This thesis covers the investigation of active damping on a cruciform beam laboratory structure along with the development of this structure. Also important to this and other research was the development of a calibration apparatus that produces accurate, repeatable calibrations for several types of laboratory instruments. The cruciform beam model is developed out of a simpler beam-cable model with the addition of a crosspiece that produces a pair of closely-spaced modes. This model is developed theoretically and verified experimentally. Experimental verification is also obtained for theoretical results in the simultaneous design of a structure and control system. A spatial filtering method for determining the modal response of the structure from the physical response is also investigated.