Design of Tension Members MCQ with answer and solution

Concept

Rods and bars carry tension well, but they are very flexible because their radius of gyration is small.

Formula

λ = L/r_min; for a round rod r = d/4

Step-by-step solution

1. Rods and bars are solid sections with a small cross-section. 2. Their radius of gyration r is small, so the slenderness ratio L/r is high. 3. A high L/r means low stiffness. The rod sags under its own weight and can vibrate or rattle. 4. Tensile strength is the main reason we use rods in tension. It is an advantage, not a disadvantage. 5. So the answer is (B).

Explanation

Rods and bars are good at carrying tension, so tensile strength is their advantage. Their problems are low stiffness, high slenderness ratio and sag under self-weight. So tensile strength is NOT a disadvantage.

Why the other options are wrong

A: Inadequate stiffness is a real disadvantage because the rod is flexible. C: Sag under own weight is a real disadvantage, mainly in long horizontal rods. D: High slenderness ratio is a real disadvantage because r is small.

Shortcut

In a NOT question, pick the option that is a strength of the member: tensile strength.

Common mistake

Reading the question as 'which is a disadvantage' and missing the word NOT.