Effects Of Ground Motion Characteristics On Dynamic Response Of Bridge Pile Foundations In Liquefiable Soils

The post-earthquake investigation indicated that site liquefaction under earthquake caused serious damage to the pile-supported bridge. The seismic response of soil-pile-superstructure system in liquefying ground has been paid more attention. However, most research was focused on dynamic pile-soil interaction and parameter analysis. The effect of ground motion characteristics was few. For that purpose, on the basis of a validated numerical model of centrifuge test, comparisons between the near-fault pulse-like and near-fault nonpulse-like ground motions on the influence of the dynamic response of soil, pile foundation and superstructure were evaluated. Furthermore, the correlation of the parameters of ground motions with each response was discussed. The content and results are as follow.Firstly, numerical modeling of centrifuge test was conducted and ground motions were resonablely selected. According to the centrifuge test of pile foundation(i.e., single pile and pile group) in liquefiable soils, a three dimensional finite element model of soil-pile-superstructure dynamic system was assessed with the aid of Open Sees. Linear elastic beam-column element was employed to simulate the pile and plastic multi-yield surface constitutive model was employed to describe the dynamic properties of saturated sand. In addition, the rigid link with zero length element modeled the soil-pile interaction. The numerical model was verified through three aspects that the results of dynamic response of soil, pile foundation and superstructure. 72 near-fault pulse-like and 72 near-fault nonpulse-like ground motions are selected. Moreover, the pulse period(Tp-pulse), PGV/PGA, mean period(T_m), Arias intensity(AI), and significant duration(D5-95) of an earthquake was also used to show the charateristics of ground motions.Secondly, the effcct of earthquakeground motion charateristics on seismic response of bridge single pile was studied. On the basis of the verified numerical model of soil-single pile-superstructure system and selected ground motions, the dynamic response of soil, pile foundation and superstructure under near-fault pulse-like and near-fault nonpulse-like ground motions were compared. The correlation of the parameters of ground motions with each response was investigated. A few important findings from this representative study were summarized below. Liquefaction occurred in the upper layer of loose sand, while the lower dense sand didn’t liquefy. The average value of each response(ground surface acceleration amplification factor, pile displacement and bending moment amplitude, superstructure acceleration amplification factor, and superstructure displacement amplitude) under near-fault pulse-like ground motions was lager than that under near-fault nonpulse-like ground motions The PGV/PGA and T_m were both in good correlation with each response, and can represent the damage ability of ground motion on the soil- single pile-superstructure system. The upper limit and lower limit between each response and PGV/PGA, T_m were assessed with the aid of the 95% prediction interval.Finally, the effcct of earthquake charateristics on the seismic response of bridge pile group was discussed. On the basis of the verified numerical model of soil- pile group-superstructure system and selected ground motions, the dynamic response of soil, pile foundation and superstructure under near-fault pulse-like and near-fault nonpulse-like ground motions were compared. Furthermore, the correlation of the parameters of ground motions with each response was investigated. It should be mentioned that the dynamic performance of ground was not studied. A few important findings were summarized below. The average value of each response(pile1 displacement and bending moment amplitude, superstructure acceleration amplification factor, and superstructure displacement amplitude) under near-fault pulse-like ground motions are lager than that under near-fault nonpulse-like ground motions. The PGV/PGA and T_m were both in good correlation with each response, and can represent the damage ability of ground motion on the soil-pile group-superstructure system. The upper limit and lower limit between each response and PGV/PGA, T_m were assessed with the aid of the 95% prediction interval. The difference in seismic response between single pile and pile group system was assessed. Generally, the bending moment and superstructure displacement amplitude of single pile system were both lager than in pile group system under near-fault pulse-like and near-fault nonpulse-like ground motions. The superstructure acceleration amplification factor of pile group system was lager than in single pile system.