Quantifying the effect of beating inferred from recorded responses of tall buildings

The beating phenomenon observed in recorded earthquake responses of a tall building in Japan and of two others buildings in the U.S. are examined in this paper. The objective of the paper is to discuss the significance of beating and to estimate what percentage of total shaking energy impacting a building is contributed by beating when it occurs. Beating is prominent in the prolonged resonant responses of lightly damped structures and is a periodic vibrational behavior caused by distinctive coupling between translational and torsional modes that typically have close frequencies. Resonances from site effects may also enhance beating. Spectral analyses and system identification techniques are used herein to quantify the periods and amplitudes of the beating from strong-motion recordings of the three buildings. Quantification of beating is a first step towards determining remedial actions to improve building resilience to this phenomenon. It is shown by the analysis presented in this paper that the ratio of additional vibrational energy of a building exhibiting beating with respect to a postulated zero beating status can be as much as 105% depending on the building and the strong shaking record. Hence, beating should be considered during design and analyses process. Alternatively, remedies maybe implemented for existing buildings.