91-0016 Closed-Loop Modal Testing of a 27-Story Reinforced Concrete Flat Plate-Core Building H.R. Somaprasad, T.Toksoy, H.Yoshiyuki, A.E.Aktan 1991 University of Cincinnati 156 PB92-129980 15 Modal testing of a 27-story reinforced concrete flat plate building with concrete cores was performed to identify a reliable analytical model. Closed-loop modal tests were performed to acquire data by utilizing a linear inertia-mass exciter capable of generating a higher level of force to overcome wind excitation. Furthermore, the level of force permitted the observation of rocking. Recently developed HP SINE signal processing software with HP-3565S measurement hardware was utilized in a closed-loop test setup to control the excitation and to acquire and process the data. The natural frequencies, damping, and modal vectors were determined by post processing the measured data. It was possible to determine the mass-orthonormal modal vectors and flexibility without assuming a mass matrix. The rotational flexibility of the core foundation due to rocking was also quantified. A comparison of the current and previous model test results is presented. An increase in the level of excitation force resulted in variations in the dynamic characteristics and lateral flexibility of the building. The performance of the hardware and software and the difficulties encountered during the test are detailed in this report. Critical parameters governing the data acquisition, signal processing, and excitation generation, which may have implications on structural control applications, are discussed. Full Scale Tests, Reinforced Concrete Buildings, Structural Identification, Closed Loop Modal Tests, Field Investigations, Damping, Multistory Buildings, Flat Plate-Core Buildings, and Natural Frequencies.