## 1 Introduction  
A gantry crane is a special equipment widely utilized in ports and freight stations as one of the most significant components of the modern system. It is non-negligible in cargo transportation as a lifeline of goods and materials during and after a natural hazard especially the post-earthquake reconstruction. In recent years, there has been an increasing tendency in structure design to consider seismic safety and appreciate the estimation of the seismic performance of a structure, especially large infrastructure. Compared to traditional steel moment frames, the gantry crane has a larger span, bigger payload, and more complicated operating conditions; therefore, more efforts should be put into the seismic safety of gantry cranes. However, the seismic performance of the gantry crane has been largely disregarded compared with that of bridges and steel moment frames [1,2]. In fact, as the lifting capacity of the gantry cranes continue to increase [3], some research works suggested that many newer cranes may fail during earthquakes because of their larger gauge length and heavier loads [4,5]. The 1995 Kobe Earthquake indicated that the impact of the earthquake on the crane structures cannot be omitted (see Figure 1) and brought up that the cranes with better seismic-resistant behavior in modern logistics systems count for much. In the past few decades, a few research works have been carried out in terms of the seismic behavior of container cranes. [PERSON] et al. [6] first demonstrated the capability of a modern finite element method to capture the dynamic characteristics of a container crane structure. A series of studies in Japan was performed following the Kobe Earthquake [7; 8; 9], which was conducted decades ago. [PERSON] and [PERSON] et al. [10; 11] presented the results of the scale testing and analysis of a typical container crane subjected to earthquake loading. [PERSON] and [PERSON] investigated the dynamic behavior of a container crane subjected to multi-direction seismic load [12]. Furthermore, the active seismic control of crane structures has also been investigated based on the shock absorption theory. For example, [PERSON] [13] developed a five degree-of-freedom mathematical model of a gantry crane to investigate the dynamic behaviors of cranes under seismic effects. [PERSON] and [PERSON] et al. [14; 15; 16] studied the active vibration control of container cranes against earthquakes by varies controllers. These studies have proven that active vibration control has a great potential in cranes for suppressing earthquake-induced vibration [17]. It is notable that all the above research work analyzed the seismic capacity of the cranes based on deterministic analysis (i.e., seismic analyses of the container crane subjected to one or more specific seismic records). For a more precise and reliable result, fragility analysis should be considered for the seismic valuation of the cranes. Fragility analysis is an operational and comparatively mature method [18; 19; 20], which is commonly utilized in conventional structures, such as steel moment-resisting frames [21; 22] and bridges [23; 24; 25], to combine the seismic uncertainties and structural uncertainties in the seismic valuation. Near-field ground motions are described by high velocity and long-period displacement pulses, which have a damaging potential and could result in more serious consequences compared to far-field seismic records [26]. However, to the best of the authors' knowledge, the fragility analysis of the gantry crane has not been reported so far, let alone subjected to near-field ground motions. Based on this situation, this study develops a probabilistic seismic demand model (PSDM) for the first time to further investigate the seismic fragility of a gantry crane and the influence of the seismic incident direction on the structural susceptibility.