What are Flexural Stresses / Bending Stresses

Summary

This video tutorial covers the concept of bending stresses (also known as flexure stresses) in structural engineering, focusing on beams, slabs, and columns. It explains how these stresses occur when a beam is subjected to a uniformly distributed load, causing deflection and creating compressive and tensile stresses. The video also discusses the calculation of bending stresses using a formula involving moment, distance from the neutral axis, and moment of inertia. It highlights how beams are designed for these stresses and the importance of reinforcing them for tension while leaving compression unreinforced due to concrete's strength in compression.

Takeaways

• 😀 Bending stresses (flexure stresses) occur due to the bending of structural members such as beams, slabs, and columns.
• 😀 These stresses are primarily seen in beams, slabs, and retaining walls, which are designed to withstand these stresses.
• 😀 A simple example is a simply supported beam subjected to a uniformly distributed load, which causes bending and deflection.
• 😀 The maximum bending stresses occur at the top and bottom of the beam, with zero stress at the neutral axis.
• 😀 Bending stresses are classified into compressive and tensile stresses, depending on the location within the beam.
• 😀 Compressive stresses are found at the top of the beam, while tensile stresses are found at the bottom of the beam.
• 😀 The neutral axis of the beam is the point where there are zero stresses.
• 😀 The formula for calculating bending stresses is: σ = M * y / I, where M is the moment, y is the distance from the neutral axis, and I is the moment of inertia.
• 😀 Maximum bending stresses occur at the top and bottom of the beam, with the highest stress being at the maximum distance from the neutral axis.
• 😀 Concrete is strong in compression and weak in tension, so reinforcement is added to the bottom of beams to resist tensile stresses, while compression does not require reinforcement.

Q & A

What are bending stresses in structural members?

Bending stresses, also known as flexural stresses, occur when a structural member like a beam bends due to an applied load. These stresses are most commonly found in beams, slabs, and retaining walls.

Why do bending stresses occur in beams?

Bending stresses occur because when a load is applied to a beam, it deflects. The supports resist the deflection, which results in compression at the top of the beam and tension at the bottom.

What is the neutral axis in a beam?

The neutral axis is the point in the beam where there is zero bending stress. It lies between the areas of compression at the top and tension at the bottom of the beam.

How are compressive and tensile stresses distributed in a beam?

In a beam under bending, compressive stresses occur at the top of the beam, while tensile stresses occur at the bottom. The neutral axis, located in the middle, experiences no stress.

How do you calculate bending stresses in a beam?

Bending stresses are calculated using the formula: σ = M * y / I, where M is the bending moment, y is the distance from the neutral axis to the point of interest, and I is the moment of inertia of the beam's cross-section.

What is the moment of inertia, and how is it calculated for a rectangular beam?

The moment of inertia (I) is a property of the beam's cross-section that describes its resistance to bending. For a rectangular beam, it is calculated as I = b * h³ / 12, where b is the width and h is the height of the beam.

What are the two main types of stresses in a bending beam?

The two main types of stresses are compressive stresses, which occur at the top of the beam, and tensile stresses, which occur at the bottom.

Why does concrete need reinforcement at the bottom of beams?

Concrete is strong in compression but weak in tension. Therefore, reinforcement is added at the bottom of the beam to resist the tensile stresses and prevent cracking.

What is the significance of the neutral axis in bending stress calculations?

The neutral axis is important because it marks the point where the bending stress is zero. It helps in determining the distribution of compressive and tensile stresses in the beam.

What is the relationship between the location of the neutral axis and the bending stresses?

The location of the neutral axis determines the distribution of bending stresses. The further you move from the neutral axis, the greater the bending stress, with maximum stresses at the top and bottom of the beam.