The purpose of this study is to present a structural safety assessment of offshore jacket structure against the increasing environmental load. Due to climate change, sea-level rise and strengthening of typhoon power have caused abnormal high-wave phenomenon, and recent earthquake frequency and magnitude are increasing in Korea. Since the offshore jacket structures is generally located in the water space, environmental loads predominate.
The RSR values were derived from the pushover analysis for wind, wave, and tidal load, and the structural safety was evaluated by comparing with the pushover analysis for seismic load. Concluded that the jacket structure is vulnerable to seismic loads and based on this, nonlinear time history analysis was performed.
The results of the nonlinear time history analysis of the jacket structure were evaluated using KBC2016 and Perform 3-D. Based on the results, a weakening part of the jacket structure was found and a reinforcement model was proposed to minimize damage.
The conclusion is as follows
1) The example model of the jacket structure were modeled using the commercial analysis program MIDAS Gen and the earthquake analysis program Perform 3-D, and the safety and behavior were analyzed by performing the pushover analysis and the nonlinear dynamic analysis.
2) As a result of the pushover analysis, the structure was stable for wind, wave, and algae, and the RSR value was 2.56, indicating that the degree of damage was “middle”, However, as a result of the pushover analysis for the seismic load, the leg structure collapsed due to the heavy load on the upper structure, and the weak behavior against the earthquake load was show, and. the RSR value was 1.633, indicating that the degree of damage was “high”.
3) The results of the nonlinear dynamic analysis show that the El Centro earthquake has a stable behavior but the Mexico earthquake has resonance and it is very weak. The structure does not cause the whole plastic behavior and stress concentration phenomenon, and some member local failure mechanism occurred.
4) In order to investigate the plastic behavior of the model against the seismic waves of Mexico, Brace reinforced model was analyzed. As a result, plastic deformation occurred at 50% of the Mexico earthquake acceleration but the seismic performance was IO grade.
5) Through the seismic analysis, it can be seen that the example structure is vulnerable to the long-period wave, and it is desirable to reinforce it with brace to secure the safety of the structure.