A new endurance time analysis method for damage evaluation of high arch dams under the oblique incidence of mainshock-aftershock seismic sequences by wavelet decomposition

Abstract

Pulse and oblique incidence features that may be generated by near-fault seismic sequences are neglected in current earthquake-resistant design codes for arch dams. To solve the shortcomings of endurance time analysis method which cannot consider near-fault pulse-like ground motions, this paper attempted to develop a new endurance time analysis method by wavelet decomposition to assess the differences in damage mechanisms of arch dams under the cross-stream and stream oblique incidences of near-fault seismic sequences. This study decomposed a typical near-fault earthquake into high-frequency and low-frequency ground motion through wavelet decomposition, which is used to perform several nonlinear dynamic analyses under different seismic intensities and seismic sequence incidence angles. On the basis of dynamic calculations, the local and global damage indices of the dam were presented, with a focus on the comparison of the damage distribution and damage volume ratios of arch dams under the action of single and sequence earthquakes and by analysing the damage mechanisms of arch dams under two diagonal incidence conditions at different peak accelerations. Then, the effects of different frequency components of ground motions on dam damage indices were compared, and finally, additional damage to the dam after the mainshock damage was quantified for various aftershocks. The proposed novel prediction model was used to estimate aftershock damage by considering mainshock damage. The numerical results indicate that the dam damage development is highly complex during original mainshock cross-stream and stream oblique incidences. This finding differs from dam damage that spread from the downstream face to the upstream face during the vertical incidence. The dam damage degree is smaller for the original mainshock stream oblique incidence than for the original mainshock cross-stream oblique incidence. The original aftershock induces stronger damage requirements on the damaged dam during the mainshock than during the high-frequency aftershock. Original and high-frequency seismic sequences with cross-stream and stream oblique incidences do not contribute to variations in dam damage patterns during aftershocks. Therefore, the influence of near-fault pulse impacts and the oblique incidence angle of seismic sequences need to be considered comprehensively in the seismic calculations and reinforcement studies of arch dams.