Structural Engineering Problem

Hey guys, just a quick problem which Im getting a bit confused with.
I need to choose an appropriate sized I Beam for a structure,
I already know the loading on the beam (UDL=28 KN/m) and the length is 2.5m.
Can someone explain the procedure of selecting the correct steel I Beam using the limiting deflection equation with L/360?

Thank You

Reply 1

thefish_uk

Original post by j2345

I am going to assume you have two things:
1.) the deflection equation you need (memory tells me it is 5WL^3/384EI in this case... correct me if I'm wrong!)
2.) a databook with suitable geometric properties of various sections (e.g. from the "blue book")

In which case you can work out your maximum permissible deflection = 2.5/360 = 0.007m.

You then set deflection in the above equation to this (0.007 = 5WL^3/384EI) and solve to find the minimum value of I... you know W = 28000, L = 2.5 and E = 205*10^9. Why is it the minimum? Because looking at the equation, a beam of lower I would deflect more than this.

When you have this minimum value of I, you look in your data book of section properties to find an I-beam with Ixx slightly bigger than this.