Timber PDF

` TIMBER  LEARNING OUTCOMES  Explain what is meant by timber and lumber.  Explain and describe the characteristics of timber.  Discuss the moisture content of timber.  Discuss the manufacturing process of timber.  Discuss and explain the types of timber....

` TIMBER  LEARNING OUTCOMES  Explain what is meant by timber and lumber.  Explain and describe the characteristics of timber.  Discuss the moisture content of timber.  Discuss the manufacturing process of timber.  Discuss and explain the types of timber.  INTRODUCTION  Wood is an organic matter obtained from trees.  Wood is made-up primary of cellulose.  Wood which is suitable or fit for engineering construction or engineering purpose is called “timber”.  Timber was derived from an English word “timbrian”  North America:  Wood that has been processed by a mill for construction is known as “lumber”.  Unprocessed wood or standing tree trunks known as timber.  TIMBER CHARACTERISTICS  Properties:  It is fibrous and elastic.  Performs better under tension than compression.  Undergoes varying degrees of moisture movement  Straight-grain is stronger than irregular grain and it is easier to work with.  TIMBER CHARACTERISITCS  Trees are divided into two classes:  Hardwood  Softwood  Hardwood:  They have broad leaves, which they shed annually. Hardwood Trees https://www.treehugger.com/identification-of-the-most-common-  The specific gravity ranges from about 0.15 to more than hardwoods-1341843 1.0 for some dense species.  High strength and durability and varies with colour.  More expensive than softwood  Softwood:  They have needle-like or scale-like leaves, which they shed when damaged or unused.  The specific gravity of softwood ranges from about 0.25 to 0.65. Softwood Trees https://www.coniferousforest.com/plants-trees  Used for most structural timber since it is easy to work with due to its softness and grain straightness TIMBER CHARACTERISTICS  Trees grow by adding new layers of cells to the outside of the sapwood  The sapwood store nutrients and support the tree.  The inner layers of the sapwood stop storing nutrients and becomes heartwood, which ONLY supports the tree.  In some species heartwood is more resistant to decay.  No difference between the specific gravity of sapwood and heartwood.  Fast growing cells are known as earlywood/springwood. Cross Section of Tree Stem Su, Pingping (2012)  Slower growth are called latewood/summerwood.  Latewood is denser and stronger than earlywood.  TIMBER CHARACTERISTICS  Wood grain and texture:  The texture refers to the fineness of the wood structure.  The wood grain refers to the growth rings.  Close-grained or coarse grained refers to the width of the growth rings.  Straight-grained and cross grained refer to the direction of the fibers (parallel or at an Example of Wood Grain Wood Magazine (2018) angle). TIMBER DEFECTS  Timber defects can be in the form of:  Split  Knotholes  Wane  Cup  Crook  Checks  Shake  Bow  Twist Timber Defects https://www.quora.com/What-are-timber-defects-like-shake-checking-wane-and-split  Natural defects: shakes and knots.  MOISTURE CONTENT  Moisture Content:  Water is found in the cell cavities and walls of wood.  Expressed as a percentage using the weight of the piece of wood prior oven-drying and after oven drying.  Freshly sawn wood from living trees have moisture content greater than 100%  Saturated cell walls are termed fiber saturation point.  The fiber saturation point is generally associated with a moisture content of 30%.  Equilibrium moisture content is reached based on surrounding humidity and temperature.  Temperature kilns are used to dry the wood to a specified moisture content.  Oven-dry is used to dry the wood until no further moisture can be driven from the wood.  The process of drying out water from timber is known as “seasoning”/ “seasoned timber.”  MOISTURE CONTENT  Moisture Content:  Rate at which the wood reaches the equilibrium moisture content depends on:  The degree to which the wood has been enclosed or sealed.  The environmental conditions  The wood species.  TYPES OF LUMBER  Types of lumber:  Plywood  Chipboard  Structural glued laminated timber (Glulam)  PLYWOOD  Plywood:  Both softwoods and hardwoods are used.  It is made by bonding together veneers peeled from logs.  The grain of each veneers are set at right angles to the other side, which provides strength in both directions and minimizes thermal movement.  Plywood is an excellent insulator.  Plywood undergoes charring and hollowing when exposed to extreme heat (temperature range from 90 to 150 degrees Celsius).  Depending on the type of adhesive used, they are resistant to moisture Alignment of Grains https://www.britannica.com/science/wood-plant-tissue/Plywood-and-laminated-wood) to humidity (does not warp and crack).  Stronger than traditional timber, flexible, and stress resistant, impact resistant.  CHIPBOARD  Chipboard:  Made from mixing wood particles (wood waste) with an additive to form a sheet material.  Developed primarily for use in furniture.  Wood fibers are shorter making it susceptible to warping and splitting.  Less likely to withstand impact damage than plywood.  More prone to creep under prolonged loading compared to plywood and other timber materials.  Board fibers absorb moisture easily and will crumble and rot if not dried quickly. Chipboard https://www.archdaily.com/catalog/us/products/29602/chipboard-hydrolis-uncoloured- unilin)  It is low cost.  Used mainly to build low-cost indoor furniture.  GLULAM  Glued Laminated Timber (Glulam):  Glued laminated timbers are produced by adhesively bonding dry lumber (1 inches or 2 inches in thickness) under controlled conditions and temperature.  The grains of glulam are parallel.  Glulam can be manufactured in any size and can have curved shapes for architectural purposes.  Glulam can be produced from softwood and hardwood.  Glulam performs well in tension and compression but defects can reduce structural strength.  MANUFACTURING PROCESS OF GLULAM ❖Manufacturing process of Glulam: Example of Glulam https://www.archdaily.com/928387/what-is-glued-laminated-wood-glulam) Glulam Process Watts, A (2016) Example of Glulam Process (VIDEO) https://techlam.nz/about/how-techlam-glulam-is- manufactured/)  BENEFITS OF USING GLULAM  The benefits of structural glued laminated timber are:  They are environmentally friendly.  They are aesthetically pleasing to look at.  They are strong, stuff and durable.  They are stable.  They are fire resistant.  They are cost effective.  They are versatile.  APPLICATIONS GLULAM  Glulam is used as an alternative to steel or concrete for constructing commercial and residential buildings.  It is commonly used for beams and columns. Example of Glulam Application  It can also be used for roofs, domes and https://www.canadianwood.in/applications/structural/ bridges. LUMBER  LEARNING OUTCOMES  List and explain the mechanical properties of lumber  List and explain the preservatives used to treat lumber  List and explain the method of application of the preservatives  INTRODUCTION  Wood is considered a orthotropic material (properties depend on direction of grain).  Strength differs in the longitudinal, tangential and radial directions.  Strength properties parallel to the grain are 20-30 times higher than the properties perpendicular to the grain. Kotlarewski, N. Ozarska, B. and Gusamo, B. (2014)  MECHANICAL PROPERTIES OF LUMBER  Strength:  The ability to bear loads.  Strength of lumber is different due to the grain structure. Compression perpendicular to the grain  Compressive strength, tensile strength and transverse strength.  Compressive strength – the ability to withstand loads. Example, column, posts, Compression parallel to the grain  MECHANICAL PROPERTIES OF LUMBER  Strength:  Compression perpendicular to the grain: the application of a load to a beam/column at right- angle to the grain direction. Compression perpendicular to the grain  Compression strength parallel to the grain: application of a load to the ends of a column. Compression parallel to the grain  MECHANICAL PROPERTIES OF LUMBER  Strength:  Tensile strength – maximum strength of the material before breaking when stretched or pulled (grain structure dependent).  Shear strength: measure of wood to slipping of one part along the grain. Force is applied parallel to the grain.  Parallel or perpendicular to the grain.  Transverse strength – strength of the material before it yields in a flexural test. Example, beams.  Static bending: the application of a load that causes deflection of a beam.  MECHANICAL PROPERTIES OF LUMBER  Hardness:  A measure of the resistance of wood to wear.  Testing method: Janka hardness test. https://en.wikipedia.org/wiki/Janka_hardness_test #/media/File:Janka_hardness_test.jpg  PRESERVATION OF LUMBER  Preservation of lumber is carried out to increase the lumber life and durability.  Types of preservatives of lumber:  Oil type  Organic solvent type  Water-soluble type  PRESERVATION OF LUMBER  Oil type:  Coal tar creosote oil which is a fraction of coal tar distillate.  Suitable for lumber used outdoors.  It can be used alone or with admixtures such as coal tar petroleum oil.  High in toxicity which offers protection against termites. https://takeayard.com/creosote-damp-wood/  Not easy to handle due to odour and difficult to paint the structure.  PRESERVATION OF LUMBER  Organic solvent type:  Organic or inorganic salts dissolved in suitable organic solvents.  Choice of solvents varies based on solubility of preservatives.  Preservatives are often highly flammable.  Examples: copper and zinc naphthenates, trichlorophenol, Chlorpyrifos, etc. https://www.homedepot.com/p/Copper-Green-1- gal-Wood-Preservative- Copper1/100203025#overlay  PRESERVATION OF LUMBER  Water-soluble type:  Applications include outdoor deck, fences, play ground equipment, etc.  Two types:  Leachable Type: inorganic and organic salts that are soluble in water. Preservatives are subject to leaching. Odourless and minor flammability compared to other alternatives.  Fixed Type: mixtures of water soluble salts with fixative salt (sodium or potassium dichromate).  PRESERVATION OF LUMBER  Other method:  Charring  Burning the lumber surface.  Traditional method.  Burnt surface protects the limber from fungi etc.  Wood fencing or telephone poles. https://www.youtube.com/watch?v=nvt2BA091X A  METHODS OF APPLICATION OF PRESERVATIVES  Some methods of application include:  Brushing  Spraying  Injecting under pressure  Dipping and wetting.  METHODS OF APPLICATION OF PRESERVATIVES  Brushing:  This is the simplest method.  Used for applying oil preservatives to well-seasoned lumber (mainly).  Multiple coats is usually applied.  Spraying:  More effective than brushing.  Used for applying water-based solutions or organic solutions.  Solutions are sprayed onto the surface by using a spraying gun.  Time is often saved when using this method.  METHODS OF APPLICATION OF PRESERVATIVES  Injecting under pressure:  Injecting the preservative in lumber under high pressure conditions.  Creosote oil is usually applied in this manner.  Costly process and can only be applied at a special treatment plant.  Dipping and stepping:  Lumber is dipped into the preservative solution.  More effective than brushing and spraying.  Wetting of lumber is performed for days or weeks.  THANK YOU ANY QUESTIONS?