Correct Answer: D. 67
Solution:
IS 287: 1993 divides India into four zones for the purpose of timber seasoning based on relative humidity. Zone IV represents the regions with the highest humidity, such as coastal areas. For this zone, the average annual relative humidity is specified as being more than 67%.
Correct Answer: D. Insects
Solution:
DDT is a powerful insecticide. In the past, it was applied to timber as a preservative to protect it from wood-boring insects like termites and beetles. While its use is now heavily restricted due to environmental concerns, its primary purpose in this context was insect prevention.
Correct Answer: B. Rough timber
Solution:
According to IS 399, timber is classified based on its state. Rough timber is the term used for wood that has been obtained after felling a tree. Standing timber refers to living trees, and converted timber is wood that has been sawn into planks, beams, etc.
Correct Answer: B. Conversion
Solution:
These defects are introduced during the process of conversion, which is the sawing of logs into usable timber sections like planks and beams. Chip marks are caused by tools, torn grain by improper sawing, diagonal grain by incorrect alignment of the log, and wane is the presence of the original rounded surface on a piece of sawn timber.
Correct Answer: D. Make it difficult to ignite and support its own combustion
Solution:
Fire-proofing treatments for timber do not make it completely incombustible. Instead, their purpose is to chemically alter the wood so that it becomes difficult to ignite and will not support its own combustion. The treatment creates a char layer or releases non-flammable gases when heated, which inhibits the spread of fire.
1. Coarser grain
2. Widened annular rings
3. Lesser strength
Correct Answer: C. 1, 2 and 3
Solution:
When a tree grows too rapidly, the wood it produces is less dense. This results in widened annular rings and a coarser grain. Because the wood is less dense, it also has lesser strength compared to timber from a slow-growing tree of the same species. Therefore, all three are consequences of rapid growth.
Correct Answer: D. Three or more veneers in odd numbers are placed one above the other with the direction of grains of successive layers at right angles to each other.
Solution:
This statement accurately describes the fundamental construction of plywood. It is always made with an odd number of veneers (3, 5, 7, etc.) so that the grain direction of the top and bottom layers is the same, providing stability. The key to its strength is that the grain of each successive layer is oriented at a right angle (90 degrees) to the previous one.
Correct Answer: C. Heart wood
Solution:
The heartwood is the dense, dark, and non-living central core of a tree trunk. It is composed of the older, inner annual rings and provides the primary structural support. It surrounds the very center, which is the pith.
Correct Answer: C. Grade C
Solution:
As per IS 399, structural timber is graded based on its modulus of elasticity (E). The range of 5.6 to 9.8 kN/mm² falls under the classification for Grade C timber, which is suitable for applications with lower strength requirements.
Correct Answer: B. Conversion of timber
Solution:
Conversion of timber is the process of sawing a felled log into usable commercial sizes like planks, boards, and beams. Felling is the act of cutting the tree down, seasoning is the drying process, and preservation is the treatment to protect it from decay.
Correct Answer: B. 600×50×50 mm
Solution:
The standard size for timber specimens used in durability tests, such as the "graveyard test" where timber is exposed to natural decay conditions, is specified in Indian Standards as 600 mm × 50 mm × 50 mm.
Correct Answer: B. Checks
Solution:
Checks are longitudinal cracks that form across the annual rings, typically caused by uneven drying during seasoning. Shakes, on the other hand, are cracks that run parallel to the annual rings.
Correct Answer: D. Treatment of timber
Solution:
The Bethel process is a full-cell pressure treatment method used for the preservation of timber. It involves placing timber in a sealed cylinder, applying a vacuum to remove air, and then forcing a preservative liquid (like creosote) deep into the wood under high pressure.
Correct Answer: A. Abel's process
Solution:
Abel's process is a specific method for making timber fire-resistant. It involves treating the wood with a solution of sodium silicate (water glass) followed by a treatment with calcium chloride, which forms an incombustible layer on the wood's surface.
Correct Answer: C. Tensile strength is same in all directions
Solution:
The primary advantage of plywood's cross-laminated construction is that it distributes strength more evenly. Unlike solid wood, which is much stronger along the grain, plywood has nearly equal tensile strength in all directions, making it highly resistant to splitting and dimensionally stable.