Wood Engineering Materials PDF

2024-03-18 CIVI 321 ENGINEERING MATERIALS WOOD A.M. Soliman, PhD, P.Eng Associate Professor Department of Building, Civil & Environmental Engineering (BCEE) 1 Introduction Wood is the earliest construction material used by mankind. 300 Years Old Multi-Dome Church 2 1 2024-03-18 Introduction Wood is...

2024-03-18 CIVI 321 ENGINEERING MATERIALS WOOD A.M. Soliman, PhD, P.Eng Associate Professor Department of Building, Civil & Environmental Engineering (BCEE) 1 Introduction Wood is the earliest construction material used by mankind. 300 Years Old Multi-Dome Church 2 1 2024-03-18 Introduction Wood is the earliest construction material used by mankind. 3 WHY DO WE USE WOOD? 4 2 2024-03-18 Introduction Wood is the earliest construction material used by mankind. Easy to use Durable High strength Low weight Widely available Low cost 5 Introduction Still very widely used today for: Building frames Bridges Utility poles Floors Roofs Trusses Piles, etc. 6 3 2024-03-18 WHAT ARE TYPES OF WOOD? 7 8 4 2024-03-18 Classification of Trees Endogenous (intertwined growth) Trees that grow inwards in a longitudinal fibrous mass  Very strong, flexible and lightweight  Not generally used for engineering applications. The new wood-strands being interspersed among the old, and causing cross-surfaces to appear dotted. palm trees 9 Classification of Trees Exogenous (outward growth): Fibers grow from the center outward by adding concentric layers (annual rings) which gives more predictable engineering properties. Deciduous (broad leaf) Hardwood (ash, oak, maple) Expensive slow growing Coniferous (cone bearing) Softwood (fir, pine, spruce) 10 5 2024-03-18 11 12 6 2024-03-18 Main Structural Features of Tree Stem From center axis outwards:  Pith – center stem  Heartwood (darker) – provides structural support  Sapwood (lighter) – transports the sap (vascular tissue)  Cambium (very thin layer) – location of wood growth  Inner bark  Outer bark 13 Structure of Wood Each annual ring of exogenous tree is composed of: – Earlywood (light ring): rapid spring growth of hollow thinwalled cells – Latewood (dark ring): dense summer growth of thickwalled cells which are much harder & stronger Earlywood Latewood 14 7 2024-03-18 HeartWood Early Wood Inner Bark Late Wood Outer Bark SapWood Cambium 15 Chemical Composition 3 2 1 16 8 2024-03-18 Chemical Composition 2 Hemicellulose 1 Cellulose (40-50% by weight) Polymer that forms strands that make up cell walls (wood fibers) High density indicates higher strength (Gcellulose = 1.5)  15-20% of softwood  20-30% of hardwood A mix of Polymers (lower strength) 3 Lignin (Glue)  23-33% of softwood  16-25% of hardwood 4 Others Extractives 5-30% by weight (coloring matters, fats, resins, waxes, starches Ash-forming (minerals) 0.1-3% by weight (calcium, potassium, phosphate, silica) 17 Wood is Anisotropic (properties change with direction) 1.Longitudinal  Parallel to the long axis (grain)  Strongest and least shrinkage 2.Radial  Perpendicular to the growth rings (out from center) 3.Tangential  Tangent to the growth rings  Weakest and most shrinkage Directions influence strength, modulus, thermal expansion, conductivity, shrinkage, etc. 18 9 2024-03-18 Moisture Content 19 Moisture Content The moisture content of wood is directly related to the humidity and temperature of the surrounding air. Shrinkage, Strength, & weight depend on moisture content 20 10 2024-03-18 Moisture Content Equilibrium Moisture Content (EMC): occurs when the wood has reached a water content equilibrium with its environment and is no longer gaining or losing moisture. As wood absorbs or bleeds moisture, it will expand or contract. The more moisture that is absorbed or displaced, the more severe the expansion/contraction of the wood product. 21 Fiber Saturation Point (FSP) Moisture content when cells are completely saturated with bound water but no free water inside cell cavities FSP = 21-32%.  Above FSP: Changes affect only wet weight  Below FSP: small changes strongly affect all physical and mechanical properties Free water inside cell cavities doesn't affect shrinkage Bound water, wood shrinks on removal 22 11 2024-03-18 Shrinkage  Largest shrinkage is in the tangential direction  Smallest shrinkage is in the longitudinal direction  zero shrinkage above FSP regardless of direction 23 Because of the difference in tangential and radial movement, boards change shape as they expand and contract. The way in which they change depends on how they are cut from the tree.* 24 12 2024-03-18 25 Wood Production Production Steps: 1. Harvesting 2. Sawing 3. Seasoning (drying) 4. Surfacing (Planing) (optional) 5. Grading 6. Preservative Treating (optional) 26 13 2024-03-18 1 Harvesting 2 Sawing 3 Surfacing optional 5 Grading 4 Seasoning (drying) optional Cutting Treating 27 Wood Products for Construction 28 14 2024-03-18 Wood Products for Construction 29 Wood Products for Construction Dimensional lumber – 2” to 5" thick – 2x4’ etc. -Used for light framing – studs, joists, beams, rafters, trusses, decking 30 15 2024-03-18 Wood Products for Construction Heavy timber – 4x6, 6x6, 8x8 and larger - usually rough sawn (actual sizes) - used for heavy framing, railroad ties, landscaping 31 Wood Products for Construction Round stock posts and poles – used for marine piling, utility poles, etc. utility poles marine piling 32 16 2024-03-18 Sawing 33 Sawing  Live (plain) sawing – most rapid and economic  Quarter sawing – maximum amount of prime (vertical) cuts  Combination – most typical 34 17 2024-03-18 Three types of board cut Flat-sawn (grain is