I have been talking to some structural engineers trying to find one to design foundations for my contemplated bespoke building based on hi-cube 40-ft shipping containers. The initial concept is just two containers on concrete slab with garage space between them:
Ultimately, I would like to build extra levels on top of the containers. But at this point I do not want to design that. For now I just want what is on the picture, albeit with foundations strong enough to carry the extra load of say 2 additional levels.
I have been trying to explain the above to structural engineers, specifically mentioning that any extra levels will not be directly connected to the concrete foundation but to the containers only (which would be reinforced if needed). Essentially, the containers will be the foundations for the extra levels.
But so far I have been told that they need the design of the extra levels.
Can someone please explain: why is it not sufficient to just assume extra load on the containers to calculate the concrete foundations? Why would the exact design of the extra levels make any difference (as far as the containers' concrete foundation is concerned) beyond its weight?