Steady-State Versus Run-Down Tests of Structures

Steady-state and run-down vibration tests have been made on two modern multistory buildings. The response curves from the tests have been analyzed and the results compared. Damping determined from a run-down test is up to 2.5 times as large as the damping determined from a steady-state test. Accurate speed control is needed to precisely define the resonance curve from a steady-state test. It is concluded that the data from past forced vibration tests must be treated with caution. For various levels of excitation the damping in the lowest translational mode was found to vary between 0.5% and 1.0% for a steel frame structure and between 1.0% and 2.0% for a reinforced concrete building. These values of damping are considerably lower than values usually cited in the literature.