Recent earthquakes around the world have demonstrated that steel moment-frame buildings designed based on older seismic provisions are seismically deficient. To enhance the seismic performance of these buildings, a new seismic retrofit system has been developed and evaluated experimentally as part of a two-story steel moment-resisting frame, designed in California in the 1980s. The proposed retrofit system consists of high-performance fiber-reinforced concrete (HPFRC) infill panels acting as energy dissipation elements that can be easily replaced after a major earthquake. Through two large-scale hybrid simulation tests of the retrofitted two-story steel moment-resisting frame, it is demonstrated that (1) the proposed retrofit system is effective in terms of reducing the maximum story drift ratios and residual deformations of the retrofitted steel moment resisting frame relative to the predicted bare frame performance, and (2) the structural damage of the retrofitted steel moment-resisting frame is kept minimal because energy dissipation is concentrated in the infill panel retrofit system. © 2013 American Society of Civil Engineers.