Stub girders evolved from a need to provide an economical and volume-saving floor system within the building envelope. Traditional beam-and-girder systems tended to require a top-of-slab to underside-of-ceiling depth which, when combined with the heights of the HVAC ductwork, added significantly to the floor-to-floor height in steel-framed buildings. Integrating the electrical and mechanical service ducts into the floor framing volume through a system of short steel shapes attached to a column-to-column bottom chord eliminated the need for pass-through holes in girders and beams. The combination of the chord, the short shape segments and their attachment to the concrete floor slab by shear connectors provided an efficient composite girder that simultaneously reduced the floor-to-floor height. This became what is now known as the stub girder floor system. Making extensive use of simple shop fabrication techniques, basic elements with limited fabrication needs, simple chord-to-column connections and composite action between the floor slab and the steel load-carrying members, a floor system of significant strength, stiffness and ductility was devised. Simultaneously, this led to a reduction in the amount of structural steel that traditionally had been needed for the floor framing. Combined with continuous, composite transverse floor beams and a shortened frame erection time, this resulted in attractive cost savings. The paper describes the various system components, a simple preliminary design procedure, a practical girder analysis approach, and the detailed strength and stiffness considerations that must be used for the design of stub girders.
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