This paper investigates the use of three-dimensional (3D) potential-based fluid elements for seismic analyses of deep water pile foundation. The mathematical derivations of the potential-based formulations are presented for reference. The potential-based modeling technique is studied and validated through experimental data and analytical solutions. Earthquake time history analyses for a 9-pile foundation in dry and different water environments are conducted, respectively. The seismic responses are discussed to investigate the complex effect of earthquake-induced fluid-structure interaction. Through the analyses, the potential-based fluid and interface elements are shown to perform adequately for the seismic analyses of pile foundation-water systems, and some interesting conclusions and recommendations are drawn. 1. Introduction Bridges are popular solutions for crossing gaps caused by rivers, reservoirs, straits, or bays. These bridges usually have long spans and need to be supported by deep water foundations [1]. One of the common choices is using deep water pile foundations due to their low cost and ease of construction [2, 3]. This type of foundation consists of piles, a concrete cap, and piers or towers, where piles and pile cap are usually immersed in the water [4, 5]. Previous research [6–8] showed that the interaction between the structure and the surrounding water might alter the dynamic characteristics, which may lead to additional dynamic forces. The earliest approaches to account for the hydrodynamic force on the cylindrical objects were drawn from experimental data and presented in terms of “added mass” [9]. Although it lacked theoretical derivation, “added mass” is still a widely used concept because of its simplicity [10–12]. The analytical dynamics of cantilever towers in water was then developed mathematically, including structural flexibility and water compressibility effects [13]. Many later investigations followed it and continued to study the fluid-structure interactions of the single immersed cylinder [14, 15]. Although the single pile problem has been studied thoroughly, the pile-group-water interaction is still hard to solve due to the mathematical difficulties in modelling the complex interfaces and boundaries. Rapid development of computer techniques motivated scientists to find numerical methods to overcome those analytical limitations. Numerous approaches based on either finite elements or boundary elements were proposed in the last few years [16, 17]. Potential-based fluid element (PBFE) was proposed in 1980s [18]. Today it
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