistantspecies such as Redwood and Cedar is used.Most preservative chemicals used today do not significantlyalter the strength properties of structural woodproducts. However, the method of pre- and post-conditioning,as well as the treatment method itself, may weakenthe wood. For preservative treatment methods with AWPAaccepted manufacturing control, as listed in Table 4.3, theeffect on strength degradation of glulam can be eliminated.For more information concerning preservative treatmentof glulam, refer to APA Technical Note S580 or AITCStandard 109.Preservative Treatment Effect on Glued Laminated Timber4No adjustment is required when glued laminated timber is preservative-treated using the following AmericanWood Preservers’ Association StandardsDesignationTitleC1-98 All Timber Products - Preservative Treatment by Pressure ProcessesC14-98 Wood For Highway Construction - Preservative Treatment by Pressure ProcessesC15-98 Wood for Commercial - Residential Construction - Preservative Treatment by Pressure ProcessesC28-98 Standard for Preservative Treatment of Structural Glued Laminated Members and LaminationsBefore Gluing of Southern Pine, Coastal Douglas fir, Hem Fir, and Western Hemlock by PressureProcesses4.6 Fire Retardant TreatmentDESIGN ADJUSTMENT FACTORSEffects of fire retardant treatments on allowable designstresses shall be considered for wood products treatedwith pressure impregnated fire-retardants. However, theglued laminated timber industry does not recommend theuse of fire-retardant treatments with glued laminated timberand therefore, specific adjustment factors forfire-retardants used in conjunction with glued laminatedtimber shall be obtained from the company providing thetreatment services and the glulam manufacturer acceptsno responsibility for any structural glued laminated timberthat is fire retardant treated.4.7 Beam Stability Factor, C LAllowable bending stresses of glued laminated timbershall be adjusted by the beam stability factor, C L ,whenever applicable Refer to Section 3.3.3 of the NDSfor the determination of an appropriate beam stability factor.It is important to note that C L is not accumulative withthe volume factor, C v , given in Section 4.9 of this Supplementfor the design of structural glued laminated timber.4.8 Column Stability Factor, C PAllowable values for compression parallel to grainof glued laminated timber are affected by the dimensionsand modulus of elasticity. Refer to Section 3.7.1 of theNDS for the determination of an appropriate column stabilityfactor.APA – The Engineered Wood Association