Hybrid fiber reinforced concrete-encased steel truss beams for earthquake -resistant framed structures.

The research work presented herein focuses on the behavior of a new type of precast framed structure that consists of steel-concrete hybrid beams and reinforced concrete (RC) columns for use in regions of high seismicity. The hybrid beams consist of a steel truss encased in steel Fiber Reinforced Concrete (FRC). The FRC-encased truss provides excellent strength, stiffness and energy dissipation capacity while the randomly oriented steel fibers enhance material ductility and beam shear strength. A new connection scheme was developed for adequate moment and shear transfer between the hybrid beam and RC column during large displacement reversals. Moment transfer was achieved through a combination of external steel rods and steel members connected to the truss chords, while adequate shear transfer was ensured through a bolted connection between the precast column and the embedded steel truss. In the experimental phase of this research, four beam-column connection subassemblies were tested under large displacement reversals in order to evaluate the seismic performance of the proposed hybrid beam-RC column connection. Test results showed that the proposed connection scheme was effective in transferring moment and shear during large displacement reversals. In addition, beam inelastic rotations of up to 4.4% were measured in the hybrid beams, with good stiffness retention and energy dissipation capacity. In the analytical phase of the study, models for predicting the envelope momentrotation response of the FRC-encased steel truss beams and their hysteretic behavior were first developed. Then, a prototype precast frame with FRC-encased steel truss beams and RC columns was designed for target roof drifts of 2.0% and 3.0% under ground motions with 10% and 2% probability of exceedance in 50 years, respectively, through the use of an energy-based method. The seismic behavior of the precast frame was evaluated through push-over analysis, as well as inelastic dynamic analyses under ground motions of various intensities. Analysis results showed that the proposed precast frame system is capable of satisfying the target performance criteria provided that the external connections are designed such that joint elastic rotations are limited to 0.5%.PhDApplied SciencesCivil engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/124773/2/3163784.pd