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Question

Difficulty: MediumTypes of Stress and Strain

A worker stands on the top platform of an open A-frame stepladder resting on a smooth floor. The ladder has a horizontal folding metal spreader bar that connects the front and rear legs to keep the ladder from collapsing flat. What primary type of internal stress is experienced by the horizontal spreader bar while supporting the worker's weight?

  1. TensionAnswer
  2. B
    Compression
  3. C
    Shear
  4. D
    Torsion

Answer

Tension
When a downward load is applied to an A-frame ladder, the angled legs tend to spread outward. The horizontal spreader bar counteracts this by holding the legs together. Because the legs pull outward on both ends of the bar, the bar experiences a pulling force along its length. A force that pulls or stretches a material is defined as tension.

Step-by-Step Solution

1
Analyze the external forces acting on the ladder.
The downward force (worker's weight) pushes the ladder into the ground.
To determine how the entire structure distributes the load.
2
Determine the direction of movement the legs would take without the spreader bar.
The downward weight causes the angled front and rear legs to try to splay or slide outward away from each other on the smooth floor.
Understanding the tendency of movement reveals what the supporting member must resist.
3
Identify the opposing force exerted by the spreader bar.
The spreader bar must hold the legs together, meaning it is being pulled outward from both ends by the spreading legs.
Identifying the force acting on the component determines the type of stress.
4
Classify the internal stress based on the pulling force.
A pulling force acting along the longitudinal axis of a member creates tensile stress (tension).
This matches the definition of tension.

Key Concept

Identifying tension in structural members resisting outward forces
Estimated Time:45s
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Topics

Types of Stress and Strain

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