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1、SECTIONTENWOODCONSTRUCTIONJohnBuddyShowalterAmericanForest&PaperAssociationWashington,D.C.ThomasG.WilliamsonAPATheEngineeredWoodAssociationTacoma,WashingtonWoodistheonlyrenewablesourceforbuildingmaterials.Itcomesfromforeststhatarecontinuallybeingreplantedastheyareharvested.Thispracticeensuresaplenti
2、fulsupplyofwoodforconstructionandforamyriadofotheruses.Comparedtootherbuildingmaterials,woodhasaveryhighratioofstrengthtoweight.Thismakesitveryeconomicalforuseinalltypesofconstruction.Woodalsohasanaestheticqualityandnaturalwarmthunequalledbyotherbuildingma-terials.Woodhasinherentcharacteristicswithw
3、hichconstructionusersshouldbefa-miliar.Forexample,asaconsequenceofitsbiologicalorigin,itisnonhomoge-neous.Also,propertiesofpiecesofwoodfromdifferentspeciesoftreemaybeconsiderablydifferent,andevenpropertiesofpiecesofwoodfromthesametreemaydiffer.Inthepast,determinationofengineeringpropertiesdependedhe
4、avilyonvisualinspection,keyedtoaverages,ofwoodpieces.Research,however,hasmadepossiblebetterestimatesoftheseproperties.Itisnolongernecessarytorelysoheavilyonvisualinspection.Greateraccuracyindeterminationofengineeringpropertieshasbeenmadepossiblebymechanicalgradingprocedures.Improvementsinadhesivesfo
5、rwoodalsohavecontributedtothebettermentofwoodconstruction.Theseadvancesinadhesiontechnologycombinedwithadesiretoutilizemoreefficientlyavailablewood-fiberresourceshaveledtoincreasinguseofsuchproductsasorientedstrandboard(OSB),glued-laminatedtimber(glulam),woodIjoists,andstructuralcompositelumber(SCL).1
6、0.1BASICCHARACTERISTICSOFWOODWooddiffersinseveralsignificantwaysfromotherbuildingmaterials.Itscellularstructureisresponsible,toaconsiderabledegree,forthesedifferences.Becauseof10.1TABLE10.1ShrinkageValuesofWoodBasedonDimensionsWhenGreenDriedto20%MC*Driedto6%MC†Driedto0%MCRadial,Tangential,Volumetric,
7、Radial,Tangential,Volumetric,Radial,Tangential,Volumetric,Species%%%%%%%%%Softwood:‡Cedar:Alaska0.92.03.12.24.87.42.86.09.2Incense1.11.72.52.64.26.13.35.27.6PortOrford1.52.33.43.75.58.14.66.910.1Weste
