Method for examining structures having high natural vibration frequency using alternating manual vibration-exciting method

Abstract

Disclosed is an alternating human vibration-exciting method for obtaining a free vibration waveform of buildings or civil structures having a natural vibration frequency more than 2.5 Hz. First and second same-number sets of subjects having similar weights alternately apply exciting forces to a wall on a top of the structure. An electronic beat-sound generator is adjusted to a two-beat mode to generate two alternating beat sounds repeatedly so that the first and second sets can apply vibration exciting forces repeatedly at a frequency of half of the natural vibration frequency of the structure obtained by micro-tremor measurement, while alternately synchronizing their actions to the two alternating beat sounds, respectively. The vibration exciting action is stopped after the structure is brought to a sufficient resonance state, thereby obtaining a free vibration waveform having an amplitude several tens of times larger than that of the micro-tremor of the structure having a natural vibration frequency more than 2.5 Hz, at which frequency it is generally difficult to perform a human vibration excitation. The free vibration waveform is used for calculating the damping ratio or natural vibration frequency.

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