# Beam Design

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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Where are your workings? Where is it you're having problems?

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:
PhanthomJay
Homework Helper
Gold Member
what's the section modulus formula for a rectangular beam?

Z= I/y with y being depth/2.

But I can't see how this will help. Sorry.

PhanthomJay
Homework Helper
Gold Member
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?

Firstly thank you for your help and patience.

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.

PhanthomJay
Homework Helper
Gold Member
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