KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Content • Wood properties in the building • Durability Timber and its properties Wood properties in the building Durability, fire and other aspects of environmental performance – Natural durability – Treatment potential • Fire performance • Environmental performance – Insulation & specific heat capacity – Acoustic transmission Insect trail on a log under the bark www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics Properties critical to building use Strength and stiffness Colour Visual consistency Flat & stable Wood properties in the building Hardness & toughness Durable outside Durable inside Fire resistance Limited spread of flame Limited developed smoke Thermal insulation Acoustic moderation www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics Wood s characteristics and properties Wood’s properties Durability Fire Performance Env Performance Durability – in ground Char rate Conductivity (U) – Insulation (R) Durability - above ground Spread-of-flame Specific heat capacity Termite resistance Smoke developed Acoustic transmission Lyctid resistance Chemical resistance Preservative retention Electrical Conductivity These are all broadly species related Timber and its properties www.csaw.utas.edu.au Timber and durability Natural durability and timber’s breakdown Wood s treatment potential www.csaw.utas.edu.au 1! KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics The nature of timber Weathering • Timber is a natural but biodegradable product • It is affected: • The greying and minor cracking of timber due to the mechanical or chemical breakdown of the wood surface by: – Weathering – Decay – Attack by insects and similar organisms – exposure to light, breaking down wood molecules – action of dust and sand, and – alternate shrinking and swelling due variation in moisture content • The impact of these breakdown mechanisms vary with the: • The effects are often limited to the surface – Nature of the wood – Exposure to hazard A weathered fence post Timber and its properties www.csaw.utas.edu.au Timber and its properties KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Weathering Weathering • The rate depends on the exposure level www.csaw.utas.edu.au • Weathering can be: – more severe on end grain – severe on some surfaces as wood can delaminate – It is usually very slow – ~ 0.1 mm per year depending on species and board orientation • Preservative treatment does not affect the weathering rate • It affects: – appearance, – the performance of finishes; and – eventually, decay rate A weathered bridge deck element Weathering of untreated and unfinished elements Timber and its properties www.csaw.utas.edu.au Timber and its properties KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Decay Decay • Decay rates vary with: • Decay is the decomposition of wood by fungi • Fungi occur in a variety of forms, ranging from large fruiting bodies to microscopic moulds • To establish and sustain itself, the fungi need air, moisture and food • Decay can occurs if the wood – – – – – The wood’s character – Its moisture content – The ambient temperature • It occurs most readily in timber kept regularly moist, – Particularly in ground contact • It can occur on any surface of a piece – Decay tends to attack the moisture-permeable end-grain most vigorously is available as food has access to oxygen is above 20% MC temperature is between about 5° to 60°C Timber and its properties www.csaw.utas.edu.au • Decay hazard is often assessed above ground and in-ground contact www.csaw.utas.edu.au Timber and its properties www.csaw.utas.edu.au 2! KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Moisture impacts In-ground decay zones Bridge logs after ~ the same service life: One exposed to the weather, the other protected by a water-proof deck FWPA 2010 Timber service life design guide Timber and its properties www.csaw.utas.edu.au Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Above ground decay zones Insects and other organisms • Insects and similar organisms can consume timber • These include: – Subterranean termites; – Lyctid beetles; and – various marine organisms FWPA 2010 Timber service life design guide Timber and its properties www.csaw.utas.edu.au Timber and its properties KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Termites Termite hazard zones www.csaw.utas.edu.au Termite nest in a log • Termites are cellulose-eating insects that occur in all parts of Australia – They are rare in Tasmania and parts of Victoria • Some species build and live in nests in the ground, in logs and in cavities in buildings and other locations, traveling to edible cellulose in moist earth galleries Timber and its properties www.csaw.utas.edu.au FWPA 2010 Timber service life design guide Timber and its properties www.csaw.utas.edu.au 3! KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Lyctid beetles Lyctid beetles • Lyctid moths lays their eggs in the vessels in the sapwood of susceptible hardwoods • Once hatched, the larvae eats the starch-rich sapwood • On maturity, the beetle leaves via an exit hole • Lyctid susceptible sapwood can be attacked at any time, even after years in service • Most standards limits its inclusion in timber elements Timber and its properties www.csaw.utas.edu.au Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Marine organisms Hazard classes Exposure hazards are categorized into classes Hazard Class Exposure Timber and its properties www.csaw.utas.edu.au Service Conditions Biological Hazard H1 Inside above ground Fully Protected, Well ventilated Borers Only H2 Inside above ground Protected from Wetting, Nil leaching Borers and termites H3 Outside above Moderate wetting and ground leaching Decay borers& termites H4 Outside in ground Severe wetting & leaching Severe decay, borers & termites H5 Ground contact Extreme wetting, leaching &/or critical use Very severe decay, borers and termites H6 Marine waters Prolonged immersion in Nth & Sth sea water Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Resistance to hazards Life expectancy • Timber resists hazards through its natural durability and any applied treatment • Natural durability varies with species through: Class Probable in-ground life Probable above-ground expectancy (years) life expectancy (years) – The profile of extractives stored in wood Some extractives are toxic to fungi and insects – The cell structures Some species allow certain insects to breed in the cells Others not • To simplify design, natural durability is rated in durability classes Species Greater than 25 Greater than 40 Ironbark, Tallowwood 15 to 25 15 to 40 Spotted gum, Blackbutt, WRC to 15 to 15 Brush box, Southern blue gum, Messmate to to Vic ash, Radiata pine, Douglas fir The ratings in this table are based on expert opinions and the performance of the following test specimens: (a) In-ground: 50 × 50 mm test specimens at four sites around Australia (b) Above-ground: 35 × 35 mm test specimens at eleven sites around Australia – in-ground contact and – above-ground • With few extractives and a high starch content, all sapwood is rated as Class Timber and its properties Marine wood borers and decay www.csaw.utas.edu.au Timber and its properties www.csaw.utas.edu.au 4! KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Life expectancy – Marine Treatment Class Probable marine-borer-resistance life expectancy in southern waters (years) Greater than 60 41 to 60 21 to 40 to 20, usually less than * NOTE: Marine borer resistance is based on natural round piles containing 350 mm diameter of heartwood in southern seas reaching from Perth in the west to Batemans Bay in the east Only class timbers can be expected to give reasonable service life (12 to 30 years) in northern waters Timber and its properties www.csaw.utas.edu.au • Timber s natural durability can be improved by introducing treatment chemicals into the wood • These protect it from fungi, insects and other biological agents • The level of protection is governed by the toxicity and amount of chemicals retained in the wood • The target retention of chemicals is set for the intended Hazard Level • As the chemicals are carried in a liquid, wood s permeability limits the effectiveness of treatments – It is very hard to reliably achieve the target chemical retentions in heartwood Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Major wood preservative treatments Treatment really only benefits sapwood • Insecticides and fungicides are applied by coating, dip diffusion or commercial pressure treatment: – for appearance timber to H2: • Water-borne mixtures applied to unseasoned timber • Light organic solvent-borne preservatives (LOSP) applied to seasoned and finished product – for structural timber to H5 – H6 • Water borne mixtures like CCA, Tanalith E and ACQ applied to material for external applications • LOSP surface insecticide treatment H2-S treated LVL Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics The wood s permeability really does limits the treatment s effectiveness Heartwood is very hard to treat reliably, especially in hardwood This is due to its cell structure Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics Fire requirements • To ensure occupant safety during a fire, the BCA establishes requirements addressing the: Durability - Fire performance – Fire resistance of the structure – Spread of fire between compartments – Fire performance of egress paths – Performance during bushfires • This imposes requirements on a material s performance in a fire for: – – – – – www.csaw.utas.edu.au Structural behavior in fire Loss of integrity Spread of flame across its surface The amount of smoke developed Propensity to flash into flame at key temperatures Timber and its properties Myer’s fire, Hobart www.csaw.utas.edu.au 5! KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Wood s fire performance Sacrificial charring rate • Wood burns in a fire • As it does, it develops an insulating carbon layer over its surface • This charring layer reduces the rate of loss of effective section • Element can be design with a sacrificial layer that burns while the section retain structural adequacy for the required time • Reduced cross section must carry the design “fire load” Timber and its properties Rate of charring to AS 1720.4 is C = 0.4 + (280/D)2 where C = notional charring rate in mm/min D = timber density at 12MC in kg/m3 www.csaw.utas.edu.au Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Sacrificial charring material Other specific performance requirements • Floor coverings – Critical radiant flux and – Smoke development rate • Walls and ceiling – Fire hazard properties (propensity to flash into flame) • reported in Material Groups Timber is rated Group (of 4) – Average extinction areas Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics Thermal properties of common material Material Environmental Performance: Insulation & specific heat capacity U-Value (W/mK) R-Value (100 mm) Rock wool insulation 0.045 2.22 0.75 ~ 30 Softwood 0.12 0.83 2.0-2.9 ~450 Hardwood 0.16 0.63 2.0-2.9 ~850 Glass 3-5 0.007 (3mm) 0.84 ~3,000 Concrete www.csaw.utas.edu.au Specific heat Density capacity (kj/kgK) (kg/m3) 0.9 - 0.05 0.8-0.9 ~2,400 Steel 46 0.0022 0.5 ~7,850 Aluminium 250 0.0004 0.9 ~2,700 Timber and its properties www.csaw.utas.edu.au 6! KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Definitions • U-value thermal conductivity is the rate that heat will conduct through a material • R-value Insulation value = 1/U-value * thickness (in metres) • Specific heat (or thermal) capacity is the amount of heat energy held in a material at a given temperature Timber and its properties Environmental Performance: Acoustic transmission www.csaw.utas.edu.au www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Sound Timber and acoustic performance • Vibrating object produce a series of compressions and rarefactions in the air surrounding it • These fluctuations in air pressure travel away at relatively high speed • They gradually die off as their energy is spread over a wider area and absorbed by the medium • Sound is the sensation produced by the ear when stimulated by these vibrations • Timber tends to absorb sound energy and dampen acoustical vibrations • Its cells structure converts sound energy into heat energy by: – frictional and viscous resistance within these cells – vibrations within their substructure • This damping reduces the tendency of structures to transmit vibrations long distances • It also reduces the magnitude of resonant vibrations, improving the performance of wood panelling as a reflective surface Thanks to Square1: www.sq1.com Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics Timber and chemicals resistance • Timber offers considerable resistance to chemical attack including Environmental Performance: Chemical resistance – organic materials, – hot or cold solutions of acids or neutral salts and – dilute organic and mineral acids • Due to this, it is commonly used for chemical storage vats and tanks and for structural members in corrosive environments www.csaw.utas.edu.au Timber and its properties www.csaw.utas.edu.au 7! KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Timber and chemicals resistance Summary • Building applications demand a critical range of properties from wood • Timber is subject to a range of biological hazards It resists these through its natural or treated durability • Timber burns in fire but does so at a known rate This allows confident fire design • Timber is a reasonably efficient insulator with useful specific heat capacity • It also has useful acoustic and chemical resistance properties • Direct contact with caustic soda should be avoided Strong acids and alkalies will destroy timber in time, with alkaline chemicals more likely to cause cellular degradation than acidic ones • In general, heartwood is more resistant to chemical attack than sapwood, due to its limited permeability • Softwoods resistance chemical attack more successfully than hardwoods due to their lower hemicellulose and higher lignin content Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics Thanks to Patrick Cook Timber and its properties www.csaw.utas.edu.au Timber and its properties www.csaw.utas.edu.au 8! ... its properties www.csaw.utas.edu.au FWPA 2010 Timber service life design guide Timber and its properties www.csaw.utas.edu.au 3! KDA5 03/ 335 Timber, its origin and characteristics KDA5 03/ 335 Timber,... and unfinished elements Timber and its properties www.csaw.utas.edu.au Timber and its properties KDA5 03/ 335 Timber, its origin and characteristics KDA5 03/ 335 Timber, its origin and characteristics... design guide Timber and its properties www.csaw.utas.edu.au Timber and its properties www.csaw.utas.edu.au KDA5 03/ 335 Timber, its origin and characteristics KDA5 03/ 335 Timber, its origin and characteristics