Second moment area of symmetrical shape

In summary, the discussion revolves around the second moment area (I) for a beam with a rotated square cross section. The question is whether the formula I=b^4/12 (cube) can be applied to this shape or if an alternative method, such as using the formula for a triangle and the parallel axis theorem, should be used. The relevance of the integral I=integral(r^2dr) is also questioned.
  • #1
fosternn
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0

Homework Statement



-a beam with square cross section, side lengths bXb is rotated 45 degree.
-can we assume the second moment area (I) is the same if this is done?

Homework Equations



I=b^4/12 (cube)
I=integral(r^2dr)

The Attempt at a Solution

 
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  • #2
If you know how the formula I=b^4/12 (cube) has been derived from an integral, then you should be able to do the same for the diamond shape. Or, if you accept the formula for a triangle and apply the parallel axis theorem, you can answer the question yourself. I don't see the relevance of I=integral(r^2dr).
 

1. What is the second moment area of a symmetrical shape?

The second moment area, also known as the moment of inertia, is a property of a symmetrical shape that measures its resistance to bending or twisting. It is a measure of the distribution of mass around an axis and is calculated by integrating the square of the distance from the axis of rotation for all points on the shape.

2. How is the second moment area calculated?

The second moment area is calculated by multiplying the area of each element of the shape by the square of its distance from the axis of rotation. These values are then summed together to get the total moment of inertia for the shape.

3. What is the significance of the second moment area in engineering?

The second moment area is an important property in engineering as it determines the amount of stress and deflection a structure will experience when subjected to a bending moment. It is also used in the design of beams, columns, and other structural elements to ensure they can withstand the loads placed upon them.

4. How does the second moment area differ for different symmetrical shapes?

The second moment area varies depending on the shape and distribution of mass around the axis of rotation. For example, a hollow circular tube will have a higher moment of inertia than a solid circular rod of the same outer diameter due to the greater distribution of mass further from the axis of rotation in the tube.

5. Can the second moment area be used to determine the strength of a material?

No, the second moment area is not directly related to the strength of a material. It is a geometric property of a shape and does not take into account the material properties. The strength of a material is determined by its yield strength, ultimate tensile strength, and other material properties.

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