An architect may come up with a building design, but it's the Structural Engineer's responsibility to fit the structure to the architecture, and decide on what structural system is best suited to that particular building. The Structural Engineer may design the beams, the columns, the walls, the foundation or any structural element to make the building stand up.
A Structural Engineer might also be involved in the demolition or dismantling of a structure, either permanently or in order to repair it. For both of these processes, they need to know about the forces that act on a structure from the stresses put on a bridge by heavy traffic or by strong winds on a tall building or on any structure by seasonal temperature changes.
Structural Engineers also inspect and report on structural building buildings and may prepare designs and details for repair and remedial works. Such defects may range from serious problems such as subsidence or collapse to minor defects such as wall tie corrosion or roof spread.