## 1 Introduction
These findings indicate that the dynamic response of bridge piers is significantly greater under multidimensional ground motion loading than under single-directional earthquake excitation, emphasizing the importance of pondering multidimensional ground motion effects in bridge design. Pulse ground motions result in significantly higher destructive loadings than non-pulse ground motions. This increased intensity makes it particularly susceptible to structural damage and potential collapse. [PERSON] et al. [17] developed a detailed nonlinear analysis model that encompasses the full range of potential damage to components, ranging from minor damage to total failure. The causes of earthquake obliteration of bridge components and the mechanism of beam failure under near-fault earthquakes have also been studied. [PERSON] et al. [18] employed a vulnerability analysis method to evaluate the seismic resilience of tall bridge piers under near-fault motion, and reported that damage was more likely to occur when the bridge pier height was greater. [PERSON] et al. [19] studied the influence of various factors, including pier height, aspect ratio, and longitudinal reinforcement, on the behaviour of reinforced concrete bridges during earthquake events in near-fault regions. [PERSON] et al. [20] conducted shaking table tests on tall bridge piers, revealing that the speed and frequency of seismic pulses influence their vulnerability. [PERSON] et al. [21] found that near-field pulse earthquakes increase the interaction between piers and surrounding water, thereby intensifying structural risks. These studies underscore the critical need for advanced modelling and design strategies to mitigate the influences of near-fault seismic motions on bridge integrity. At present, there are few studies on the damping ratio of tall bridge pier structures. Generally, only the dynamic response under a fixed damping ratio is concerned, and the damping is often limited to isolated parameters, ignoring the influence of high-order modes and low-order modes. There are few studies on pulse ground motion, which are often only analysed by unidirectional horizontal pulse input, ignoring the phase modulation effect of multidimensional input. Therefore, the earthquake features of tall bridge pier structures' combination of damping variation and synthetic multidirectional pulse input have yet to be investigated. Accordingly, this study employs ground motion synthesis software to generate varying pulse ground motions and non-pulse ground motions with characteristic periods (T\({}_{\text{g}}\) = 0.45 s; T\({}_{\text{g}}\) = 0.40 s; T\({}_{\text{g}}\) = 0.35 s) for analysis. For the first time, the differential effects of various damping ratios on the displacement and shear stress responses of tall bridge pier structures under different dimensions of pulse and non-pulse ground motions are systematically analysed, and the interaction between multidimensional ground motions and structural damping is revealed. The extreme influence of pulse ground motion on a tall pier structure is clearly quantified by time history analysis. It is found that the peak values of displacement and shear stress response under pulse ground motion are significantly higher than those under non-pulse ground motion. In the long-term, the pulse effect exceeds the dominant effect of the damping ratio on the dynamic response, and the response of different sections under multidimensional ground motion is quite different. Through multidimensional pulse seismic input, variable damping ratio control and nonlinear time history analysis, this study systematically reveals the failure mechanism of tall-pier bridges in near-fault earthquakes, proposes a new idea of ground motion direction sensitivity and damping ratio optimization, and provides a theoretical basis for the follow-up study of multifield coupling of bridge pier structures.