Timber MCQ Quiz in తెలుగు - Objective Question with Answer for Timber - ముఫ్త్ [PDF] డౌన్‌లోడ్ కరెన్

Solution:

Shakes are nothing but cracks that separate the wood fibers partly or completely. Different shakes are formed in different conditions as follows:

Cup shakes: 

• They are formed due to the non-uniform growth of a tree or excessive bending by cyclones or winds. In this case, the shakes develop between annual rings and separate them partly. 
• As such, when fully developed, they may separate portions of timber longitudinally along the rings. But this condition is seldom seen.
• Generally, they develop along a part of a particular annual ring. Reasons for the development of cup or ring shakes are to be sought in the unequal growth of timber.

Heart shakes:

• The other type of shakes develops in maturity approaching trees whose inner part is under shrinkage.
• The shake spread from pith to sapwood following the directions of medullary rays. These are cracks or clefts occurring in the heartwood, i.e., towards the inner region. 
• They become thinner as they extend outward (towards sapwood).

Ring shake:

• They are similar to cup shakes, but they completely separate the annual rings.

Star shakes:

• They are also called radial shakes. They generally arise in the sapwood and extend towards the inner regions.
• The main cause for their development in a living tree is severe temperature differences during different seasons, such as excessive heat during summer, and severe cold, leading to frost formation in winter. 
• They develop wider cracks on the outside of timber from bark to sapwood. They indicate the beginning of the decay of the tree.

1. Pith: It is the innermost part of the tree that consists of cellular tissue which is used for nourishment of the tree at a young age.

2. Sapwood: It is the outer annual ring between heartwood and cambium layers. It is the living, outermost portion of a woody stem or branch.

3. Heartwood: It is the dead, inner wood, which often comprises the majority of a stem's cross-section.

4. Cambium Layer: It is a thin layer of sap between sapwood and inner bark.

Explanation:

The defect arises due to conversion of timber:

Chip mark, Torn grain, Diagonal grain, and wane.

The defect arises due to Fungi:

Heart rot, Brown rot, Dry rot, Sap stain, and Blue stain.

Defects arises due to Natural forces:

Cup shakes, Ring shakes, Heart shakes, Star shake, and radial shake.

Defects arise due to Seasoning:

Bow, warp, cup, and Twist.

The timber shows high strength in the direction parallel to grains.

Compressive strength along grain > Compressive strength across grain

Tensile strength along grain > Tensile strength across grain

Note:

Tensile strength along grain is 2 to 4 times Compressive strength along grain.

Explanation:

Timber:

• Timber is sawn or milled wood used for engineering purposes like building, furniture, and railway track wooden sleeper construction.

Classification of the tree: 

For engineering purposes, the trees are classified according to their mode of growth.

Endogenous tree:

• These trees grow inwards.
• Timber from these trees has very limited engineering applications.
• Examples of endogenous trees are bamboo, cane, palm, etc.

Additional Information

Exogenous tree:

• These trees grow outwards, increasing in bulk with the formation of the ring every year.
• These annual rings are used for predicting the age of the tree.
• These trees are mostly used for engineering work.
• They are further divided into conifers and deciduous.

Conifers (Evergreen trees):​​

• The leaves of these trees do not fall till new ones are grown. These have needle-shaped leaves and bear cone-shaped fruits.
• These trees yield softwood (easily cut), which is generally light-colored, resinous, lightweight, and weak.

• They have distinct annual rings. Example: deodar, pine, fir, and larch

Deciduous or broad-leaf trees:

• These trees have flat broad leaves. The leaves of these trees do not fall till new ones appear in the spring season.
• They do not show distinct annual rings.
• These trees yield hardwood, which is generally close-grained, strong, heavy, dark-colored, durable, and nonresinous; and are used for engineering applications.
• Examples: teak, mahogany, Sheesham, oak, sal, babool, etc.

Uncontrolled and non-uniform loss of moisture causes warping in the timber.

Defect arises due to conversion of timber:

Chip mark, Torn grain, Diagonal grain and wane.

Defect arises due to Fungi:

Heart rot, Brown rot, White rot, Dry rot, Wet rot, Sap stain and Blue stain.

Defects arises due to Natural forces:

Cup shakes, Ring shakes, Heart shakes, Star shake and radial shake.

Defects arises due to Seasoning:

Bow, warp, cup and Twist.

Explanation:

Defects in timber due to natural forces:

The main natural forces are responsible for causing defects in timber are abnormal growth and rapture of tissues.

Burls:

• Irregular projections appear on the body of timber because of shock at younger age.

Callus:

• A soft tissue which covers the wound of the tree.

Chemical stain:

• The chemical activity triggered discoloration.

Coarse grain:

• Annual rings are widened; the tree grows quickly and thus timber has less strength.

Dead wood:

• Wood harvested from standing dead trees.

Druxiness:

• White decayed spots by fungi.

Foxiness:

• Due to poor ventilation during storage or by the commencement of decay due to over maturity indicated in wood by red or yellow tinge.

Knots:

• Branch bases that are split, or cut off from the tree.

Rind galls:

• Rind means bark and gall is indicated abnormal growth and peculiarly curved swellings found on the body of a tree.

Shakes:

• These are cracks which completely separate the fibers of the wood.

Twisted fibers:

• As the name indicate it’s caused by the twisting of young trees by fast blowing wind it's also known as wandering hearts.

Upsets or ruptures:

• It shows wood fibers that are damaged by compression or crushing.

Sir Abel’s Process: The surface of the timber is first painted with a weak solution of sodium silicate. Thereafter slaked fat lime solution of followed by a concentrated solution of silicate of soda. This makes timber fire-resistant.

Points to Remember:

The fire resistance of timber can be enhanced by phosphates of ammonia, a mixture of ammonium phosphates and ammonium sulphate, borax and boric acid, sodium arsenate etc.

White ant affects the lignin (tissue) part of the timber section due to which it assumes white color and hence, also called white rot.

Among all the given wood, teak is hardwood i.e. it has strongest tissues and hence, offers maximum resistance against white ants or termites.

Note: Teak instead of resisting termites it actually kills the white ants.

Important Points:

The most timber is obtained from teak because it has the following properties:

1. Wood obtained from it is hard and strong and not resinous.

2. All woods contain oil (sap wood). Teak can retain these oils even after being felled and processed. Because of this, teak has greater weather-resistant properties.

3. Resistance against white ants.

4. It is durable and fire-resistant.

5. It does not allow the corrosion of iron fastenings.

6. Seasoning of teak wood is very easy and it is easily workable.

Concepts:

S1 True

The Fiber Saturation Point (FSP) in wood is the stage where the cell walls are fully saturated with water, but the cell lumens are empty. Below this point, typically around 25-30% moisture content, changes in moisture content can affect the wood's mechanical properties like strength, stiffness, and hardness. However, up to this point, the mechanical properties are not materially affected as the water is only being removed from the cell lumens and not the cell walls.

S2: False

Shrinkage in wood takes place due to a reduction in moisture content. This reduction takes place in directions perpendicular to the grain only, while a much smaller change takes place along the length. The experimental results show that wood shrinks and swells the greatest amount in the tangential direction, about half as much in the radial direction, and about 0.1% to 0.2% in the longitudinal direction.