Effective Stress Drydock Analysis
Final rept. Jul-Sep 98
NAVAL FACILITIES ENGINEERING SERVICE CENTER PORT HUENEME CA
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Recent earthquakes have emphasized the high damage threat the soil liquefaction phenomenon poses to water-front structures. These experiences have shown that both the nature of waterfront facilities, such as earth-retaining structures, and the depositional environment of the coastal marine soil contribute to major liquefaction damage. Drydocks are critical structures containing high value ships and as such represent a class of structure which can not fail during an earthquake. Consequently, drydock certification studies have been conducted to evaluate the safety of drydocks under all possible load conditions. The recent development of effective stress finite difference technology now permits a more accurate assessment of these structures. The newly developed FLAC computer program was evaluated as part of this study and a demonstration case performed on the drydock located at Naval Station, San Diego. The results of this study show that the drydock has adequate factors of safety for the static load considered. This is in agreement with the drydock certification study. This analysis shows the drydock to be at yield levels during dynamic earthquake loading. The levels of liquefaction are limited and controlled. The FLAC analysis is better able to represent the actual loading conditions on the drydock than the traditional hand calculations performed in the drydock certification studies. As a result the more accurate FLAC analysis shows a lower level of loading both under static and dynamic conditions and higher factors of safety. The conclusion of this study is that for the conditions established in the drydock certification report, the drydock is safer than indicated in the report under dynamic loading.
- Marine Engineering
- Structural Engineering and Building Technology