Design of post-tensioned segmental offshore structures

The continuous increase in global energy demand has heightened the need for innovative approaches in the construction technologies of offshore platforms. A notable example of this innovation is the Condeep-type offshore platforms, which have been successfully implemented in Norway. These platforms are constructed using high-strength materials such as high-strength concrete and steel. Typically, these platforms are manufactured monolithically on land and transported to their installation sites using barges, making it critical for these structures to be lightweight and portable during the manufacturing process. Therefore, this study aims to employ prestressed and segmental techniques in the design of Condeep-type offshore oil and gas platforms to facilitate their more economical, easier, and safer construction in deep waters. In the first part of the study, the effectiveness of circular prestressing on the structure was investigated using advanced analytical methods. Subsequently, in the numerical modeling section, the experimental results obtained from the literature were compared with analyses conducted using DIANA finite element software, leading to the selection of the most appropriate finite element type for use in the design. Here, the experimentally determined load-displacement behavior of reinforced concrete, prestressed, and segmental prestressed beams was compared with the results of finite element models created using one-dimensional beam, two-dimensional shell, and three-dimensional solid element types. It was found that the three-dimensional solid modeling provided results that were closest to the actual structural behavior. Following this, dynamic analyses incorporating fluid-structure interaction were performed using the selected element type. These analyses demonstrated that the modal frequencies and mode shapes of a cylinder under water and vacuum conditions, as obtained from the literature, could be determined with high accuracy. In the second part of the study, a parametric analysis was conducted using the finite element model developed based on the results from the first part, with the aim of examining the structural behavior of segmental structures. This parametric study investigated the effects of variables such as concrete compressive strength, number of segments, and crack models on the shear strength, joint strength, ductility, and crack width of the segmental structure. In the final part of the study, a new segmental analysis and design approach for offshore platform design was proposed. This section thoroughly examined the monolithic and segmental design of segmental structures and explored how structural performance is affected under offshore conditions. This study aims to develop a modular construction methodology to build safer, more efficient, and more adaptable offshore platforms.