Shear Stress in Beams - Full Working, getting wrong

[smr101]

Hi,

I'm doing question (c)(ii) in the image below, full working is provided below:

(c)(i) is 150kPa.

I = bh^3/12 - 2 * bh^3/12
(0.25 * 0.256^3)/12 - (2* (0.119 * 0.22^3)/12)
= 1.3831 x 10^-4 m^4

Q = y*A
= 0.119 * 0.018 * 0.250
= 5.355 x 10^-4 m^3

shear force = (150000 * 5.355 x 10^-4)/(1.3831 x 10^-4 * 0.25)
= 2.32 MPa

I know that the solution is shear force minimum = 48.4 MPa.

Where have I gone wrong?

Thanks!

 

[PhanthomJay]

looks like you used the wrong thickness when calculating the min shear stress in the web (you used the flange width in error)

 

[smr101]

looks like you used the wrong thickness when calculating the min shear stress in the web (you used the flange width in error)

That's it, thanks.

 

[SteamKing]

Hi,

I'm doing question (c)(ii) in the image below, full working is provided below:

(c)(i) is 150kPa.

Shear force is not measured in Pascals. It is measured in Newtons.

I = bh^3/12 - 2 * bh^3/12
(0.25 * 0.256^3)/12 - (2* (0.119 * 0.22^3)/12)
= 1.3831 x 10^-4 m^4

Q = y*A
= 0.119 * 0.018 * 0.250
= 5.355 x 10^-4 m^3

shear force = (150000 * 5.355 x 10^-4)/(1.3831 x 10^-4 * 0.25)
= 2.32 MPa

You're supposed to be calculating shear stress here.

I know that the solution is shear force minimum = 48.4 MPa.

Where have I gone wrong?

Thanks!