# Safety Evaluation of a RC Structure with Multiple Openings under High Water Depth Inundations
## 1 Introduction  
Natural disasters are major threats to urban areas, including droughts, earthquakes, hurricanes, inundations, tornadoes, tsunamis and volcanic eruptions [1, 2, 3, 4, 5]. Heavy rainfall may induce inundations to occur in coastal and riverfront zones close to which populated areas often exist [2]. Inundations cause considerable economic and social costs [1]. Risk assessment is often taken advantage of to reduce such costs [6]. Different assessment approaches have been proposed and examined according to risk types, disaster size, flow types and assessment concerns [7, 8, 9, 10, 11, 12, 13]. It is helpful to take into account recurrence intervals for the accurate estimations of flood risk levels [14]. However, risk assessment may not be accurate when the data of past floods are not sufficient [15]. The studies of the behaviour of structures under inundations often consider water depths and duration as damage controlling parameters [16]. The actions of inundations on structures are categorised into five types: hydrostatic, hydrodynamic, erosion, buoyancy and debris actions [16, 17, 18, 19, 20, 21, 22]. As for high-tide floods including tsunamis, in addition to the above-mentioned five actions, impulsive actions need to be taken into account [23]. Wave-text tests showed that forces acting on buildings were highly influenced by flow angles to buildings [24], building shapes [25, 26] and building arrangement [27]. According to the flow angles, forces can be 10 times larger than hydrostatic pressures normal to a building surface [28]. Impact pressures due to impulsive actions were found to be distributedlinearly in a vertical direction [29]. The impact pressures could be 10-12 times higher than the hydrostatic pressures [30]. Analytical and numerical studies have been carried out to examine behaviour under inundations. Two load combinations are usually considered for structural analysis [17; 31]. One assumes that the loads consist of hydrostatic and hydrodynamic pressures [32]. The other considers that the loads are divided into hydrostatic, hydrodynamic and impulsive forces [33]. Hydrodynamic analysis may show accurate results by taking into account accumulative effects due to a series of floods [34]. The behaviour of concrete structures was influenced by interaction between flows and buildings [35]. Debris flows were highly influenced by building density [36; 37]. Impact pressures increase in the vertical and horizontal direction as the water depth increases [29]. Microscale numerical analysis showed that the stresses in concrete specimens were irregularly distributed even under hydrostatic pressures due to the heterogeneity of concrete at microscopic levels [38]. In addition to structural safety, the waterproofness of buildings is a key concern during and after the occurrence of inundations [20; 33]. Waterproof construction techniques were discussed for masonry structures [39; 40] and for concrete structures [22]. Recently, experimental investigations were performed to identify the causes of the waterproofing failures of concrete structures [41]. Experiments showed that cracks were the major factor in water leaks for concrete structures [42]. Concrete bonding waterstops were found to be useful to improve the waterproofness of buildings [43]. This paper proposed a prototype two-storey residential building that is safe against inundations of a 3-m water depth. The ground-storey is built of reinforced concrete (RC) and the first storey of timber. The present research focused on the behaviour of the ground-storey under hydrostatic and hydrodynamic pressures. To this aim, the research consisted of three tasks. First, three-point bending tests were conducted on laminated glass and PMMA plates that were used for windows of the prototype building. Second, a full-scale specimen was subject to hydrostatic pressures of a 3-m water depth. The specimen included a door and windows of the prototype building. Hydrostatic pressures were applied by filling water inside the specimen.