Energy and directionality characteristics of seismic sequences and typical bridge response in the Ms6.4 Yangbi earthquake of May 21, 2021

In this paper, the energy and directionality characteristics of the ground motion sequence are investigated for the 2021 M6.4 Yangbi earthquake. Firstly, this paper proposes the omni-directional input energy spectrum to analyze the seismic characteristics, which effectively illustrates the input energy of the single degree of freedom system across all directions and periods, thereby comprehensively presenting the bidirectional characteristics of earthquakes from the perspective of the input energy. Then numerical simulations of a typical bridge in Yangbi earthquake were conducted to analyze the cumulative effect of seismic sequence and the influence of seismic directionality on bridge damage. The Park-Ang damage index was employed to quantify the bridge damage. The results show omni-directional input energy spectrum and damage indices of bridges under the seismic sequences were greater than those under the mainshock alone, indicating that the seismic sequence can exacerbate the structural damage caused by the mainshock. The foreshocks and aftershocks altered the overall seismic directionality and frequency spectrum characteristics of the seismic sequence. The predominant orientation of the omni-directional input energy spectrum reflects the directional characteristics of the ground motions, and seismic directionality significantly impacts the bridge structure. In the case study, the bridge damage was more severe when the bridge axis was parallel to the predominant orientation than under the original bridge condition. Data availability: Data will be made available on request.