Behavior of fiber-reinforced concrete-encased open web steel joist composite members under monotonic and reversed cyclic loading

Frequent earthquakes in recent years throughout the world have prompted the structural engineering community to pursue considerable research on the behavior of structures under seismic loading. One major thrust in research is to improve design of conventional reinforced concrete (RC) and steel structures for better performance under strong seismic shaking. Another potential area of research, as many structural engineers feel, is to develop economic and innovative structural systems with improved seismic performance. One such new and innovative structural system is a fiber reinforced concrete-encased open web steel joist composite frame.; There are many advantages of the proposed system. As per current practice, reinforced concrete (RC) structures need considerable confinement and stirrups in plastic hinge regions and joints for seismic resistance. This often causes congestion, making it difficult to properly place the reinforcing steel and concrete. More importantly, all this work is quite labor intensive, and therefore may not be cost effective in an era of high labor costs and possible labor shortages. The proposed composite system completely eliminates the above problems. All the connections in the system are steel-to-steel. Therefore, the system can be used with cast-in-place or precast construction. Besides, design and detailing of the joints is significantly simplified.; To study the behavior of this new structural system, a comprehensive experimental and analytical program was undertaken. Six composite beam specimens and one frame (all half-scale) were tested under reversed cyclic loading. The test results are very encouraging. The two materials (structural steel and FRC) 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. In addition, ten beam specimens were tested under monotonic loading. The flexural capacity, shear strength and hysteretic response of the structural members can be quite accurately predicted by the proposed analytical models for design and analysis purposes. It is strongly felt that this type of innovative composite system is very promising for seismic as well as non-seismic load applications.