Beam deflection (area moments)

[thebest99]

just started looking at area moments.

question i am stuck on is below.

use the area-moments to calculate the mid span deflection produced by the given loadings, showing clearly all steps in the method and calculation:

support condition: simply supported
span: 7.20m
section: 406x140x39 kg/m UB
material: mild steel
loading: 24 kN/m UDL

believe i have to find delflection for the beam first, then i can calc the mid span deflection. WL cubed/ E I

so first need to find the stifness of the beam , can look on net to get a figure for mild steel.
i have found one at 210kN/mm squared.

so would i have 24kN x 7.20m / 210 x 406x140x39 kg/m UB

im just confused on putting all the figures togther.

if somone could help.

 

[pongo38]

Your question is also confusing us. In particular I am confused by your statement "believe i have to find delflection for the beam first, then i can calc the mid span deflection. WL cubed/ E I". What is the difference between those two steps?

I think the value you found on the net of 210 is probably the value of Young's modulus E. If you can also find the value of I, the second moment of area (sometimes mistakenly identified as 'moment of inertia'), and you multiply that value by E, then you will have obtained a value for EI, which some people call the 'flexural rigidity'. You will need this value of EI when you use the area moment method. You have to be careful of units, because the value of I in tables is often in cm^4.

I'm looking at your statement "so would i have 24kN x 7.20m / 210 x 406x140x39 kg/m UB" and am wondering if you understand the designation of a UB such as "406x140x39 kg/m UB"? Do you know what those numbers mean?
More generally, to use the moment area method, you need to be able to draw the bending moment diagram for the case you are considering. Can you do that? I will stop there awaiting a response, because the apparent gaps in your understanding can't be dealt with all in one response.