I agree, too. Also that beams are generally referred to in smaller structures.
A steel girder might hold up a bridge or be used in the construction of an office building, but a beam (generally of wood, but not necessarily) would usually be found supporting the roof of a house or apartment.
PS: The link I provided isn't working. You could try googling "beam structure wikipedia." This entry has diagrams as well and there is a link to the same entry in French, "poutre" which may be helpful in determining if this is the appropriate term for your context.
That sounds like something for a large structure, and then I might use "girder." There ARE such things as concrete girders. It really depends on scale, as a girder is really just a large beam.
This is from wikipedia.com, defining a "concrete girder":
A girder is a support beam used in construction. Girders often have an I beam cross section for strength, but may also have a box shape, Z shape or other forms. Girder is the term used to denote the main horizontal support of a structure which supports smaller beams. A girder is commonly used many times in the building of bridges, and planes.
The difference in the vocabulary words can be very subtle, so you might want to do a Google search for beam and girder, maybe look at some images online, to see if you find something that resembles your particular beam -- or girder...