Question

Define the terms: shear force, bending moment and I-shaped girders.

Short answer

Shear force is a tangential internal force. Bending moment causes bending in a structural element. I-shaped girders are beams with an I-shaped cross-section.

Step-by-step solution

Define Shear Force

Shear force refers to the internal force tangential to the cross-section of a structural element. It arises in response to an externally applied force and acts perpendicular to the axis of the structural element.

Define Bending Moment

A bending moment is the internal moment that causes a beam or structural element to bend. It represents the reaction induced in a structural element when an external force or moment is applied, leading to bending or twisting.

Define I-shaped Girders

I-shaped girders, also known as I-beams, are structural elements characterized by their I-shaped cross-section. They are designed with two horizontal flanges and a vertical web, which provide high strength and stiffness, particularly well-suited for bending and shear forces.

Key concepts

shear force

Shear force is a fundamental concept in structural mechanics that describes the internal force which is tangential to the cross-section of a structural element. It's essential to understand that shear force arises due to external forces acting on the structure. For instance, if you imagine a beam supported at both ends with a load applied in the middle, the shear force is the internal force that resists the external load.

This force acts perpendicular to the length of the beam and attempts to slide one section of the beam past the other. Engineers must calculate shear forces to ensure the structural integrity of buildings, bridges, and other structures. Key points to understand about shear forces:

• Shear forces are typically highest at the supports of a beam.
• They gradually reduce to zero at the midpoint between supports in a simply supported beam.
• Excessive shear forces can cause structural failure, making accurate calculations crucial.

bending moment

Bending moments are crucial in the field of structural mechanics. It refers to the internal moment that causes a structural element, like a beam, to bend. This internal moment is a measure of the rotational forces induced in a structure due to external loads. Imagine a simply supported beam with a load applied in its mid-span; bending moments will develop along the beam as it tries to resist the load.

The maximum bending moment in a beam is often found at its midpoint or where the external load is applied. Understanding bending moments is vital for the design and analysis of structural elements to ensure they can withstand applied loads without failing. Important aspects of bending moments include:

• They cause the beam to bend and can lead to structural failure if not properly accounted for.
• Bending moments are zero at the free end of a cantilever beam or simply supported beam.
• The point of maximum bending moment is critical in design to prevent structural damage.

I-shaped girders

I-shaped girders, also known as I-beams, are integral elements in construction due to their unique shape and high strength-to-weight ratio. The cross-section of an I-shaped girder resembles a capital 'I', consisting of two horizontal flanges connected by a vertical web. This design efficiently handles bending and shear forces, making I-shaped girders ideal for supporting heavy loads over long spans.

The flanges resist most of the bending moment, while the web handles the shear forces. This separation of duties within the I-beam's cross-section enhances its overall structural efficiency. Here are some key characteristics of I-shaped girders:

• The vertical web provides shear strength, preventing the flanges from buckling under compressive forces.
• The horizontal flanges offer resistance against bending, increasing the girder's moment of inertia.
• I-shaped girders are commonly used in bridge construction, building frames, and industrial structures due to their robustness and durability.