Investigation of behavior of offshore structures under the effect of external loads

Offshore structures are the types of structures used in the exploration and extraction of energy resources that exist in marine environments, in the generation and discovery of renewable energy potential. In addition to being very versatile; offshore structures are of great importance as they provide alternatives to essential needs. It can be used in different forms such as oil, natural gas platforms, wind turbines, research stations. Due to the environment in which they are located, these structures can be exposed to harsh environmental conditions. These structures are designed and built to withstand environmental conditions, and their designs can be safe and long-lasting by taking into account wave load, wind load, earthquake load and current load, platform features, ground structure. With today's technology, analysis and optimization of offshore structures can be realized thanks to software. In this thesis, the behavior of two fixed jacket-type offshore platforms under external loads was examined. The platforms have a space-frame system and are modeled using cross bracing elements with ANSYS finite element program. The behavior of 34.5 m and 106.5 m 2 offshore structures under wave, wind and earthquake load has been examined by considering 4 different cross elements. When performing the earthquake analysis, 5 acceleration-time data obtaining from stations of the 6 February 2023 Kahramanmaras-Pazarcik earthquake was used. In the wave analysis; airy wave theory was used and analysis were carried out by considering wind load. The study consists of 5 main sections. In the first section, information is given about the external loads that affect the structure such as offshore structures, types, earthquakes, waves, currents and winds. In the second section, information about some of the studies in the literature is given. In the third section, information about the characteristics of the models examined in the thesis study and the earthquake, wind, wave parameters to be used in the analyzes are given. The values and reviews obtained from the results of the analysis are in the fourth section and the results obtained from the reviews in the fifth section.