What type of steel structure usually features smaller beams framed into large members that span between supports?

A beam-and-girder system is typically employed in steel structures where smaller beams (also known as secondary beams) are framed into larger primary members known as girders. The girders span the distance between supports and carry the load from the smaller beams that distribute the load from the building's floors or roof. This system allows for larger open spaces within buildings because the girders can cover greater distances without needing support from below, facilitating flexible interior layouts.

In contrast, other options describe different structural systems. A trussed wood joist would use a system of intersecting wood members, which isn't relevant to steel structures. A flat slab refers to a reinforced concrete structure without beams, relying instead on slabs supported directly by columns. Lastly, an open-web steel joist system utilizes lighter members that form a web-like structure, typically used in places where large spans are needed, but it doesn’t primarily consist of large girders as in a beam-and-girder system. Each of these alternative structural forms serves different purposes and design criteria, highlighting the unique characteristics of the beam-and-girder system in steel construction.