Why use I beams in construction? | Class 11 (India) | Physics | Khan Academy

Summary

This video explores the significance of I-beams in engineering, particularly their design and functionality in structures like bridges. The I-beam, shaped like the letter 'I', efficiently resists bending forces while minimizing material use. As loads cause bending, different stresses—compressive on the top and tensile on the bottom—are generated. Engineers optimize the I-beam design by thickening the areas under stress and removing unnecessary material from the center. This innovative approach ensures strength without increasing weight, making I-beams a preferred choice for durable and effective construction.

Takeaways

• 😀 The I-beam gets its name from its cross-sectional shape resembling the capital letter 'I.'
• 😀 Engineers prefer I-beams because they effectively resist bending forces in structures.
• 😀 Bending occurs in beams due to external forces like gravity and loads from vehicles.
• 😀 When a beam bends, the top part experiences compressive stress while the bottom part experiences tensile stress.
• 😀 Increasing the thickness of a beam can resist bending but also increases weight, creating further challenges.
• 😀 Engineers aim to make beams thicker where stress is maximum without adding unnecessary weight.
• 😀 The center of a beam does not experience stress, making it possible to remove material from that area.
• 😀 Removing material from the center and adding it to the top and bottom results in the efficient I-beam design.
• 😀 The I-beam's design allows for maximum strength while minimizing material usage and weight.
• 😀 I-beams are considered the most efficient shape for withstanding bending in structural applications.

Q & A

What is the most common shape of beams used in structures?

The most common shape of beams is the I-beam, named for its cross-section that resembles the capital letter 'I.'

Why do engineers prefer the I-beam shape over other shapes?

Engineers prefer the I-beam shape because it is structurally efficient in resisting bending and managing stress without using excessive material.

What forces act on a bridge that can cause deformation?

Forces such as gravity, which pulls down on the bridge due to its own weight, and the weight of vehicles or other loads on the bridge contribute to deformation.

What happens to a beam when it deforms under stress?

When a beam deforms under stress, it experiences compression in the upper part and tension in the lower part, which can lead to potential failure if the stress exceeds material limits.

How does increasing the thickness of a beam affect its bending resistance?

Increasing the thickness of a beam generally makes it harder to bend because it adds more material, which provides greater resistance to bending forces.

What problem arises when simply making a beam thicker to resist bending?

Making a beam thicker increases its weight, which can lead to increased bending forces, creating a cycle of problems rather than solving them.

What types of stresses are generated in a bent beam?

A bent beam generates compressive stress at the top (where molecules are closer together) and tensile stress at the bottom (where molecules are farther apart).

Where is stress maximum in a bent I-beam?

Stress is maximum at the top and bottom of the I-beam, where compression and tension occur, respectively; there is minimal to no stress at the center.

Why is material removed from the center of an I-beam?

Material is removed from the center of an I-beam because it does not contribute to bending resistance, allowing for a more efficient use of material while maintaining structural integrity.

What is the significance of the I-beam design in engineering?

The I-beam design is significant because it allows engineers to create strong, lightweight structures that efficiently withstand bending, making it an ideal choice for various construction applications.