Structural Control ãVibration control of civil structures is more recent as compared to machines & aerospace vehicles. ãEarthquakes and wind loads - main sources of structural vibrations. ãControl vibrations by: changing rigidity, mass, damping, shape, or applying passive or active control forces. ã> 20 full scale active control appl. in Japan ãPassive base isolation used in USA. ãRetrofitting reqd. if new seismic activity detected ãHigh strength may result in high acceleration levels, so increasing strength alone wont always work. Structural control versus Mechanical & Aerospace control ãEnvironmental disturbances (wind, earthquake excitations) occur over wide range of frequency and amplitudes, i.e., they are uncertain, whereas mechanical loads are usually deterministic. ãCivil structures (without control) are stable and may get destabilized with active control, whereas aerospace structures require active control for stabilization. ãPerformance specifications for civil structures are coarse (e.g., peak amplitude, time for motion to settle down).