The GATE Grind

GATE 2018 ME (ME2) – Question 18

Machine Design · Bolted, riveted and welded joints · 1 mark · Multiple choice

Pre-tensioning a bolted joint is used to ______.

  1. strain harden the bolt head
  2. decrease stiffness of the bolted joint
  3. increase stiffness of the bolted joint
  4. prevent yielding of the thread root

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Correct answer: (C) increase stiffness of the bolted joint

Explanation

Pre-tensioning clamps the joint members together with a force larger than the external working load. While this clamp force is not overcome, the members stay in contact, so the joint behaves as a stiff continuous body and the external load changes the bolt load only slightly.

The purpose of pre-tension is therefore to **increase the stiffness of the bolted joint, C**.

It does not reduce stiffness, it does not strain-harden the bolt head, and thread-root yielding is a strength check rather than the reason for pre-tension.