# Seismic Study of An Isolated Cable-Stayed Bridge under Near-Fault Ground Motions
## 1 Introduction  
Earthquake-stricken regions display a distinct pattern with strip distribution along active faults. Near-fault ground motion demonstrates specific characteristics, including short duration, high amplitude, and pronounced pulses, which markedly differ from far-fault ground motion [1; 2; 3]. Due to the proximity of the pulse period of near-fault ground motion to the natural period of structures with long periods, the amplification of the seismic response of structures is significant, which poses a substantial threat of damage. Wave passage effect [4] and soil-structure interaction (abbreviated as SSI) [5] are crucial factors affecting the seismic response of structures under the influence of near-fault ground motion. Previous seismic events have shown that insufficient width of expansion joints between adjacent structures will cause pounding of structures, leading to damage and potential collapse. For example, during the 1971 San Fernando earthquake in the United States [6], the 1995 Hanshin earthquake in Japan [7], the 2008 Wenchuan earthquake in China [8], and the 2011 Christchurch earthquake in New Zealand [9], the expansion joints of bridges were damaged due to bounding between the abutments and the girders at both ends of the segments. The excessive opening relative displacement between segments further contributed to girder unseating [10; 11]. Therefore, the AASHTO Guide Specifications for LRFD Seismic Bridge Design [12] propose constraints on the basic period ratio between two adjacent units to mitigate the risk of bounding. However, it is important to note that the AASHTO specifications mainly focus on \"conventional\" bridges. For long-span isolation bridges, there are currently few studies considering the impact of traveling waveeffects on potential poundings between adjacent segments. Consequently, when designing \"unconventional\" bridges, engineers often refer to the provisions of the AASHTO code for \"conventional\" bridges, potentially leading to designs that are not conservative enough. Cable-stayed bridges typically incorporate a \"floating system,\" characterized by the absence of a longitudinal connection between the main beam and the tower columns. This design contributes to a longer fundamental period [13]. However, when exposed to significant ground motions, the lack of longitudinal displacement limiters not only leads to large displacements in the main bridge but also intensifies bounding between the main bridge and the approach bridge, resulting in a series of catastrophic consequences [14]. In response to these challenges, substantial research efforts have been conducted to develop dynamic control devices. These devices include passive [11], semi-active [15], and active control systems [16], each specifically designed for long-span cable-stayed bridges. Friction pendulum bearings (FPBs) [17; 18] and fluid viscous dampers (FVDs) [19] are often used as passive control devices to limit the movement of cable-stayed bridges during earthquakes. FPBs stand out as a preferred choice for long-span bridges due to their independence from the superstructure's mass, excellent recentering capability, and durability. [PERSON] and [PERSON] [20] assessed the effectiveness of friction pendulum bearings (FPBs) in enhancing the seismic performance of bridges using single-degree-of-freedom and two-degree-of-freedom models. Their analysis highlighted the significant influence of concave friction coefficients on the response and provided valuable recommendations. [PERSON] et al. [21] presented a framework for the seismic analysis of the coupled high-speed train bridge with the isolation of friction pendulum bearing. On the other hand, FVDs work as a passive energy dissipation system to dissipate the vibration energy of the tower and beam. Typically installed between the main beam and the tower frame, FVDs aim to reduce the longitudinal vibration of the main beam. [PERSON] et al. [22] investigated the seismic performance of cable-stayed bridges with FVDs under random seismic excitation.