Doctor of Philosophy

dissertationThis research investigates the effect of using a combination of high strength concrete (HSC), high strength steel (HSS), and steel fibers on the seismic performance of moment resisting frames (MRFs). In the first part of the study, reinforced concrete components were tested in the laboratory under monotonic and cyclic loading conditions to obtain their nonlinear characteristics, such as strength, stiffness, and hysteretic behavior. Based on these test results, numerical simulations were performed using deteriorating hysteretic models that account for strength and stiffness deterioration to identify the nonlinear modeling parameters for the different components. These parameters were then used to assess the seismic performance of single- and multi-degree-of-freedom (SDOF and MDOF) systems. The methodology outlined in FEMA P695 report was used to assess the performance of the different systems using median collapse capacity in terms of spectral acceleration. Nonlinear static and dynamic analyses were performed to analyze the overall behavior of the structures, from their elastic response until the global collapse limit state is reached. The specimens with HSC and conventional steel exhibited similar ductility to normal strength concrete (NSC) components. The use of HSS increased the components strength, but reduced their ductility and spread of plasticity. Steel fibers were used in combination with HSC to create high strength fiber reinforced concrete (HSFRC) specimens, which achieved larger elastic stiffness and slightly higher flexural capacity compared to similar specimens without steel fibers. However, their cyclic deterioration rate was not largely increased. The numerical models showed that the larger strength of HSC and HSS in SDOF systems can overcome the reduction in ductility in these components. This is partially due to the fact that HSC components exhibit elastic behavior under large seismic demands, which reduces their susceptibility to early collapse due to P-? effects. From the MDOF analysis using 12- and 20-story MRFs, similar conclusions were drawn for the seismic performance of the 12-story building. However, the more ductile components led to the highest collapse capacity in the 20-story building due to varying column cross sections across different stories and nonuniform distribution of the nonlinear modeling parameters which affected the HSFRC components significantly