Seismic fragility analysis of clay-pile-pier systems considering the optimization of ground motion intensity measures

The performance of clay-pile-pier system under earthquake shaking was comprehensively examined via threedimensional finite element analyses, in which the complex stress-strain relationships of a clay and piled pier system were depicted by a hyperbolic-hysteretic and an equivalent elastoplastic model, respectively. One hundred twenty ground motions with varying peak accelerations were considered, along with the variations in bridge superstructure mass and pile flexural rigidity. Comprehensive comparison studies suggested that peak pile-cap acceleration and peak pile-cap velocity are the optimal ground motion intensity measures for seismic responses of the pier and the pile, respectively. Furthermore, based on two optimal ground motion intensity measures and using curvature ductility to quantify different damage states, seismic fragility analyses were performed. The pier generally had no evident damage except when the bridge girder mass was equal to 960 t, which seemed to be comparatively insensitive to the varying pile flexural rigidity. In comparison, the pile was found to be more vulnerable to seismic damage and its failure probabilities tended to clearly reduce with the increment of pile flexural rigidity, while the influence of the bridge girder mass was relatively minor.