KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Content Timber and its properties Overview of all properties Structural, visual and other performance concepts Structural performance indicators with wood System for structural grading 0.0 title ! www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics • Wood’s properties • Concepts in building performance • Wood’s structural properties • Grading standards and processes Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics Woods characteristics and properties Wood’s characteristics Natural Bio-degradable Anisotropic Hygroscopic Renewable Variable across and along the tree and between trees Wood’s (and timber’s) properties Recyclable Wood’s properties Basic Structural Stability Durability Density Stiffness (MOE) Board stability Durability – in ground Specific gravity Strength (MOR) Unit shrinkage Durability - above Impact resistance Strength group Grain pattern Hardness Joint Group Lyctid resistance Toughness Creep Preservative retention ground www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics Timber and its properties Termite resistance www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics Woods characteristics and properties Wood’s properties Fire Performance Env Performance Visual Character Char rate Conductivity (U) – Insulation (R) Colour Feature Spread-of-flame Specific heat capacity Colour Clear wood Smoke developed Acoustic transmission Colour consistency Gum vein - kino Chemical resistance Grain Knots Electrical Conductivity Texture Insect feature Figure Timber and its properties www.csaw.utas.edu.au Concepts in building performance Required: Structural adequacy and other aspects of safety Desirable: Appearance, durability and other aspects of the built environmental www.csaw.utas.edu.au 1! KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Required building performance Performance requirements - structural performance level dictated by regulation • In Australia, basic building performance is regulated by the National Construction Code (NCC) • This establishes the minimum required performance for: A building or structure, to the degree necessary, must— i. remain stable and not collapse; ii. prevent progressive collapse; iii. minimise local damage and loss of amenity through excessive deformation, vibration or degradation; iv. avoid causing damage to other properties by resisting the actions to which it may reasonably be subjected – Health – Safety, • including structural adequacy and safety from fire – Amenity and – Sustainability 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 Performance requirements - structural The NCC then calls up a suite of standards used to determine structural integrity and design processes, including AS 1720.1 Design of timber structures Timber and its properties Basic structural concepts www.csaw.utas.edu.au www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Results of force Results of force • Compression: pushing together • Moment: The rotational effect of a force times distance • Tension: pulling apart • Shear: Unaligned forces acting in opposition Tends to tear through Timber and its properties • Torsion: Rotational effect of eccentric force 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 Result of force Loads • Stress: internal forces per unit area It can be compressive or tensile • Live: people, cars, wind • Dead: Weight of the structure • Strain: elongation or compression caused by the stress; 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 Aspects of an element Aspects of a material in design • Strength: the ability of a member to resist a load without failure • Strength (when it breaks) • Serviceability: design for a quality of action, not just resistance to failure • Stiffness (how much it bends) – Modulus of Rupture (MOR) – Modulus of Elasticity: a material’s characteristic relationship of stress to strain (MOE) Stress / strain relationship of common materials 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 Primary structural properties for timber Allowance for material variability • The tested performance of many materials varies around some mean value • Design values are generally taken at the point at the lower 5th percentile – 95% of the test population has a higher performance MOE and MOR of the timber plus specific characteristics, including: 1. Compression strength parallel to grain; 2. Compression strength perpendicular to grain; 3. Tension strength parallel to grain; 4. Tension perpendicular to grain; and 5. Shear strength parallel to grain Timber and its properties www.csaw.utas.edu.au UBC 2009 Wood474 Li Wood Strength & Mechanics Timber and its properties www.csaw.utas.edu.au 3! KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Desired building performance • Appearance – The combined effects of colour, texture, grain and feature • Durability Wood’s structural properties – Resistance to biodegradation at various hazard levels • Thermal performance – Insulation and specific heat capacity Grain structure and structural performance Features and their influence on strength Performance over time: creep • Acoustic performance • Chemical and other resistance Next two weeks Timber and its properties www.csaw.utas.edu.au www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Cell structure and directionality Cell structure, strength & stiffness rad longitudinal tan ge nti al Timbers strength is related to: • Properties of the cell structure • Cell size and direction ial Vessels and fibers in birch Source: http://www.swst.org/teach/set2/struct1.html • Wood is anisotropic Its properties vary radially, tangentially, and longitudinally • The cell structure is primarily longitudinally arranged tubes Timber and its properties www.csaw.utas.edu.au Strong parallel to grain & stiff parallel to grain Weak perpendicular to grain Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Relative strength Primary structural properties for timber Tension & compression along the grain: 10 units Tension & compression across the grain >1 units Timber and its properties www.csaw.utas.edu.au MOE and MOR of the timber plus specific characteristics, including: 1. Compression strength parallel to grain; 2. Compression strength perpendicular to grain; 3. Tension strength parallel to grain; 4. Tension perpendicular to grain; and 5. Shear strength parallel to grain Timber and its properties www.csaw.utas.edu.au 4! KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Key structural properties Strength-reducing characteristic • Strength (when it breaks) and stiffness (how much it bends) values are influenced by: – moisture content, – grain structure of the species, – slope of grain in the piece, – other features in the piece Timber and its properties • Knots: part of a branch; • Grain direction: sloping or irregular; • Check and shakes: small surface cracks or splits; • • • • www.csaw.utas.edu.au Bark and heart or pith Gum vein, resin pockets Insect attack; and Others Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Creep deformation Duration of load effects Wind loads Instantaneous loads 1.5 k1 Strength 0.5 Duration of load • Creep is time-dependant increase in deformation Under constant load, cells permanently change shape and deformation increases • Some deformation remains once load removed Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics sec hrs day mth 50 yr • Irreversible and cumulative strength loss related to the duration of peak load over the lifetime of the structure – Different load combinations have different duration of load effects Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics Determination of structural capacity Species Grading standards and processes sorting a natural variable material into groups with reliable strength Theoretical ‘clear wood’ properties and determination of strength groups In-grade testing Variation coefficient for structural grade Stresses grades and allowable stress Joint group www.csaw.utas.edu.au Determine characteristic species strength Testing short clears The piece Structural grade (visual) The portion of strength in the piece compared to an ideal clear piece Structural capacity Stress grades Defined sets of structural properties Species strength group Cluster of species with similar strength characteristics Piece assessment - Visual using structural grade - Machine using grade parameter Grade parameter Piece stress grade (F17, MGP 12, etc) structural properties In-grade testing to determine relationship of parameter Timber and its properties www.csaw.utas.edu.au 5! KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Evaluation of species properties Population characteristics set the level • Small clear samples – Testing of determine characteristic species properties reflecting wood fibre strength – These value are modified significantly to allow for strength reducing natural features • In-grade testing – Batch testing of commercial sized timber under realistic loading conditions to determine actual characteristic of a population – Correlation of parameters for MOE and MOR 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 Strength groups - species related Structural groups - piece related Based on species testing work since the 1930’s, species are assigned strength groups Unseasoned timber Seasoned timber Example species S1 SD1 Grey coast box S2 SD2 Blackbutt S3 SD3 Messmate S4 SD4 Alpine ash, Mountain ash S5 SD5 Douglas fir, slash pine S6 SD6 Radiata pine SD7 Mahogany SD8 Western red cedar Timber and its properties www.csaw.utas.edu.au www.csaw.utas.edu.au • Process for visual sorting timber sticks into groups with differing strength-reducing characteristics Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Stress grades – related to groups of sticks Strength group/stress grade/structural grade • Stress grades define an assigned set of structural properties for use in design TABLE 2.4 STRUCTURAL DESIGN PROPERTIES FOR F-GRADES Stress Grade F34 F27 F14 F11 F8 F7 F5 F4 Bending (f 'b) 100 80 40 35 25 20 16 13 Timber and its properties Characteristic strength, MPa Tension parallel to Shear in grain beam (f 't) Hardwood Softwood (f 's) 60 50 7.2 50 40 6.1 25 21 3.7 20 17 3.1 15 13 2.5 12 10 2.1 9.7 8.2 1.8 7.7 6.5 1.5 Compression parallel to grain (f 'c) 75 60 30 25 20 15 12 9.7 Characteristic short duration average modulus of elasticity parallel to grain, Mpa (E) 21 500 18 500 12 000 10 500 100 900 900 100 www.csaw.utas.edu.au Timber and its properties www.csaw.utas.edu.au 6! KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Stress Grades Grading is a vital link • Limited number of grade descriptions – F grade system - hardwood and softwood – MGP grades - machine graded woods • Both pine and hardwoods (after all the testing) – GL grades - glued laminated timber – A grades - currently Victorian Ash Producer • • • Designers and Builders • • Grading is the link between the producer, designer & user Timber and its properties sorts timber into groups with similar properties grades timber - product with similar properties assigned a grade (structural, or appearance) stamps structural timber to indicate stress grade, species, moisture content, treatment, type of grading www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics rely on producers to grade timber products accurately and consistently specify and use timber by grade to ensure the product used for a specific purpose has appropriate properties to satisfy functional requirements Timber and its properties www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics Summary • Each species and piece of timber has specific properties – These can be grouped around particular performance requirement areas • Performance requirements in building can be required (regulated) or desirable • Structural performance is a critical requirement in building It is heavily regulated • Timbers anisotropic and hygroscopic nature influence its structural performance and the means by which it is graded • Several grading methods are used to sort the material into groups with similar structural properties • Grading provides a vital link between the producer and the designer Timber and its properties www.csaw.utas.edu.au Timber and its properties www.csaw.utas.edu.au 7! ... Hardwood Softwood (f 's) 60 50 7.2 50 40 6 .1 25 21 3.7 20 17 3 .1 15 13 2.5 12 10 2 .1 9.7 8.2 1. 8 7.7 6.5 1. 5 Compression parallel to grain (f 'c) 75 60 30 25 20 15 12 9.7 Characteristic short duration... structural properties for use in design TABLE 2.4 STRUCTURAL DESIGN PROPERTIES FOR F-GRADES Stress Grade F34 F27 F14 F 11 F8 F7 F5 F4 Bending (f 'b) 10 0 80 40 35 25 20 16 13 Timber and its properties. .. grain, Mpa (E) 21 500 18 500 12 000 10 500 10 0 900 900 10 0 www.csaw.utas.edu.au Timber and its properties www.csaw.utas.edu.au 6! KDA503/335 Timber, its origin and characteristics KDA503/335 Timber,