you can have a flush or drop down concrete beam, or a steel beam enclosed in the floor, partially dropped down or fully below. matter of choice, price, architecural need, availabilty of material and installers.
if not needed as steel i-beam for span or load reasons, i prefer a formed concrete beam, integrated into the insuldeck floor. as there likely will be a concrete forming crew doing the insuldeck, its easy to form a concrete beam.
same materials and tools, a little plywood and some 2x4,s... concrete pump will do the heavy work, no crane needed to hoist anything in place. no need for special connections or imbeds, or welding etc. just rebar, as with the walls.
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