Bridge Engineering MCQ with answer and solution

Concept

Functions and mechanism of knuckle bearings

Formula

NONE

Step-by-step solution

1. The question specifies a bearing that provides 'only for angular movement of the girder which is fixed to the top shoe'. 2. Fixed bearings permit angular rotation due to bending deflection while restraining longitudinal translation. 3. A knuckle bearing features a top shoe fixed to the girder and rocks on a knuckle or pin, allowing only angular rotation. 4. Therefore, option C (Knuckle Bearing) is correct. Answer: C

Explanation

A knuckle bearing is a fixed bridge bearing designed to permit angular rotation of the girder caused by deflection under live loads, while preventing horizontal translation. The girder is securely fixed to the top shoe, which articulates against the bottom shoe across a cylindrical pin or curved knuckle surface.

Why the other options are wrong

A) Expansion bearings permit horizontal expansion/contraction as well as rotation. B) Rocker bearings are typically paired with rollers at the free end to allow longitudinal movement. D) Sliding bearings facilitate horizontal displacement via sliding plates.

Shortcut

Knuckle Bearing = Like an anatomical knuckle joint (allows rotation/angle only, no translation).

Common mistake

Selecting Rocker Bearing or Expansion Bearing, which are designed to allow horizontal expansion and translation along the bridge span.