Design of Tension Members MCQ with answer and solution

Concept

Valid tensile tests of steel reinforcement bars require failure within the gauge length; failure in the gripping section indicates localized stress concentrations due to improper machine alignment or jaw clamping.

Step-by-step solution

1. Understand the standard procedure for tensile testing of steel rebar as per IS 1608. 2. Note that the gauge length is marked in the central portion of the specimen where uniform stress is expected. 3. Identify that failure occurring inside the grips indicates stress concentration or bending moments introduced by improper gripping alignment rather than true material tensile strength.

Explanation

During the tensile testing of a rebar or steel specimen, the failure should ideally occur within the gauge length in the middle portion of the specimen. If the failure occurs in or very close to the gripping section (jaw/collet area), it usually indicates stress concentrations caused by improper gripping alignment, slippage, or jaw crushing, rendering the test invalid according to standards like IS 1608 / ASTM E8.

Why the other options are wrong

A: Material brittle failure would typically show a clean break with little reduction in area, but within the gauge length. C: High elongation is a ductile property measured across the gauge length after a valid test. D: High tensile strength is an inherent material property, not a cause for grip failure.

Shortcut

Grip failure = Machine/Alignment issue (invalid test). Middle failure = Material property (valid test).

Common mistake

Assuming that a failure in the grips means the material has low tensile strength.