## 1 Introduction  
Earthquakes are a natural phenomenon resulting from sudden movement of the Earth's crust generated by plate movement or volcanic activity. The frequency of earthquakes above 6 on the Richter scale did not increase during 2000-2021 in comparison with previous decades (Figure 1); however, the United Nations estimated that earthquakes caused the deaths of 750,000 people in 1998-2017 (Figure 2). Therefore, earthquakes are more deadly and destructive than other types of disasters.  
Earthquakes can involve strong shaking of the ground and generate seismic loads in structures that may cause enormous damage to buildings. This is the main reason why people become trapped in buildings or are injured or killed by falling buildings during earthquakes. Moreover, damage to water tanks during earthquakes is a major problem, as it can decrease supplies of water for drinking and for firefighting. Therefore, firefighting water tanks must remain functional after earthquakes.  
In recent years, countries worldwide have endeavoured to improve the strength of buildings to reduce loss of life and property during earthquakes. As a result, new design standards have been introduced in engineering to ensure that buildings exhibit good seismic performance, especially firefighting facilities. In line with this global trend, in 2021, the National Fire Agency in the Republic of Korea announced the adoption of the 'Amendment to Seismic Design Standards for Fire Facilities', which encompasses requirements that have been continually promulgated since January 2016. In addition, in 2022, the 'Korean Building and Structure Code' was revised. Both of the aforementioned documents require the structural integrity of firefighting water tanks to be assured via assessment of their seismic performance.  
Under seismic loads, the principal modes of water tanks include a short-period impulsive mode and several long-period convective (sloshing) modes. In most water tanks, the former mode dominates the loading on the tank wall and the latter modes are much less prominent. A short-period impulsive mode often severely damages a water tank by causing  
Figure 1: Statistics of worldwide earthquake 2000–2021 [1].  
Figure 2: Number of deaths per disaster type 1998–2017 [2].  
shell buckling, roof warping, and supporting system and foundation failure. Thus, there is a need for a method that can numerically model firefighting facilities, including water tanks, under seismic loads and in accordance with the revised design codes, thereby allowing the design of devices to mitigate the pressure on water tank walls during earthquakes.  
The aim of this study was to develop numerical modelling methods to simulate the effect of an anti-wave plate on liquid sloshing in and the strength of a firefighting water tank. Three numerical modelling methods were developed: a quasi-static structural modelling method, a transient structural modelling method, and a one-way fluid-structure interaction (FSI) modelling method. The quasi-static and transient structural modelling methods simulate the structural responses of a water tank under zero period acceleration and seismic time histories of acceleration, respectively, and treat the fluid in the tank as a solid volume. The one-way FSI method simulates the effect of the anti-wave plate in a water tank on liquid sloshing in the tank. Here, the pressure induced by liquid sloshing in a tank was numerically calculated and directly applied to the inner wall of the tank. The effect of the anti-wave plate on the pressure acting on the water tank wall was simulated in three scenarios: without an anti-wave plate, with a 50%H anti-wave plate, and with a 70%H anti-wave plate (where 'x%H' means the anti-wave plate height was \(\approx\)% of the tank height). The scenarios examined in the numerical simulations are summarised in Table 1.