3-Dimensional Nonlinear Static Analysis for Waterfront Structures with Torsional Response under Seismic Loading

This paper presents a methodology to analyze waterfront structures using a 3-dimensional nonlinear static (pushover) analysis to capture the torsional response caused by the eccentricity between the center of mass, and, the centers of stiffness and strength. Waterfront structures often exhibit torsional responses under seismic loading due to the mass and stiffness eccentricity caused by the sloping ground between the nearshore and offshore ends of the structure. The torsional response is further intensified when the structure exhibits an irregular geometric configuration. Typical practice is to analyze these structures using an elastic modal response spectrum analysis, which relies on the equal displacement assumption, that states the inelastic displacement demands can be approximated using an elastic analysis. This assumption may or may not be accurate depending on the extent of nonlinearity in the structure, and the method used for equivalent linearization. The proposed 3-dimensional nonlinear static pushover analysis methodology accounts for the varying eccentricity with displacement demand as yielding of the structure and soil occurs and provides a more direct analysis based on the well accepted nonlinear static methodology. The methodology will be presented as a case study based on marine loading platform analysis and design for the Puget Sound Energy (PSE) Liquified Natural Gas (LNG) Bunkering Facility located in Commencement Bay on the Blair-Hylebos peninsula in Tacoma, Washington.