Rational Treatment of Simultaneous Berthing and Mooring Load Effects on the Design of Oil Docks

Abstract: A critical gap exists in current guidelines regarding the treatment of simultaneous berthing and mooring loads on pile-supported oil docks. In double-sided berthing structures such as "island" type docks (loading/unloading platforms with a series of isolated breasting and mooring dolphins) or narrow finger piers, which are very common in the industry, existing design provisions lack clarity and do not properly address such conditions.

The development of load combinations is of particular concern. For simultaneous berthing and mooring loading conditions, a load factor of 1.6 is arbitrarily imposed separately on both, as dictated by prevailing marine standards such as MOTEMS (2022) or PIANC 153B (2022). If berthing and mooring are expected to occur simultaneously, applying this factor to both load scenarios could lead to an overly conservative design, especially for flexible structures or structures with limited piles. The situation is aggravated if quick-release hooks (QRHs) are present. Existing provisions in MOTEMS and PIANC Guidelines call for the imposition of an additional load factor, which, despite accounting for the benefit of multiple hooks in this type of assembly, further adds conservatism to the design process.

This paper addresses this critical issue by presenting a theoretical evaluation and rational treatment of the problem using a case study to highlight the complexities associated with designing these types of structures for concurrent berthing and mooring loads. Through careful analysis and engineering judgment, the paper proposes alternative load combinations tailored to the specific configuration of the structure, thereby advocating for a more nuanced and practical approach to design in such scenarios. By shedding light on this overlooked aspect, the paper aims to promote further discussion and refinement of design guidelines in the presence of multiple loading sources within the marine engineering community.

How does this project / topic contribute to the advancement of the industry and profession?: This topic addresses the lack of guidance within current marine standards such as MOTEMS (2022) and PIANC 153B (2022), particularly concerning loading conditions in double-sided berthing scenarios, such as those encountered in "island" type docks and finger piers. Highlighting this gap underscores the imperative need for the marine industry to establish a standardized framework to assist engineers in designing such structures. Furthermore, it initiates a discussion to illuminate past solutions pursued by professionals.

Does the project / topic implement new and innovative techniques, materials, technologies, and delivery methods?: The topic innovatively addresses the absence of guidance in existing standards on treating simultaneous berthing and mooring loads by devising a new, rational methodology to tackle overly conservative loading combinations. Through thorough analysis and current guidelines investigation, the authors developed a rational solution that further refines existing standardized design approach recommendations.

What was the most challenging aspect of your project / topic and how did you handle it to ensure success?: The absence of guidance to deal with simultaneous berthing and mooring loads on island-type docks and narrow finger piers is the most challenging aspect of the topic. We address it with a rational approach, considering not only site conditions but specific operator's needs. Because load combinations are often developed from data on the uncertainty of loads, the lack of data and guidance enhances the challenge. To ensure success, we perform thorough analysis, apply engineering judgment, and collaborate with industry peers.

Who is the target audience for this paper?: The paper's target audience involves Designers, Owners, and Marine Terminal Operators within the marine engineering industry. Given the prevalent occurrence of simultaneous berthing and mooring loads, especially in structures like island-type docks and finger piers, these stakeholders may encounter the challenges outlined in this paper regarding the design clarity of simultaneous berthing and mooring.