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Difficulty: MediumCommon Building Materials

When constructing a building framework in an earthquake-prone region, engineers typically choose structural steel over cast iron. Which of the following best explains why structural steel is the superior building material for this specific application?

  1. Structural steel is highly ductile, allowing it to bend and absorb seismic shock without suddenly fracturing.Answer
  2. B
    Structural steel is extremely brittle, which ensures the framework remains perfectly rigid and will not bend during an earthquake.
  3. C
    Structural steel functions exclusively under compression, whereas cast iron is designed to handle the high tension caused by seismic waves.
  4. D
    Structural steel has significantly more mass than cast iron, anchoring the building more firmly to the ground using its own heavy weight.

Answer

Structural steel is highly ductile, allowing it to bend and absorb seismic shock without suddenly fracturing.
Structural steel possesses high ductility, which is a material's ability to undergo significant plastic deformation before rupture. During an earthquake, a building framework experiences extreme and shifting lateral loads. A ductile material like structural steel will bend and yield, safely absorbing the seismic energy without experiencing a sudden, catastrophic fracture. Cast iron, by contrast, is brittle and would crack or shatter under the same dynamic, bending stress.

Step-by-Step Solution

1
Identify the primary forces exerted on a building during an earthquake.
Earthquakes introduce dynamic, unpredictable shocks and vibrations that cause structures to sway, creating rapidly alternating tension, compression, and shear forces.
Understanding the environmental stress is the first step in selecting the appropriate building material.
2
Compare the mechanical properties of structural steel and cast iron under dynamic stress.
Cast iron is hard but brittle, meaning it snaps or shatters under sudden, bending stress. Structural steel is ductile, meaning it can stretch and deform elastically and plastically before failing.
Matching material behavior to the required load type reveals which material will survive the event.
3
Determine which property prevents building collapse during seismic activity.
Ductility is the preferred property because the material absorbs the energy of the earthquake by flexing. A building framework that bends is significantly safer than one that snaps abruptly.
This confirms why structural steel is specifically chosen over brittle alternatives for seismic zones.

Key Concept

Ductility vs. Brittleness in Structural Materials
Estimated Time:45s
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Topics

Common Building Materials

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