A General Introduction to Wood Construction Journal of Architectural Education … An Exploration of the Relationships between Houses and Forests in American History … William Gould Sturges … University of Oregon There is a Supply & Demand Imbalance for Wood Products … In 1986 we consumed 57.2 Billion Board Feet (bbf) of Wood Products, yet only 70% was Produced Domestically … This is 40% greater Consumption than in the 50's and 60's … The Trend is Getting More Acute … In 2040, the estimates are >70bbf Forests … Provide: … species habitat … watershed protection … biological gene banks … medicine i.e.. taxol Primeval Forests: 1620 Primeval Forests: 1850 Primeval Forests: 1989 Population Density Maps: 1776, 1876, 1976 Annual Housing Unit Production Year Housing Units <1940 800,000 1950 2,000,000 1973 3,000,000 1992 1,100,000 Iroquois Longhouse Iroquois Longhouse … Minimal Impact on the Forest … High Density Configuration … Same Quantity of Wood as Today’s SF Detached BUT... … they housed 50 - 60 people compared to today's average family of 2.5 persons Log Cabin Log Cabin … First Response to Housing Need … Forests were Viewed as an Impediment to Agriculture … 9216 in3/lf Timber Framing Timber Framing … Coincided with the Development of Sawmills … Maine ca. 1620 … Water Powered … Mortise and Tenon … Labor Intensive … 6210 in3/lf Balloon Framing Balloon Framing … Coincided … Steam with the Development of: Powered Sawmills … Machine Made Nail … 4234 in3/lf Western Platform Framing Western Platform Framing … Coincided with the Development of Veneer Panel Products … early … 1368 1900's in3/lf Wood Use per Lineal Ft of 8' High Wall Housing Type Cubic Inch / LF Material Savings Log Cabin 9216 0% Timber Frame 6210 33% Balloon Frame 4234 46% Platform Frame 1368 85% Source: Jerry Finrow, The Conflict between Dwelling and the American Forest. A Revolution in Basic Cultural Values Energy Consumption* of Common Building Materials MJ/kg Concrete 2** Lumber 4~7 Plywood 18 Steel 25~35 * Mining, Processing, and Transporting Combined ** Concrete Contributes 3% of Greenhouse Gases Strategies for the Future … Sustainable Forests … Create Housing with Less Demand Sustainable Forest Farming … Forest Stewardship Council (FSC) … Limit Timber Removal to Prevent Decline in Quality/Quantity … Provide Variety of Ages … Allow Trees to Mature Fully … Maintain Plant and Animal Habitat … Protect the Soil Create Housing w/ Less Demand … Recycle … Don't Over-design … Engineered Wood Products … Higher Density Configurations Wood Construction Topics … Wood Botany … Lumber … Panels Products … Engineered Wood Products Tree Structure … Bark … Cambium Layer … Sapwood - conduction, storage and support … Heartwood - support only … Growth (Annual) Rings … Late Wood - summer/fall, small, densely packed cells … Early Wood - spring, large cells Cross Section through a Tree Wood Botany … Two Major Groups … Coniferous … Deciduous Coniferous … Softwoods (not a measure of hardness) … Gymnosperms - naked seeds … Evergreen e.g. Douglas fir, larch, pine … Narrow leaf … Coniferous trees lack vessels Deciduous … Hardwoods (not a measure of hardness) … Angiosperms - covered seeds … Shed leaves annually … Broadleaf e.g. oak, maple, cherry … Deciduous trees have vessels for support and conduction of nutrients Wood is Anisotropic … An anisotropic material has physical properties that are different with respect to their three major orthogonal planes Three Major Planes … Longitudinal - along the length of the log … Radial - with respect to the center of the log … Tangential - with respect to the growth rings Wood is Hygroscopic … An hygroscopic material has an affinity for water molecules which causes swelling and shrinking as the material reaches equilibrium with its environment Wood is Viscoelastic … enough is enough! Moisture Content … the weight of water as a percentage of the weight of an oven dry sample of wood … freshly cut lumber can range from 30% to200% Fiber Saturation Point … the point at which the cell cavities are empty but the cell walls are full of water … approx. 28% MC Moisture Content Wood Product Moisture Content Shrinkage Relative to the Major Planes Manufacture of Sawn Lumber Surfacing … S4S, surfaced four sides … S-Green, surfaced at >19% MC … S-Dry, surfaced at 19% or less Categories of Dimension / Stress Rated Framing Lumber How Do We Determine the Strength of Lumber Visual Grading by Certified Graders … based upon tested strength of clear sample … reductions in strength (grade) made based upon defects, grain direction etc Grade Stamps Machine Testing … every board is tested and stamped according to results Machine Stress Rated Lumber In-Grade Testing … North American In-Grade Testing Program, 1977 … testing of 70,000 full size pieces (1 million board feet) … created a database of empirical design values … Bending values went up for narrows and high grades, down for wides and lower grades Engineered Wood Products Engineered Wood Products … attempt to improve the basic properties of lumber … strength … appearance … dimensional stability … cost … use fast-growing, low-density wood species in combination with plastic resins Engineered Wood Products … potential disadvantages … out-gassing from formaldehydes … deterioration under certain conditions … FRT plywood … appearance Engineered Wood Products … Sheathing and Decking … Main Structural Members … Stress Skin Foam Panels Sheathing and Decking … Plywood … Oriented Strand Board (OSB) and Waferboard Main Structural Members … Light Frame Trusses … Glue Laminated Lumber (Glulam) … Laminated Veneer Lumber (LVL) … Parallel Strand Lumber (PSL) … Prefabricated Wood I-Joists Light Frame Trusses … Flat Plate Connectors … Stamped metal plates hydraulically pressed into wood to make connections … Suitable for floors and roofs … Proprietary Connectors … Wood Top and Bottom Chord … Fab. Steel Element for Web w/ Integral Fastener … Split Ring Connector … For Custom-Designed, Field-Fabricated Trusses … Increase Effective Area of Joint Glue Laminated Lumber (Glulam) … Old Technology … Headers, Beams, Girders and Columns … Strength Depends on Wood Species and Quality … Limitless Variety of Straight and Curved Configurations Glulam Manufacture Laminated Veneer Lumber (LVL) … Based on Plywood Technology … Headers, Beams and Girders … Sized to Flush Frame with Platform Framing … i.e. … Fb 1 3/4" x 9 1/4" = 2800 psi, E= 2,000,000 psi LVL Manufacture Parallel Strand Lumber (PSL) … Based on Cross between Plywood & OSB Technology … Strands are up to 8' long and 1/2" thick … Headers, Beams, Girders and Columns … Sized to Flush Frame with Platform Framing … i.e. 1 3/4" x 9 1/4" … Potential Applications Work in Finish and Cabinet PSL Manufacture Prefabricated Wood I-Joists … Profile Similar to Steel Beams … Top and Bottom Flanges Resist Compressive and Tensile Stresses Respectively … Solid Wood … LVL … Glulam … Web Resists Shear Forces … Plywood … OSB Stress Skin Foam Panels … Walls, Floors and Roofs … Foam Core Bonded to Structural Skin … Modular Design Principles … Joints between Panel Are Key to Usability Joint Types … Dual Spline e.g. R-Control … Special Piece e.g. Ray-Core … Stud … Cam Lock