Seismic fragility analysis of building clusters considering the effects of mainshock-aftershock sequences

The impact of the mainshock earthquake on the regional building cluster is significant, directly causing varying degrees of damage to many houses. A large amount of onsite seismic loss observation data indicate that aftershocks after the main earthquake also impact the damage to and vulnerability of regional buildings. To study the seismic fragility and risk of typical building clusters under mainshock-aftershock sequences, this paper innovatively proposes a structural seismic fragility model that considers the intensity measures of the mainshock-aftershock by combining total probability and Bayesian theory. A computational intensity model has been developed that considers the directionality of ground motion under mainshock-aftershock sequences. The established model was verified and analyzed on the basis of 384,882 accelerations monitored by nine strong motion stations during the Jiuzhaigou earthquake on August 8, 2017, in China. The calculated intensity point cloud and stripe models were generated on the basis of the directional effect of ground motion. Using the Chinese earthquake intensity scale and the proposed computational intensity model, the fragility of three types of building clusters (1212 buildings) affected by the Jiuzhaigou earthquake was estimated, and a structural failure probability model considering mainshock-aftershock sequences was established. A seismic fragility curve of a building cluster considering the influence of mainshock-aftershock sequences was plotted via the Gaussian process, least squares regression algorithm, and data-driven techniques. An innovative structural fragility correlation surface was generated to analyze the correlation characteristics between different fragility levels under the influence of mainshock-aftershock sequences. The traditional earthquake damage index method has been improved, and a structural fragility index function considering the impact of mainshock-aftershocks has been proposed.