CE 1205 CONSTRUCTION MATERIALS WEEK 13 Chapter 8

CE 1205 CONSTRUCTION MATERIALS WEEK 13 Chapter 8 TIMBER Power. Point® Slides by Salmaliza Salleh Last Updated: © LMS SEGi education group 1

Chapter Overview • Chapter 8 exposed you the properties of timber. • You also learned the types of timber natural defects. Last Updated: © LMS SEGi education group 2

Learning Objectives • Last Updated: To expose the students properties of timber and types of natural defects. © LMS SEGi education group 3

Learning Outcomes • Last Updated: At the end of the class, students must be able to define the properties of timber and types of natural defects. © LMS SEGi education group 4

INTRODUCTION Wood is very versatile raw material & is still widely used in construction in countries like Canada, Sweeden, Finland, Norway & Poland. Last Updated: © LMS SEGi education group 5

1. 0 Structure of Wood • Cross section of a tree a. b. c. d. Last Updated: Heartwood Pith Bark Sapwood © LMS SEGi education group 6

Looking at the cross section of a tree, the trunk consists of a series of concentric rings covered by a layer of bark. ____ • • _________ • • Trunk consists of rings which represents one year of tree growth _______ • • The inner layer and older wood, darker, drier, and harder than the living layer. _______ • • Last Updated: The tree’s outer layer The living layer which has lower natural decay resistance. © LMS SEGi education group 7

Function of the trunk is: • • Last Updated: To convey a solution called _______ to the leaves, & To support the ______ at such height as to ensure a sufficiency of air & light. © LMS SEGi education group 8

2. 0 Species of Timber In Malaysia, there are more than 2500 species of timber. Table 1. 0 shows the lists of Malaysian timber which are grouped botanically into hardwoods and softwoods. Last Updated: © LMS SEGi education group 9

Hardwoods • Sometimes referred to as pored wood because of the presence of large cell called ‘vessels’ which perform the function of conduction. • Grouped based on the density and durability; heavy hardwoods, medium hardwoods & light hardwoods. • Application: furniture, cabinets, paneling, interior trim & specialty items. Last Updated: © LMS SEGi education group 10

Softwoods • Are referred to as ‘non-pored’ wood and the cells provide conduction and mechanical support occur principally in the spring wood. • Softwoods are used for general construction and structural purposes Last Updated: © LMS SEGi education group 11

Timber Categories • Softwoods • • Last Updated: • Derived from trees with needle-shaped leaves & usually evergreen E. g. fir, larch, pine, spruce, hemlock Hardwoods • • © LMS SEGi education group Derived from trees with broad leaves & are usually deciduous E. g. ash, elm, oak, teak 12

3. 0 Strength Classes The strength class system is defined primarily by bending strength. For Malaysian timber, the strength class will be based on its moisture content. Based on strength, FRIM divided the timber into four groups; A, B, C, and D. (Table 2. 0) For structural purposes, FRIM divided stress of timber into three grades: • • Last Updated: selected grade standard grade common grade (Table 3. 0) © LMS SEGi education group 13

4. 0 Factors Affecting Strength of Timber • • Last Updated: Density Moisture content Temperature Grain structure • • • Position in tree Condition of growth Defects (Table 4. 0) © LMS SEGi education group 14

4. 1 Density • • • Last Updated: The higher the density, the higher the mechanical properties. ______ trees often give timber of very low density. The weight of timber is reduced by ______ and most strength properties increased. © LMS SEGi education group 15

4. 2 Moisture Content • Last Updated: Can be determined either by the oven-dry method or electric-moisture-meter method. © LMS SEGi education group 16

4. 3 Temperature • With ______ temperature, the strength of timber _____ • A permanent loss of strength may result if wood is held at high temperature for a long period. Last Updated: © LMS SEGi education group 17

4. 4 Grain Structure • Last Updated: Determines the permissible stress and modulus of elasticity. (Table 3. 0) © LMS SEGi education group 18

4. 5 Position in Tree • In soft wood, the wood near the _____ of tree is denser, stronger and harder. • The wood often tends to become stronger with increasing distance from ______ Last Updated: © LMS SEGi education group 19

4. 6 Condition of Growth • Environmental factors e. g. • • Last Updated: Height above sea-level, temperature, rainfall, spacing between trees, etc. © LMS SEGi education group 20

4. 7 Defects Classified into: • _____; branch section cut with board _________; caused by fungi _______, and Marine Organism i. iii. • • Shake, Split and Checks iv. • • • Last Updated: Termites larvae, beetles Marine organism attacks timber in contact with water Shakes occur between annual rings Splits caused by handling Checks occur across the annual ring © LMS SEGi education group 21

5. 0 Timber as Structural Material Structural usage of timber can be classified as: • • • Last Updated: Marine structure – e. g. wharves, cofferdams, etc. Heavy construction works – e. g. timber piles, bridges, etc. Medium/ Light Construction works – e. g. roof trusses, room’s partitions, floors, formwork, etc. © LMS SEGi education group 22

EXAMPLES Timber Bridge Last Updated: Timber Piles & Piers Cofferdam Formwork © LMS SEGi education group 23

Principal characteristics of timber can be divided into: Density ______ : proportional to the amount of water removed. Warping: flat surface become distorted e. g. bow, crook, twist. _______: Natural resistance to fungal decay and termites (also known as white ants). • • • Last Updated: Decay: is a breakdown of wood by the action of wood destroying fungi when the condition of moisture, air supply and temperature are suitable. Strength © LMS SEGi education group 24

6. 0 Wood Based Panel Product • • Last Updated: Wood based panel products are sheet materials which contain a significant amount of wood in the form of ____, veneers, chips, flakes, or fibres. E. g. : plywood, glue laminated timber, particle board, & fibre building board. © LMS SEGi education group 25

7. 0 Preservation of Timbers should be suitably treated. The choice of preservative treatment depends upon: • • • Last Updated: type of wood the initial cost of the timber & treatment the usage cost of maintenance © LMS SEGi education group 26

Type of preservative commonly used: 1. 2. 3. 4. 5. Last Updated: Coal Tar Creosote Tar oil Petroleum oil Water-borne Preservatives Boric Acid or Borax © LMS SEGi education group 27

1. _______ Creosote • • • Last Updated: Produced by the distillation of bituminous coal (creosote oil). Highly toxic to ______, insects and marine worms. If ______ and _______ introduced into wood, good protection from termites, decay and marine organism. © LMS SEGi education group 28

2. Tar ______ • • Last Updated: Distilled from wood tar or coal tar. Do not leach in water or corrode the metal. High viscosity and often used for surface treatment. Considered as _______ preservative. © LMS SEGi education group 29

3. _____ Oil • • • Last Updated: Crude, refined or residual (fuel) petroleum oil. Not very effective Insufficient toxicity towards fungi to prevent decay. Expensive, highly inflammable and strong smell. Suitable for ______ or cold _____ © LMS SEGi education group 30

4. Water-borne Preservatives • • Last Updated: Inorganic – _______, ____ and _____ salts. Ease of handling with clean, paintable surfaces. _____, non-flammable, cheaper. Resistance to fungi and insects but little protection against weathering. © LMS SEGi education group 31

5. Boric Acid or ______ • • • Last Updated: Give immunity to veneer and sawn timber against weathering. Clean, permanent, and free from health danger. Do not stain or colour the wood. © LMS SEGi education group 32

Method of treating timber: Pressure process • • • Non-pressure process • • • Last Updated: Pressure greater than the atmospheric are employed The actual pressure depends on the species, preservative and treatment. Hot and cold bath treatment Steeping/_____ in water-soluble preservative ____ Swabbing _____ © LMS SEGi education group 33

ANY QUESTIONS? Picture retrieved from http: //www. free-pressrelease. com/members_pic/200807/img/1217532713. jpg Last Updated: © LMS SEGi education group 34

References • John, V. B. (1992) Introduction to Engineering Materials, 3 rd edition, Mc. Millan Press Ltd. • Everett, A. (1996). Materials, 3 rd edition Addison Wesley Longman Limited, England Last Updated: © LMS SEGi education group 35