Plastic Analysis MCQ with answer and solution

Concept

Role of plastic hinges in moment redistribution

Formula

M_p = Z_p × f_y

Step-by-step solution

1. A plastic hinge forms when a section reaches its full plastic moment capacity Mp throughout the depth. 2. Once formed, the cross-section maintains its moment capacity while undergoing inelastic plastic rotation. 3. Continued loading causes additional moments to be absorbed by adjacent elastic regions of the indeterminate structure. 4. Therefore, plastic hinges primarily facilitate moment redistribution throughout the structure. Answer: C

Explanation

In ductile structural design, the formation of plastic hinges at peak moment regions allows large plastic rotations at constant resisting moment. This ductile behavior enables the redistribution of moments to less heavily stressed adjacent sections, preventing sudden collapse.

Why the other options are wrong

A) Plastic hinges form due to high bending moments, not pure compression transfer. B) Plastic hinges are yield zones with ductility, not points of catastrophic failure. D) Plastic hinges do not reduce incoming earthquake ground motion loads directly.

Shortcut

Plastic hinge = Yield mechanism that allows moment redistribution before collapse.

Common mistake

Believing plastic hinges indicate structural collapse or failure rather than energy-absorbing ductility.