A3D Finite Element Approachfor Stress Field Analysis of Mooring Dolphin Pile Caps for Strut-and-Tie Modeling - A Parametric Study with acting Mooring Load

Abstract

A mooring dolphin is a marine structure designed to secure a vessel by mooring lines. These structures are typically equipped with pile caps to accommodate piles, anchors and bollards. Conventionally, a two-dimensional strut-and-tie model (STM) is used in the design of mooring dolphin pile caps. This thesis proposes an alternative design methodology involving the development of a three-dimensional finite element (FE) model for a specific mooring dolphin. This approach aims to mitigate the uncertainties arising from the assumptions inherent in traditional two-dimensional STM applications. Furthermore, the three-dimensional model was processed using a self developed computational script, to sort and vi sualize principal stress tensors, enabling the systematic mapping of the internal strut-and-tie network within the structural volume. The script also includes the possibility of drawing the struts and ties directly within the structural volume and its stress field. The assessed mooring dolphin was analyzed for self-weight combined with four moor ing load directions, and varying pile cap thickness and anchor length. When sub jected to the mooring load, the expected structural response was simultaneously piles in compression and anchors in tension with struts stretching in between the pile plate and anchor plate. This was confirmed and the analysis revealed that the magnitude of the struts and ties changed with the mooring load’s inclination, while their configuration remained intact. The three-dimensional FE model provides a comprehensive visualization of the global internal stresses within the pile cap and thereby can be used as guidance for the derivation of strut-and-tie models. Although this approach may reduce uncer tainties regarding the internal stresses, it remains dependent on the design engineer to connect and map the nodes. To address this, in this thesis, a set of guidelines were established to support the engineer through these decisions.