Evaluation of Contributing Variables on LRFD Berthing Load Factors

Abstract: Structural design in the U.S. is based primarily on Load and Resistance Factor Design (LRFD), in which demand forces are factored and combined to achieve an acceptable level of reliability for the structure. To accomplish this, statistical analyses must be performed to examine the variability of the loads being considered. Recently, PIANC Working Group 211 (WG 211) published new guidelines for the design of fenders. These guidelines incorporate statistical modeling to determine load factors for berthing energy, considering many variables that impact the selection of the fender.

For the design of fender-supporting structures, the selection of load factors applied to the reaction force must similarly account for contributions from berthing velocity, manufacturer tolerances, fender type, temperature, etc. Currently, existing codes and guidelines lack empirical support for the suggested load factors that govern the design of the structures absorbing fender reaction forces. Consequently, the recommended load factors remain ambiguous, resulting in inconsistent levels of reliability in structural design.

The authors of this paper have previously demonstrated how Monte Carlo statistical modeling can be used to determine appropriate load factors that capture the variability of berthing velocities for the design of fender-supporting structures. Our latest analyses have broadened the application of Monte Carlo modeling to explore additional contributions, such as the impacts of temperature, fender type, and manufacturer tolerance on the selection of load factors.

How does this project / topic contribute to the advancement of the industry and profession?: This research contributes to current work by the Mooring and Berthing Subcommittee developing LRFD load factors in the upcoming ASCE/COPRI Piers and Wharves Design Standard. This research will:
-Better inform engineers and owners of the shortcomings of current fender load factors in existing codes/guidelines, which, to date, have been arbitrarily defined,
-Provide a clear path toward quantifying reliability for the design of fender-supporting structures,
-Showcase ways of handling uncertainties such as berthing velocities and the effects of temperature on fender reaction loads through Monte Carlo statistical modeling, and
-Identify key questions that warrant input from the greater marine engineering community.

Does the project / topic implement new and innovative techniques, materials, technologies, and delivery methods?: Monte Carlo statistical modeling has been established since the mid-20th century across various fields such as mathematics, physics, and economics. These methods have also found application in reliability-based structural engineering. Monte Carlo methods were used to develop LRFD in the United States. Our paper seeks to leverage advancements in computing technology to employ Monte Carlo modeling in the design of fender-supporting structures. Our goal is to create a robust basis for defining LRFD load factors for fender reaction forces, which will directly support the Mooring and Berthing chapter of the upcoming ASCE/COPRI Piers and Wharves Design Standard.

What was the most challenging aspect of your project / topic and how did you handle it to ensure success?: Our greatest challenge has been to develop a methodology that would be concise and straight-forward to apply in engineering practice while also ensuring our methodology has sound statistical basis. The authors are primarily engineer practitioners, not mathematicians and statisticians. As a result, we have leaned heavily on input from academia, code/standards developers, fellow practitioners, and the early authors of LRFD to help develop our theories, vet our procedures, and identify potential shortcomings. We have already engaged several experts to develop the methods presented in this paper. We expect that this body of reviewers will grow and further validate our work.

Who is the target audience for this paper?: The target audience of this paper includes both developers of codes and standards, as well as practitioners who design fender-supporting structures. The methodology proposed in this paper may also apply to adjacent structural disciplines that use LRFD load factors.