In this paper, case studies were carried out to analyze the feasibility of submerged floating tunnels (SFTs) with suspension cables. In order to apply an SFT in a field site, the deformation of the system should be controlled, even under extreme wave conditions, if vehicles or trains operate inside the SFT. Two types of suspended SFTs were proposed to analyze their hydrodynamic behavior. The main variables were the wave conditions, cross-sectional diameters, buoyancy weight ratios, inclination angles of the main cables, and installation depth of the SFT. Overall, it was found that the SFT with a mid-anchor was superior from a hydrodynamic point of view. However, a detailed hydrodynamic analysis must be performed to avoid the conditions that previously produced slack. In addition, in a case where acceleration is generated by motion, the design should be reviewed to ensure safe conditions, according to the traffic passage.

This paper presents an experimental study of the behavior of a steel-composite hollow reinforced concrete (RC) column under concentric loading. The effects of important variables, such as concrete strength, inner tube thickness, hollow ratio, column diameter, and transverse reinforcement space, are presented in this study. The failure of composite hollow RC columns is characterized by the formation of an inclined shear sliding plane. When the column had a highly confined effect, the inclination of the shear sliding plane was 45°. This study shows that the required performance is achieved when the splice providing transverse reinforcement is fully bonded. Furthermore, the inner tube experiences buckling failure after reaching its maximum strength. The steel-composite hollow RC column with high-strength concrete (HSC) has lower ductility and toughness compared to a column with normal-strength concrete (NSC).

This paper presents a design for a movable barrier on the revetment of the Haeundae Marine City in Busan, the Korea. This movable barrier was developed to use as a tourist deck in a normal state and to block wave overtopping in an abnormal state. To carry out the physical experiment in a wave flume, the model structure was reduced to a scale of 1/36 compared to the field structure. The discharge of the wave overtopping, the uplift pressure acting on the under surface of a non-standing barrier, and the wave pressure acting in front of a standing barrier were measured to analyze the hydraulic characteristics of the movable barrier. The results show that the impulsive pressure acts on the movable barrier, although the overtopping discharge is less than the allowable limit. When designing a movable barrier at a full scale, engineers should consider the impulsive pressure to secure the barrier’s stability on the target site.

Submerged floating tunnels with suspension supports (SFTSS) resemble to suspension bridges on lands, which are installed a number of hangers on the main tower and main cables to support the girder. On the other hand, as the SFTSS installed underwater has to resist the buoyancy and the forces in an offshore environment, the main cable was installed at the bottom of the tunnel body and connected with a hanger. The concept of the SFTSS was first proposed by Won et al (2019, 2022). It was found that the SFTSS was generated itself a tuned mass damper (TMD) effect due to the interaction between the body and the main cable. This can induce the vibration of the body to be attenuated according to the offshore environment conditions such as waves and currents, and had a feature that the length between the main towers can be longer than 3 km (Won et al., 2022). The body of the SFTSS was supported by main cables and hangers as aforementioned. In case of the hanger was down by failures, the behavior characteristics of the SFTSS would be changed and be greatly reduced the structure safety. In this study, the behavioral characteristics of the SFTSS were analyzed according to five scenarios on the cable failure.

The foundations of offshore wind power can be classified as floating, tripod, jacket, monopile, or gravity-based, depending on the support type. In the case of tripod- and jacket-type supports, the structures require precise construction. There are two main methods for installing substructures: post- and pre-piling. The post-piling method involves moving the completed substructure to the site and fixing it to the seabed by inserting a pile into the leg pile and driving it, allowing it to be constructed without special off-shore equipment; however, the construction period is long. Contrarily, the precision of foundation installation can be improved by installing a pre-piling template, which is special equipment that serves as a basic structure, on the seabed in advance, and subsequently inserting substructures. This study presents a new type of underwater pre-piling template and method for achieving optimal construction environment conditions. Construction precision was analyzed based on the wave condition, current speed, winch speed, wave direction, and current direction while the under-water template was anchored to the seabed. It was found that the wave conditions, winch speed, and vessel type had a significant influence. The results obtained considering the Douglas sea scale show that precise construction could only be achieved within Grade 2 for general barge ships, while jack-up barge ships could be used even at Grade 3 or higher. The higher the winch speed, the more stable construction becomes possible, and jack-up barges show greater constructability than general barges.