## 1 Introduction  
In recent years, seismic activities have sharply increased around the world [1]. The increase in the strength and number of seismic activities requires predicting the seismic performance of structures to ensure their stability during earthquakes [2; 3; 4]. The seismic performance of a structure depends on the characteristics of ground motion and the structural elements of the structure. Single-degree-of-freedom (SDOF) structures have a relatively small number of factors to account for in the response of the structures in an earthquake [5]. On the other hand, the seismic response of multi-degree-of-freedom (MDOF) structures, which are composed of various structural elements, cannot be easily evaluated. This is because MDOF structures are not dominated by a specific factor in seismic analysis [6; 7]. Furthermore, the nonlinear behavior of materials and components, which would occur under an earthquake load, makes predicting the seismic response of MDOF structures more difficult [8]. The seismic response of a structure is also affected by the characteristics of ground motion [9; 10]. Therefore, for bridges composed of various structural components, such as piers, bearings, and girders, this study examined the effects of ground motion and aspect ratio on the seismic performance of a bridge structure. Ground motions can be divided into near-fault and far-fault ground motions, depending on the distance from the epicenter and the characteristics of each ground motion. Recent studies have analyzed the effects of near-fault ground motion on architectural and civil structures, such as nuclear power plants, dams, bridges, and buildings [11; 12; 13; 14]. Near-fault ground motion generally shows strong and narrow-band pulses for a short period in spectral accelerations [15; 16; 17]. Therefore, structures with a short period of vibration are mostly affected by near-fault ground motion [18; 19]. On the other hand, far-fault ground motion, which has long-period characteristics and relatively small response pulses as it travels over long distances, influences structures with a long natural period [20; 21]. Therefore, this study evaluated the effects of near-fault and far-fault ground motions on the seismic performance of bridge structures. In particular, near-fault ground motions were selected to have the characteristics of forward directivity and fling step. A total of 14 ground motions were involved in the study (i.e., seven seismic waves for each ground motion based on recent ground activities). In addition to seismic ground motions, the seismic behavior of bridge structures is significantly affected by the height of the bridge [22]. That is, the bridge column is one of the most vulnerable parts of a bridge when subjected to ground motion, which requires accurate modeling and seismic analysis [23]. The height of a pier can be defined as the aspect ratio of the pier, which is the ratio of the length of the pier to the diameter of the cross section. In the design process of a bridge, shear and flexural failures are strongly dependent on the aspect ratio of the pier. In general, as the aspect ratio increases, the failure of a bridge changes from shear to bending mode. The seismic performance of the entire bridge can also be affected by the aspect ratio of the pier [24]. Some recent studies [25; 26] analyzed the effect of the aspect ratio of a pier on the seismic response of a bridge and showed that the displacement and shear force of the pier increased with an increasing aspect ratio but decreased after a certain aspect ratio. Studies on seismic response with respect to aspect ratio in a bridge system are still limited. Therefore, various aspect ratios of piers were considered to investigate the seismic behavior of a structural bridge system under near-fault and far-fault ground motions. The bridge considered in the study is a prestressed concrete (PSC) I-type bridge. Numerical modeling was performed using detailed drawings of a real bridge.