Rate-dependence in high performance fiber-reinforced cementitious composites for seismic retrofits

This research focuses on the continuing development of a retrofit strategy for steel framed structures that can not only accommodate floor plans and secondary system layouts of the existing facility, but also possibly provide minimal disturbance to the function of the building during installation. The retrofit strategy consists of a series of precast infill panels within the frame that act as deep beams under lateral load. The panels are composed of a high performance, fiber-reinforced cementitious composite (HPFRCC) that does not spall, strain hardens in tension, and exhibits fine multiple cracking, leading to energy dissipation under cyclic loading.; Of particular interest in this work is the response of a steel frame structure to an earthquake with the retrofit system in place. Simulating the system response requires a reliable model for the infill panels, which in turn requires a thorough understanding of the rate-dependence of the HPFRCC materials. This research focuses on determining the rate-dependence of HPFRCC materials under tension, compression, and cyclic loading conditions. The research objectives are: (1) Determine the rate-dependence of selected HPFRCC materials in monotonic tension, monotonic compression, and cyclic loading up to seismic-level strain rates. (2) Develop a reliable model for the hysteretic behavior of the infill panels. (3) Simulate the response of a structure to a series of earthquakes with the retrofit system in place.; It was found that the strength, stiffness, and tensile strain capacity of the selected HPFRCC materials were significantly affected by increasing strain rate. This in turn was found to have an important influence on the lateral load capacity, drift at which softening occurred, and post-peak softening slope of the infill panels. The retrofit system was shown to decrease beam-column joint rotations, the probability of beam-column connection failure associated with these rotations, and roof and interstory drifts by up to 50%, making it a viable solution for retrofitting steel frame buildings and critical facilities.