Maximum stress in beams with different cross sections

[shaw600]

Homework Statement

Here is the problem:

I have to calculate the maximum stress for A, B and C.

Homework Equations

I used:

σ = y*F*L / 4*I (but I don't think this is right)

σ = maximum stress
y = Perpendicular distance from to neutral axis
F = load
L = length of beam
I = moment of Inertia

The Attempt at a Solution

Using:
σ = y*F*L / 4*I

I got the following:
A = 1.241
B = 5.562
C = 4.085

 

[SteamKing]

Your problem statement is not clear. Is stress bending stress? Is it shear stress? Is it combined stress?

In any event, your formula for stress is suspect. First, you should draw a free body diagram of your beam with the applied loads. Construct the shear and bending moment curves from that.

 

[cmmcnamara]

Yea you need to be a bit more specific with the problem statement. Although I assume your problem is for maximum bending stress. In that case your equation is suspect still. Your maximum bending stress will occur where the bending moment is maximum and the selected point is the maximum distance from the beam's neutral axis. So to even consider your problem you'll need to derive the bending moment function first and find the point at which it is maximum, then compute the neutral axis location on each cross section and find the maximum distance from each.