Stochastic Fatigue Assessment for Berthing Monopiles in Inland Waterways

Abstract

As an unsupported structure, a berthing monopile is often expected to work under harsh conditions. Approaching vessels may introduce considerable berthing energy, resulting in substantial tensile stress on the pile. This vessel impact occurs frequently as a primary load over the service life of the berthing monopile. In this situation, the fatigue safety of circumferential butt welds on piles becomes a crucial aspect in monopile design. This paper evaluates linear elastic fracture mechanics (LEFM)–based fatigue reliability for circumferential splice welds on steel monopiles. Studied monopiles are those installed in inland waterways, for which the predominant fatigue loading is vessel berthing. Important factors involved in the fatigue reliability assessment are addressed. A geometry function for determining the range of stress intensity factor is identified, an approximate stress concentration factor for piles under bending moment is mathematically formulated, and the beta distribution is applied to characterize the doubly bound hot-spot stress range caused by operational water-level constraints. A detailed case study is presented for illustrative purposes. This paper provides a practical approach to assessing LEFM–based fatigue reliability for steel berthing monopiles.