Max Bending Stress: Find from Second Moment of Area

[Simon green]

Homework Statement

The second moment of area of the beam shown about the neutral axis X X is 4x10^6mm^4

Find the maximum bending stresses, tensile and compressive, set up in a beam of this section 2.6m long and simply supported at its ends and carrying a concentrated load of 4.8kn at its mid point, the weight of the beam may be ignored

Unable to load the picture of this beam, it is a t shaped beam with the neutral axis XX running through the centre of the beam horizontally and 40mm from the top of the beam, it also has an overall height of 120mm

Homework Equations

M/I = E/R = σ/y

The Attempt at a Solution

As far as I am aware I need to use σ/y = m/I to find the correct answer, y = 40mm (distance from neutral axis)
I= 4x10^6mm^4 (second moment of area)
I am unsure about which values or how to work out either σ or m

 

[PhanthomJay]

You have the right equation and you are trying to find the bending stress. The value of I is given. Please let us know what is your understanding of y and m in your equation.

 

[Simon green]

I believe that y is the distance from the neutral axis (40mm) and m is the maximum bending stress? But m is not given is it? Do I have to transpose the formula to find m?

 

[PhanthomJay]

I believe that y is the distance from the neutral axis (40mm) and m is the maximum bending stress? But m is not given is it? Do I have to transpose the formula to find m?

the bending stress formula is one of the most useful equations for beams, so it should be thoroughly understood. The max bending stress is a function of the max bending moment (M) in the beam. You should read up on it more and resubmit your thoughts and attempt.