FRC-encased steel joist composite reams under reversed cyclic loading

Experimental and analytical studies were conducted to investigate the behavior of fiber reinforced concrete-encased steel joist composite members subjected to reversed cyclic bending. This new and innovative structural system completely eliminates the need for any shear connectors between the steel joists and surrounding concrete as well as the need for conventional longitudinal and transverse reinforcement, all of which are quite labor intensive. All connections in the system are steel-to-steel; therefore, the system can be used with cast-in-place or precast construction. Five one-half-scale specimens were tested, each consisting of open web steel sections encased in concrete containing discrete steel fibers. In the test program, the most important parameter studied was the configuration of steel elements. The test results are very encouraging. The two materials (structural steel and fiber-reinforced concrete) interact to provide stable hysteretic behavior with excellent energy dissipation and ductility. The study indicates that the presence of steel joists as well as steel fibers can adequately inhibit the chances of brittle shear failure, thus making the system very suitable for seismic resistant structures. The specimen load-carrying capacity and its hysteretic response can be quite accurately predicted by the proposed analytical models.