wood as a building material.... structural information

1. LIST OF MATERIAL USING IN THE STRUCTURE:
1. FABRIC
2. BRICK
3. PAPER
4. GLASS
5. WOOD
6. STONE
7. STEEL
8. ALUMINIUM
9. PLASTIC
10.MUD

2. WOOD
A STRUCTURAL MATERIAL

3. Introduction of Wood:-
1. Wood may have an “image problem” for being
low tech. Remember that the paper mill and board
mills are very sophisticated. The worst property of
wood is that it is common, so we feel comfortable
dangerous approach…
2. The fears of shortage of timber can be
considerable
3. Low energy to produce. The downside is that it
requires more labor intensive during construction.

4. Introduction of Wood:-
4. De Havilland built the Mosquito bomber with wood. It
was extremely successful. During WW II 7,781 bombers were
built. Over 5,000 wooden gliders were built in England for
the invasion of Normandy in1944.
5. Recent bad jobs in condos have damaged the
reputation of wood.
6. Wood is biodegradable, which may be good,
however we are not into disposable houses, so we
need to be careful preserving and protecting.

5. 1. STRUCTURAL PROPERTY OF WOOD.
2. GENERAL PROPERTY OF WOOD.
3. USAGE OF WOOD IN BUILDING AS A STRUCTURAL MEMBER.
4. PRACTICAL STRUCTURAL APPLICATION.

6. STRUCTURAL PROPERTIES OF WOOD
1. STRENGTH
2. DEFORMATION RESISTANCE
3. HARDNESS
4. FATIGUE RESISTANCE(TIME LOSS OF STRENGTH)
5. UNIFORMITY OF PHYSICAL STRUCTURE

7. 1> STRENGTH:
A GOOD WOOD SHOULD BE STRONG FOR WORKING AS A STRUCTURAL MEMBER SUCH
AS JOIST, BEAM, RAFTER ETC. IT SHOULD BE CAPABLE OF TAKING LOAD SLOWLY OR
SUDDENLY. IT SHOULD ALSO POSSESS ENOUGH STRENGTH IN DIRECT AND TRANSVERSE.
The strength of wood is highly dependent upon direction:
Tensile strength values in
Longitudinal : radial : tangential directions on average are in the ratio of 20:1.5:1.
The variation of strength between different directions can be attributed to the fine
structure of the wood cells.

8. MATERIAL E DENSITY TENSILE /
DENSITY
COMPRESSIVE
DENSITY
WOOD 20-30 120-170 60-90
MILD STEEL 26 30 30
ALIMINIUM 25 180 130
CONCRETE 15 3 30
Comparison with other materials:-

9. Nails close to the end splits lumber easily
because of the weak bond between
the fibers.

10. 2> DEFORMATION RESISTANCE:-
THE WOOD SHOULD BE EASILY WORKABLE. IT SHOULD NOT CLOG THE TEETH OF SAW
AND SHOULD BE CAPABLE OF BEING EASILY PLANNED OR MADE SMOOTH.
IT MAY BE MENTIONED THAT THE CHIEF FACTORS AFFECTING THE STRENGTH OF WOOD
ARE AS FOLLOWS:
1. ABNORMALITIES OF GROWTH
2. FAULTS IN SEASONING
3. INVASION OF INSECTS
4. IRREGULARITIES OF GRAIN
5. MOISTURE CONTENTS
6. PRESENCE OF KNOTS, SHAKES ETC.
7. WAY IN WHICH A WOOD PIECE IS CUT FROM THE LOG ETC.

11. 3> HARDNESS:-
1. A GOOD WOOD SHOULD BE HARD I.E. IT SHOULD BE OFFER RESISTANCE WHEN
IT IS BEING PENETRATED BY ANOTHER BODY.
2. THE CHEMICALS PRESENT IN HEART WOOD AND DENSITY OF WOOD IMPART
HARDNESS TO THE WOOD.
3. THE MERE RESISTANCE OFFERED TO CHISEL OR SAW DOES NOT USUALLY
INDICATE HARDNESS OF WOOD.

12. 5> UNIFORMITY OF PHYSICAL STRUCTURE:-
IT SHOULD BE UNIFORM.
THE FIBERS SHOULD BE FIRMLY ADDED. THE MEDULLARY RAYS SHOULD BE HARD AND
COMPACT. THE ANNUAL RINGS SHOULD BE REGULAR AND THEY SHOULD BE CLOSELY
LOCATED.
THE WOOD SHOULD HAVE A STARIGHT FIBERS.

13. USES OF WOOD:-
THERE IS HARDLY ANY MATERIAL OTHER THAN WOOD WHICH CAN BE USED AS AN
ALL ROUND SUBSTITUTE IN CONSTRUCTIONWORK AND ITS VARIOUS USES CAN BE
SUMMARIZED AS FOLLOWS:
1. IT IS USED FOR DOOR AND WINDOW FRAMES. SHUTTERS OF DOORSAND
WINDOWS, ROOFING MATERIALS. AS A STRUCTURAL MEMBER LIKE BEAM,
COLOUM, ROOF, WALLS ETC.
2. IT IS USED FOR FORMWORK OF CEMENT CONCRETE, CENTERING OF AN ARCH,
SCAFFOLDING, ETC.
3. IT IS USED FOR MAKING FURNITURE, AGRICULTURAL INSTRUMENTS, SPORT
GOODS, MUSICAL INSTRUMENTS, ETC.
4. IT IS USED FOR MAKING RAILWAY COACH WAGONS.
5. IT IS USED FOR MAKING TOYS, ENGRAVING WORKS, MATCHES, ETC.
6. IT IS USED FOR RAILWAY SLEEPERS, PACKING CASES, ETC.
7. IT IS USED FOR TEMPORARY BRIDGES, HOME, SHOPE AND BOAT CONSTRUCTION.

14. Wood is very strong in compression parallel to grain because the wood cells act
as tiny columns or tubes bonded together, giving and receiving support from
neighbouring cells

15. Strength in compression perpendicular to grain is difficult to measure. Compressive
strength increases with deformation, reaching a maximum when the wood is
compressed to about one third of its original thickness.

16. Strength at angle to grain is somewhere between values for parallel and
perpendicular to grain. Formulas and charts are used to determine strength values
for angle to grain loading.

17. Wood is also strong in tension parallel to grain. Knots reduce the strength, but
this is already considered in setting design strength properties.

18. Wood is relatively weak in tension perpendicular to grain. However, it is rarely
required to take much load in that direction except for secondary stresses in
some curved members.

19. For example, tension or compression perpendicular to grain can be induced by
radial stress in curved members.

20. Wood is very strong in bending. Shallow beams have relatively greater resistance to
bending in comparison to proportionately deeper beams. Therefore, depth effect is
considered in setting design properties.

21. Longitudinal or horizontal shear is often a controlling factor in beam design. It is
caused by bending loads, creating maximum longitudinal shear stresses parallel
to grain at the neutral axis.

22. Strength of wood is little
affected by temperatures
and for normal construction
applications is considered to
be the same, from the arctic
to the equator. At low
temperatures, strength
increases slightly. Up to 37°
celcius, strength is hardly
affected, even with
occasional exposures up to
51°. Above that, stresses
should be reduced. In
actual practice, however,
these extremes would
seldom occur.

23. Codes and design standards sometimes require strength values to be adjusted for
preservative treating processes, especially when the wood is incised. Also, when
wood is treated with fire‐retardant chemicals, the design values must be reduced.

24. Thermal expansion of wood is usually insignificant, especially along the grain. For very
long spans, such as in bridges and wood stave pipes, expansion should be
calculated taking the offsetting effect of moisture shrinkage into account.