Slide 1In This Unit…Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Diagram of cellular structure of woodAlong grain & cross grainWood ProductionStep 1. HarvestingSlide 14Slide 15Drying processSlide 17SurfacingSlide 19Slide 20Stamped lumberGrade stampsSlide 23Organisms that Degrade WoodDeterioration of WoodSlide 26Classification of softwood lumberGrades of Dimension LumberBoard foot measureProblemSlide 31Slide 32Slide 33Slide 34Slide 35Slide 36Glued Laminated WoodSlide 38Slide 39Slide 40Slide 41Slide 42TrussesI-JoistsPanel ComponentsFactory-Built HousingLecture 10: WoodKamalesh Panthi, Ph.D.Department of Construction ManagementEast Carolina UniversityCMGT 2210 - Construction & Civil MaterialsIn This Unit…IntroductionStructure & Properties of WoodWood ProductionGrades Preservation Quantity EstimationWood ConnectionManufactured Wood ProductsClassification of TreesSoftwoodsHardwoodsPineFirWalnutRed OakClassification of TreesSoftwoodsHardwoods•From cone-bearing (coniferous) trees•Relatively simple cell structure•Generally, plain figure (pattern of grain and surface features)•From broadleafed (deciduous) trees•More complex cell structure•Often more interesting figure•Mostly originating from North American forests•Fast-growing, plentiful, relatively inexpensive•Generally soft, easily worked•Uses:•structural wood products •finish trim, shingles and siding•flooring•But not all softwoods are soft. For example, Douglas Fir is harder than some hardwoods.•Harvested from around the world•Slower growing, generally more expensive than softwoods•Denser, with greater variety of colors and figure•fine trim, paneling•flooring•fine cabinet work, furnitureSoftwoodsHardwoods•Each annual ring of exogenous tree is composed of:•Earlywood (light ring): rapid spring growth of hollow thin-walled cells•Latewood (dark ring): dense summer growth of thick-walled cells which are much harder & stronger8Structure of WoodWood is Anisotropic•Longitudinal•parallel to the long axis (grain)•strongest and least shrinkage•Radial•perpendicular to the growth rings (out from center)•Tangential•tangent to the growth rings•weakest and most shrinkage•Directions influence strength, modulus, thermal expansion, conductivity, shrinkage, etc. 9- properties change with direction:Diagram of cellular structure of woodAlong grain & cross grainWood ProductionProduction Steps:1. Harvesting2. Sawing3. Seasoning (drying)4. Surfacing (Planing) (optional)5. Grading6. Preservative Treating (optional)12Step 1. Harvesting•Minimal sap•Concerns of fire hazard•Other plant growth and underbrush is minimal13Step 2. Sawing14•Plainsawn: Lumber cut tangent to the annual ring (right)•Plainsawn for hardwoods•Flat sawn for softwoods•Quartersawn: Lumber cut radially to the annual rings (left)•Quartersawn for hardwoods•Plainsawn for softwoods•Green wood has 30-200% moisture content•~15% when it leaves the mill•Methods of Seasoning•air drying (cheap & slow)•kiln drying (fast & expensive)•usually a combination•As wood dries below approximately 30 percent MC, it shrinks, mostly in cross section, and only slightly in length.•Difference between rates of tangential and radial shrinkage cause distortions in shape, especially in flatsawn lumber. Step 3. Seasoning (Drying)15•Cavity water (free water)•Bound water (cell-wall water)•FSP (fiber saturation point occurs when cavity water has all evaporated, and bound water has just begun to evaporate•Average FSP is 30%•Wood begins to shrink as bound water evaporates from cells•Lumber is considered to be “green”•Lumber may become stiffer and stronger as it becomes more dryDrying process•Surfacing takes 1/4" (or more) from each side•S4S = surfaced 4 sides = “dressed”•Nominal sizes refer to the rough-sawn (unsurfaced) dimensions of the lumber in inches•For example, the actual dimensions of a 2 x 4 are 1 ½ in. x 3 ½ in.•S-DRY- surfaced after seasoned•S-GRN- surfaced when greenStep 4. Surfacing (Planing)17SurfacingLumber Grades (Step 5)19Visual grading •Each member is viewed on all four surfaces•Based on grading rules that relate primarily to growth characteristics (7 recognized agencies in US & Canada)•Inspections conducted by independent agency•Each piece of lumber stamped with•Species•Moisture content at time of surfacing•Mill that produced the piece•Inspection agency•Structural gradeVisual grading or Machine GradingStamped lumberGrade stampsMSR Grade stampNote stamp provides values for E modulus of elasticity , and Fb bending stressOrganisms that Degrade WoodFungi caused dry rotSpruce Ips Beetle Bacteria damageblack heartwood Termite damage Marine-borer damage to a buried pile 24Deterioration of WoodCauses•Insects•Fungi•Wood Borers•FireProtection•Chemical Treatments•Isolate Moisture•Protected Construction•Fire RetardantsChapter 10: WoodWood Preservation1.Water-borne (Arsenic)2.Oil-borne (Penta-chlorophenol- but toxic)3.Creosote and solutions containing creosoteApplication Techniques•Superficial treatment: generally not effective•Liquid penetration (pressure treating at high temp., heat, & moisture)Structural members need to be fabricated as much as possible before treatment in order not to expose untreated wood by cutting, drilling holes, etc.If not possible, treat cuts and holes with a liberal application of field applied preservative 26Classification of softwood lumberGrades of Dimension LumberBoard foot measureAssume:2 x 12 piece of lumber20 long= 40 board feetNote: nominal dimensions are usedPrice of lumber is quoted in terms of 1000 bd ft (MBF)ProblemHow much will a builder pay for: 900 pieces of 2x12 lumber each 16ft long If the price of lumber is $800 MBF(16 x 2 x 12)(900)(12)= 28,800 bd ft = 28.8 MBFTotal volume of lumber =28.8 MBF ($800) = $23,040WOOD FASTENERSNails•Inexpensive, fast and easy to install•Sized in pennies (d), e.g.:•16d: 3½"; 8d: 2½"; 2d: 1"•Materials:•bright (plain steel)•galvanized (zinc-coated for corrosion resistance)•stainless steel•aluminum, copper, etc.•Many shapes for different uses•May be driven by hand or nail gunScrews & Bolts•Greater holding power than nails •More expensive and time-consuming to install•Bolts require pre-drilled holes. •Some screws require pilot holes, some are self-drilling.•Great variety of shapes, sizes, head styles, driver shapes•Toothed