Question

Timber as a building material:

• A. Has more tensile strength than steel
• B. Is preferred due to high compressive strength and flexibility
• C. Lower strength-to-weight ratio compared to concrete
• D. Exhibits maximum strength perpendicular to the grain

Hint:

Timber is an anisotropic material:
• Parallel to Grain: High strength (best for columns and beams).
• Perpendicular to Grain: Low strength (susceptible to splitting).

Answer 1

The Correct Option is B

Concept: Timber is a natural, anisotropic organic material used structurally in architectural engineering. Its mechanical properties vary depending on the orientation of its wood fibers (grains). It provides an excellent balance of compressive resistance, bending flexibility, and weight efficiency.

Step 1: Analyzing the mechanical performance of structural wood.
Let us evaluate why structural timber remains highly valued for framing and trusses, validating Option B:
• High Compressive Strength: When loaded parallel to its grain fibers, timber functions efficiently as a column, supporting significant structural loads.
• Flexibility and Elasticity: Wood fibers can bend and absorb kinetic energy without sudden, brittle failure. This flexibility makes timber structures resilient in earthquake-prone regions, as the joints and fibers can deflect and return to their original shape.

Step 2: Identifying errors in the alternative statements.

• Option A: Steel has a significantly higher ultimate tensile strength ($250\text{--}500\text{ MPa}$) compared to structural timber ($40\text{--}100\text{ MPa}$).
• Option C: Timber actually has a *higher* strength-to-weight ratio than standard plain concrete. Because it is lightweight, a timber beam can support its own weight more efficiently over a span than a heavy, unreinforced concrete beam.
• Option D: Timber is highly anisotropic. It exhibits its minimum structural strength when forces are applied perpendicular to the grain, as perpendicular forces can split or crush the parallel fiber bundles easily. Maximum strength is achieved parallel to the grain.