1996 LRFD Manual for Engineered Wood Construction

GUIDELINELRFD MANUALTO LRFDFORFORENGINEEREDSTRUCTURALWOODCOMPOSITECONSTRUCTIONLUMBER 9This manual was developed with the intent of coveringall structural applications of wood-based products andtheir connections that meet the requirements of the referencedstandards. Other primary referenced standards are:ASCE 7-93, Minimum Design Loads for Buildings andOther Structures: This standard is the basic reference forload factors and load combinations that should be checkedin design of buildings and other structures. Use of therequirements in this standard for applications other thanbuildings (and the other special structures that it covers)is beyond the scope of ASCE 7-93.For example, ASCE 7-93 provides no guidance onthe appropriate load factors to design a bridge, or on theproper load combinations to check. The same difficultyarises when designing a scaffold or a concrete form system— neither of these applications have loading criteriathat have been derived in a manner consistent withASCE 7.ASTM D5457-93, Standard Specification for Computingthe Reference Resistance of Wood-based Materials andStructural Connections for Load and Resistance FactorDesign: This specification provides the link betweenmaterial specifications or product manufacturing standardsand LRFD reference resistance values. This ASTM specificationdefines two alternative routes for deriving designvalues:• Format conversion: Code-accepted ASD values arepermitted to form the basis for conversion into referenceresistance values. Conversion factors have beenchosen such that designs retain roughly the same levelof safety as found in ASD. Format conversion facsoluble,making fire-retardant treatments unadaptable toweather exposure. Impregnated fire retardants that areresistant to both high humidity and exterior exposures arebecoming increasingly available on the market for treatedlumber and plywood products. See product-specific recommendationsregarding proper procedures forpreservative treatment of that product.11.4 Products Covered in This Manualtors are addressed in ASTM D5457 and are discussedfurther in the product supplement and guideline documents.• Reliability-based conversion: ASTM D5457 providesprocedures for deriving LRFD reference resistancevalues directly from test data.1.4.1 Products IncludedDesign information for LRFD is available for productsin the following list. The designation of Supplementindicates a document that contains a complete set of designvalues plus other information for use with this manualand AF&PA/ASCE 16-95. The designation of Guidelineindicates a document that does not contain design values,but includes other information required to design the productsusing LRFD.Supplements• Structural Lumber Supplement• Structural Glued Laminated Timber Supplement• Timber Pole and Pile Supplement• Structural-Use Panel Supplement• Structural Connections SupplementGuidelines• Metal Plate Connected Wood Truss Guideline• Wood I-Joist Guideline• Structural Composite Lumber Guideline• Pre-engineered Metal Connectors GuidelineINTRODUCTIONAMERICAN FOREST & PAPER ASSOCIATION