STD MODULE 1 - Introduction to Timber

Timber

- One of the oldest known materials used in construction

- Can be highly durable when properly treated and built

- Easiest to construct

- Homogenous material

Timber → Reinforced Concrete → Steel

Rank the materials based on affordability, from least expensive to most expensive:

(Timber, Steel, Reinforced Concrete)

Timber → Steel → Reinforced Concrete

Rank the materials based on durability, from least durable to most durable:

(Timber, Steel, Reinforced Concrete)

Timber → Steel → R.C.

Rank the materials based on availability, from least available to most accessible:

Timber, Steel, Reinforced Concrete

1) Natural Defects

2) Chemical Defects

3) Conversion Defects

4) Seasoning Defects

Defects in Timber

Natural Defects

These type of defects occur during the growing period

a) Cracks and Fissures

b) Knots

c) Annual Ring Width

d) Fungal Decay

e) Grain Defects

Examples of Natural Defects

a. Straight-grain / Flat-grain(?)

b. Irregular-grain

c. Diagonal-grain

d. Spiral-grain / Twisted-grain

e. Interlocked-grain / Cross-grain (?)

f. Wavy-grain

Types of Grain Defects

Cracks and Fissures

They may occur in various parts of the tree

may even indicate the presence of decay or the beginnings of decay

Knots

- These are common features of the structure of wood.

- A portion of a branch embedded by the natural growth of the tree, normally originating at the center of the trunk or a branch

Annual Ring Width, reduce

Excess _______ of such rings can ____________ (increase/reduce) the density of the timber

Fungal Decay

- may occur in growing mature timber or even in recently converted timber

- in general it is good practice to reject such timber

Grain Defects

- Refers to the general direction of fibers in wood.

- All types can induce subsequent problems of distortion in use

Straight grain

Type of grain in which the fibers in a board run roughly parallel with the vertical axis of the log from which it was sawn.

Irregular Grain, knots

The wood fibers run at varying directions from the vertical axis of the log, such as around _______

Diagonal Grain

This type of grain results when an otherwise straight-grained log isn't sawn along its vertical axis

Spiral Grain

When trees grow twisted, this type of grained logs and subsequent boards are produced, where fibers follow with either left or right hand twist.

Interlocked grain

Grains are in successive layers and in opposite direction

Wavy Grain

When the direction of the wood fibers constantly changes

Chemical Defects

These may occur in particular instances when timber is used in unsuitable positions or in association with other materials.

Conversion Defects

Basically due to unsound practice in the use of milling techniques or to undue economy in attempting to use every possible piece of timber converted from the trunk.

Examples: wane, chip mark, diagonal grain

wane, chip mark, diagonal grain

Examples of Conversion Defects

Seasoning Defects

- Movement that occurs in timber due to changes in moisture content.

- Excessive or uneven drying

- Exposure to wind and rain

- Poor stacking and spacing

- Such defects have an effect on structural strength as well as on fixing, stability, durability and finished appearance.

1. cupping

2. end splitting

3. honeycombing

4. springing

5. bowing

6. twisting

Examples of Seasoning Defects

1. Air Drying

2. Sun Drying

3. Kiln Drying

Methods of Wood Drying

Softwoods and Hardwoods

Types of TImber

Softwoods

Quick Growth Rate

Generally Poor Durability

Readily available and comparatively cheap

Hardwoods

Slower Growth Rate

Less dependent on preservatives for durability

Expensive

1. Moderately Low Strength Group: Raintree, Bayok, Almaciga

2. Medium Strength Group: Pine, Apitong, Lauan

3. Moderately High Strength Group: Narra, Guijo, Mahogany

4. High Strength Group: Molave, Yakal, Agoho, Liusin, Narig

Types of Timber Compiled by Forest Products Research and Development Institute (FPRDI)

1. Moisture Content

2. Density

3. Slope of Grain

Physical properties of Timber

1. T

2. 17-23% (air dried)

3. shrinkage, loss of strength

Moisture Content:

1. T/F: Dependent on local conditions

2. Generally b/n ____________

3. Too little will result in __________, too much will result in _________________

1. T

2. Solid substance

3. Oven-dried weight : Weight of equal volume of water

4. 0.29 to 0.81

5. 0.35 - 0.60

Density

1. T/F: Density is the best indicator of strength

2. Density is the measure of _____________

3. It is the Ratio of ______________ to _____________

4. The ratio ranges from __________________

5. Tha ratio most falls b/n ____________

1. Longitudinal direction

2. Bending Resistance

3. Axial Resistance

Slope of Grain:

1. Slope of grain is the _______________ of the main elements

2. Deviation to the longitudinal axis leads in a significant drop in _____________________

3. Slope of grain does not affect _________________

1. Dressed

2. Rough Sawn

3. Full Sawn

Sizes of Timber

7 1/2 x 11 1/2

Dressed Size

7 5/8 x 11 5/8 (1/8" larger than dressed size)

Rough Sawn Size

8 x 12

Full Sawn Size

Board Foot ( 1bd. ft. = T" x W" x L' / 144 )

What measures the Timber Volume

8 board feet

How many board feet?

A 2-inch thick, 6-inch wide, and 8-foot long piece of lumber:

too little leads to shrinkage, while too much results in loss of strength.

What is the relationship between moisture content and timber strength?

The Slope of Grain affects bending resistance significantly, with deviations leading to reduced strength.

What is the significance of the Slope of Grain in timber?

Measure of timber volume equivalent to 144 cubic inches.

What is a Board foot in timber measurement?