substructure
Lower portion of a building infrastructure, including everything that is constructed below the ground level. It is primarily responsible for providing a stable base and support for the superstructure are safely transmitted to the ground and that the building remains anchored and secure.
superstructure
Parts of a building or structure above the ground level that includes the structural framework and all components that contribute to the functionality and appearnace of the building. It is responsible for carrying the loads of the building's interior and exterior elements and transferring them down to the substructure.