직립식 방파제 신뢰성 기반 최적 설계: 활동, 전도, 지반 훼손으로 인한 붕괴 파괴를 중심으로
Reliability-Based Design Optimization for a Vertical-Type Breakwater with an Emphasis on Sliding, Overturn, and Collapse Failure
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초록
우리나라 해안공학계에서 신뢰성 기반설계가 빠르게 체화되는 계기를 제공하기 위해 다 수의 한계상태를지닌 직립방파제 신뢰성 해석과 신뢰성 기반 최적 설계를 우리나라를 대표하는 항이 운영 중인 부산, 군산 전면해역을 대상으로 수행하였다. 이 과정에서 상당한 정도의 신뢰성 해석을 수행하기 위해, 특정 재현 빈도의 설계 파 사용은 지양하였으며, 직립방파제의 파괴 여부를 결정하는 확률변수인 파력, 양력, 전도 모멘트에 내재한 불확실성은장기 파랑 관측자료를 빈도 해석하여 얻은 확률모형을 사용하여 기술하였다. 직립식 방파제의 한계상태는 활동, 전도, 지지력을 고려하여 세 개로 구성하였으며, 파력과 양력, 모멘트 사이의 밀접한 상관성은 Nataf 결합확률분포를사용하여 기술하였다. 모의 결과, 쉽게 예상해볼 수 있듯 활동만을 고려하는 경우 파괴확률이 과소하게 산출되는것을 확인하였으며, 특정 재현 빈도에 근거한 설계 파랑으로는 방파제 파괴확률을 일정하게 담보할 수 없다는 것을확인하였다. 이에 비해 신뢰 지수가 b = 3.5~4를 충족하도록 최적 설계된 방파제는 두 해역에서 모두 균질한 파괴확률을 확보하는 것으로 모의 되었다.
Abstract
To promote the application of reliability-based design within the Korean coastal engineering commu nity, the author conducted reliability analyses and optimized the design of a vertical-type breakwater, considering multiple limit states in the seas off of Pusan and Gunsan – two representative ports in Korea. In this process, rath er than relying on design waves of a specific return period, the author intentionally avoided such constraints. In stead, the author characterized the uncertainties associated with wave force, lift force, and overturning moment – key factors significantly influencing the integrity of a vertical-type breakwater. This characterization was achieved by employing a probabilistic model derived from the frequency analysis results of long-term in-situ wave data. The limit state of the vertical-type breakwater encompassed sliding, overturning, and collapse failure, with the close interrelation between wave force, lift force, and moment described using the Nataf joint probability distribu tion. Simulation results indicate, as expected, that considering only sliding failure underestimates the failure prob ability. Furthermore, it was shown that the failure probability of vertical-type breakwaters cannot be consistently secured using design waves with a specific return period. In contrast, breakwaters optimally designed to meet the reliability index requirement of b-3.5 to 4 consistently achieve a consistent failure probability across all sea areas.
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