i think i wasnt that clear about my design - so i sketched something to explain it alittle better (in the meantime im working on somthing more detailed)

any way i will not be using no i beams or H sections but regular rectangular hollow section steel tubes dimentions of 100*50*3.2 and 40*40*1.5

for the epoxy method i have seen some builders use that method - but are there any other methods?