A box girder or tubular girder is a girder that forms an enclosed tube with multiple walls, as opposed to an I- or H-beam. Originally constructed of wrought iron joined by riveting, they are now made of rolled or welded steel, aluminium extrusions or prestressed concrete.
The old Britannia Bridge with train track inside the box-girder tunnel.
Section of the original tubular Britannia Bridge
The patent curved and tapered box girder jib of a Fairbairn steam crane
Bridge built using multiple box girders
An I-beam is any of various structural members with an I or H-shaped cross-section. Technical terms for similar items include H-beam, universal column (UC), w-beam, universal beam (UB), rolled steel joist (RSJ), or double-T. I-beams are typically made of structural steel and serve a wide variety of construction uses.
An I-beam used to support the first floor of a house
Mark di Suvero's Victor's Lament (foreground in red) on the campus of Muhlenberg College in Allentown, Pennsylvania, is an I-beam sculpture paying tribute to the rich history of steelmaking in the Lehigh Valley region of the eastern Pennsylvania.
A rusty riveted steel I-beam