What is the aproximate load capacity of an 8" I beam over a 20' span.
You haven’t included enough info for me to help you get the answerm but hopefully these two links will enable you to figure it out..
You’ll need to visit two sites. This one for the beam properties:
http://efunda.com/math/areas/IbeamIndex.cfm
And this one for a calculator:
http://efunda.com/formulae/solid_mechanics/beams/casestudy_bc_simple.cfm
Hope this helps.