I'm writing from Bangladesh, in my country people constructed their building using two types of concrete at the same structure. They casted column with normal weight concrete (using stone chips fc' = 4000 psi) and beams & slab with light weight concrete (using brick chips fc' = 2500 psi)to minimize construction cost. My question is, what about the beam-column joint strngth.If the beam-column joint acts as a part of the column, then can it servibe or not as it is casted with a concrete with fc' = 2500 psi but the column was designed with a load capacity fc' = 4000 psi.

You can use reinforced concrete calculator at
http://civilengineer.webinfolist.co...alysis.htm