Steady state vibration tests of a six-storey reinforced concrete building

Five modes of vibration of a six-storey reinforced concrete building were excited by steady-state resonance testing. Good correlation between predicted and measured frequencies was obtained. In the lateral translation tests, two translation modes and the vibration of the roof as a free-free beam were excited. Damping measured in the fundamental mode was 4.1% critical and the average contribution of foundation compliance to the top-storey deflection was 32%. Damping in the second translation mode was 6.6% and of the free-free beam vibration, 3.6%. The first torsional mode of the building was excited, and for an eight-fold increase in excitation force, the natural frequency reduced by 1.2%, indicating a slight degree of non-linearity in the response. Damping in this mode was 6.9% , no change being noted for the eight-fold force increase. In the longitudinal direction, two modes were excited, the first torsional mode and the first longitudinal translation mode. Properties of the former were similar to those determined from the torsional response test. Damping in the translation mode was 10.1% and the foundation compliance contributed 24% of the top-storey deflection.