Building materials by Sourav Zaman, Lecturer Department of Architecture Northern University of Business and Technology

1. COURSE NO: ARCH 1201
COURSE TITLE: BUILDING MATERIALS
Lecture 3
TIMBER

3. MECHANICAL PROPERTIES OF TIMBER:
Durability
Depends on-
Natural and artificial defects
Thickness, length and straightness
Regular annual ring
Uniform and dense
Well seasoned
“Any wood used in engineering construction is
termed as timber.”
Strength
1. Tensile strength
2. Compressive strength
 Main stress
 Depends on anatomical structure
and moisture content
3. Flexural strength
 Found in timber beams
A Text Book of Engineering Materials- by Dr. M. A. Aziz

4. •Easy to work
•Comparatively stronger than other common materials compared in
proportion to weight
•Both load bearing and non-load bearing
•Very economic and low wastage
•Low thermal conductivity
•High electrical resistance
•Good sound proofing property
•Unquestionably durable when properly treated
•Contemporary timber products can add lightness and beauty
•Great resale value
ADVANTAGES (Using Timber as a building material)
A Text Book of Engineering Materials- by Dr. M. A. Aziz

5. Annual growth rings
Rapid growth in spring and slow in
summer, no wood added during winter
Spring wood and Summer wood
Pith
The center
Sapwood and Heartwood
SOME IMPORTANT TERMS (About Timber/ Timber
processing)
A Text Book of Engineering Materials- by Dr. M. A. Aziz

6. Principal methods of sawing logs are-
1. Ordinary or cross sawing
2. Radial or Rift sawing
3. Quarter sawing
4. Tangential or Slash sawing
SAWING OF TIMBER
A Text Book of Engineering Materials- by Dr. M. A. Aziz
“The conversion of logs into various market forms of timber is generally
done by sawing.”

7. Natural defects
Knots
Twisted fiber
Shakes
•Radial shake
•Through shake
•Ring shake
•Cup shake
Upsets
Foxiness
Rind galls
DEFECTS IN TIMBER
A Text Book of Engineering Materials- by Dr. M. A. Aziz
Knots
Twisted Fiber
Shakes
Foxiness
Rind galls
Upsets

8. Artificial defects
Warping
Splitting and cracking
Fungal infections
Insects and worms
DEFECTS IN TIMBER
A Text Book of Engineering Materials- by Dr. M. A. Aziz

9. SEASONING IN TIMBER
• As fresh timber contains about 30 to 40
% sap or moisture.
• This sap is very harmful for the life of a
timber
• All those methods which are used for
removing the sap from timber are
collectively termed as seasoning of
timber.
A Text Book of Engineering Materials- by Dr. M. A. Aziz
Methods of Seasoning of Timber
1. Natural (air seasoning )
• Long outdoor exposure to air
• Staked on dry elevated platform, covered from
rain
• Turned frequently for equal drying
• Very slow process, takes 2 to 3 years

10. Methods of Seasoning of
Timber
2. Natural (water seasoning )
• Immerged in water and stands for
couple of days
• Then dried in natural air
• Well suited for timber, containing lots
of sap
A Text Book of Engineering Materials- by Dr. M. A. Aziz

11. Methods of Seasoning of
Timber
2. Artificial seasoning
Kiln seasoning
• Temperature 70 to 82 degree Celsius
• Requires 4-6 days or 3-6 months for first
shrinkage. Then exposed to higher
temperature for 6-12 days
• Two types of kiln…Compartment kiln and
Progressive kiln
• Used in Bangladesh
Chemical seasoning
• Also known as “salt seasoning”
• Before placed in the kiln, timber is soaked
into salt bath (generally Urea)
• Uniform and fast drying
A Text Book of Engineering Materials- by Dr. M. A. Aziz
Kiln seasoning

12. Methods of Seasoning of
Timber
2. Artificial seasoning
Electrical seasoning
• High frequency alternative currents are
passed through timber
• Quick process but not used in Bangladesh
Steaming
• Takes 4-6 hours
• Reduces elasticity and strength of timber
Boiling
• Emerged in boiling water for certain period
of time
A Text Book of Engineering Materials- by Dr. M. A. Aziz
Smoke seasoning
• Used in boat making industry

13. • Strong, stiff, tough, durable
• Free from both natural and artificial defects
• Regular, uniform annual growth ring
• Uniform and lustrous color
• When struck with hammer, timber should give a clear sound
• Being obtained from the heart of a full grown tree
• High density
• Good workability
• Should be elastic
• Resistance to compression
• Should be fire resistant, thus dense not light and porous.
• It should retain the shape during the period of use
CHARACTERISTICS of Good Timber
A Text Book of Engineering Materials- by Dr. M. A. Aziz

14. Juri Troy Architects' passive House Under The Oaks in Austria

15. Wooden house in Holland from Onix Architects Wooden house in Austria

16. RECOMENDED REFERENCES
Aziz. M. A: Engineering Materials.
Smith, R. C: Material of construction.
Andres, C. K: Manufactures manuals and brochures,