Beam stiffness is the ability of a beam to resist bending when a bending moment is applied. It is influenced by the material and shape of the cross section. The stiffness can be calculated using the elastic modulus and moment of inertia. The I-beam is a common design in civil engineering due to its high area moment of inertia and steel material.
In structural engineering, beam stiffness is the ability of a beam to resist bending, or bending, when a bending moment is applied. A bending moment occurs when a force is applied somewhere in the middle of a beam that is fixed at one or both ends. It will also occur if a torque is applied to the beam, although this is less common in real world applications. The stiffness of the beam is influenced by both the material of the beam and the shape of the cross section of the beam.
The rationale for designing a beam that resists bending is easy to appreciate in the case of a bridge. For example, concrete is great for its compressive strength, but a bridge made entirely of concrete would be a poor choice. Concrete is not strong when bent; a concrete bridge will sag in the middle due to gravity and probably fall apart. The bridge could be much stronger if it had some sort of foundation, or skeleton, to keep it from veering too far in between.
The stiffness of the beam can be calculated using two factors. The first factor is the elastic modulus. This is a material property that refers to the material’s tendency to deform, or stretch, when a stress is applied. If the beam is made of stainless steel, it will have a higher elastic modulus than, for example, aluminium. This is because if the same forces are applied to the same shape of steel and aluminum, the steel object would deform less. While metals don’t deform as much as rubber bands do, they do the same; they stretch in proportion to the force with which a force pulls them. Thus, a beam made of a material with a high modulus of elasticity will have a high stiffness of the beam, making it less prone to bending.
The other factor of the beam stiffness is the moment of inertia of the cross sectional area of the beam. This has to do with the vertical distribution of material near or away from the center of the beam. A beam design often used in civil engineering with a high area moment of inertia is the I-beam. It is called I-beam because of its cross section, which is shaped like the letter ‘I’. This shape concentrates much of the material towards the bottom and top of the cross section with only enough material in the central regions to connect the outer parts. The reason for this shape is that it maximizes the moment of inertia of area for a given amount of material. The most common material used in I-beams is steel, which provides a high elastic modulus. These two properties of the I-beam give it a very high beam stiffness.
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