Applicability of Concrete–Steel Composite Piles for Offshore Wind Foundations

Offshore wind-turbine support structures are largely made of steel since steel monopiles have accounted for the majority of installations in the last decade. As turbines become bigger, steel structures have led to an exponential increase in material and installation costs. From this point of view, the use of concrete for future support structures has been initiated. In this study, concrete–steel composite piles have been investigated. A pre-tensioned high strength concrete pile was placed in the lower part, mainly to support the axial load, and a steel pile in the upper part to resist the lateral load. A mechanical joint was adapted to connect the two different types of piles. Static axial, dynamic axial, and lateral load tests were performed to evaluate the load-displacement response of the composite pile, verify the integrity of the mechanical joint, and investigate its potential application to offshore wind foundations. This paper focused on the load-displacement response and the connection integrity; in particular, it investigated the lateral load-displacement response by comparing it to the results of beam-spring analysis. Based on the results from the field tests, a site-specific lateral load-displacement curve was suggested, and the connection integrity was verified.