Calculate Dimensions of a Rectangular Beam - 8280Nm, 36cm^3, 230MPa

In summary, the conversation is about calculating the dimensions of a solid rectangular beam with a given maximum bending moment, section modulus, and allowable stress. The formula for calculating the section modulus is discussed, but the individual is unsure how to proceed with finding the dimensions from the given information. They are given a second equation relating the base and height of the beam and are reminded that they now have two equations and two unknowns.
  • #1
mm391
66
0
Hi,

Calculate the dimensions of a solid rectangular beam using the information below:

Max Bending Moment= 8280Nm

Ze = 36cm^3

Allowable Stress = 230MPa

d = 2b

Stress = moment/section modulus
 
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  • #2
Where are your workings? Where is it you're having problems?
 
  • #3
TaxOnFear said:
Where are your workings? Where is it you're having problems?

Sorry I did this on my phone and I didn't have time to finish it.

I have the following:

230 = 8280/36cm^3 The problem I have is am not sure where or how to go about finding the dimensions from here.
 
Last edited:
  • #4
what's the section modulus formula for a rectangular beam?
 
  • #5
Z= I/y with y being depth/2.

But I can't see how this will help. Sorry.
 
  • #6
mm391 said:
Z= I/y with y being depth/2.

But I can't see how this will help. Sorry.
Yes, Z= I/(d/2), so what is I in terms of the base (b) and height (d), for a rectangular cross section?
 
  • #7
Firstly thank you for your help and patience.

PhanthomJay said:
Yes, Z= I/(d/2), so what is I in terms of the base (b) and height (d), for a rectangular cross section?

((b*d^3)/(d/2) = b*d^2/6

Z = b*d^2/6

Z * 6 = b*d^2

But I still have two unknowns and one equation.
 
  • #8
mm391 said:
Firstly thank you for your help and patience.



((b*d^3)/(d/2)
you mean (bd^3/12)/(d/2) = b*d^2/6
Z = b*d^2/6

Z * 6 = b*d^2

But I still have two unknowns and one equation.
No, you have 2 unknowns and 2 equations...the one that was given you...in your original post..

d = 2b
 

1. How do I calculate the dimensions of a rectangular beam given the values of 8280Nm, 36cm^3, and 230MPa?

To calculate the dimensions of a rectangular beam, we will need to use the formula F = M*y/I, where F is the force (in Newtons), M is the bending moment (in Newton-meters), y is the distance from the neutral axis to the outermost fiber (in meters), and I is the moment of inertia (in meters^4). We can rearrange this equation to solve for y, which will give us the height of the beam. Then, we can use the formula V = (b*h^2)/6, where V is the volume (in cm^3), b is the width of the beam (in cm), and h is the height of the beam (in cm). Finally, we can use the formula σ = M*c/I, where σ is the stress (in MPa), c is the distance from the neutral axis to the centroid (in meters), and I is the moment of inertia (in meters^4). We can rearrange this equation to solve for c, which will give us the distance from the neutral axis to the centroid. Once we have the height, width, and distance from the neutral axis to the centroid, we can calculate the remaining dimensions of the rectangular beam.

2. What is the moment of inertia, and how does it affect the dimensions of a rectangular beam?

The moment of inertia is a measure of an object's resistance to changes in its rotational motion. In the context of a rectangular beam, it is a measure of how the beam's cross-sectional area is distributed around its neutral axis. The larger the moment of inertia, the more resistant the beam will be to bending. Therefore, a larger moment of inertia will result in smaller dimensions for a given bending moment, as the beam will be able to withstand the force more easily.

3. How does the bending moment affect the dimensions of a rectangular beam?

The bending moment is the force that causes a beam to bend or flex. In order to withstand this force, the dimensions of a rectangular beam must be large enough to distribute the force and prevent the beam from breaking. A larger bending moment will require larger dimensions for the beam in order to maintain its structural integrity.

4. Is there a limit to the dimensions of a rectangular beam, and how can I determine the appropriate dimensions for a given application?

There is no hard and fast rule for the maximum dimensions of a rectangular beam. The appropriate dimensions will depend on various factors such as the load, the material of the beam, and the structural requirements of the application. To determine the appropriate dimensions, it is best to consult with a structural engineer who can analyze the specific requirements and provide a suitable design for the beam.

5. Can I use these calculations for other beam shapes, such as a circular or triangular beam?

The calculations for determining the dimensions of a rectangular beam are specific to its shape. Other beam shapes, such as circular or triangular, will have different formulas and considerations for calculating their dimensions. It is important to use the appropriate formulas and consult with a structural engineer for the design of any type of beam.

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