Questions and discussion for this lecture live here. Fire away by hitting Reply below 
Hi, do these equations still apply to a box girder section? What would the stresses look like for this type of shape? Thank you 
Hey @graving,
In theory, you can still apply the same principles to the analysis of a box section like this. But you can’t do it blindly, you need to make sensible modifications to account for the fact that you have a tapered section and there’s a giant hole in the middle of it!
If I was looking for a first approximation, I would probably start by treating this as two T-beams, sharing the load. This will almost certainly underestimate the capacity of the section but will give you an idea of the approximate capacity of the section.
Hope that helps.
Seán