Sensitivity Study of Dynamic Response and Seismic Performance of Offshore Tripod Structure under Variation of Center of Gravity Location

Hidayat, Novan Arif (2025) Sensitivity Study of Dynamic Response and Seismic Performance of Offshore Tripod Structure under Variation of Center of Gravity Location. Masters thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

An effective weight control is critical for managing gravity loads and the center of gravity (CoG) evolution in offshore platforms. International standards, including ISO 19901-5:2021, require that CoG shift envelopes—defined in two-dimensional (X–Y) and three-dimensional (X–Y–Z) coordinate systems—be considered when assessing pile foundation capacity and global structural behavior. This study examines the influence of CoG uncertainty on the dynamic and seismic performance of a three-legged fixed offshore structure (tripod), which is characterized by slender geometry and long natural period. These characters make it particularly sensitive to gravity loads, lateral forces, and soil variability. A systematic sensitivity analysis was performed using 75 CoG shift cases, spanning four directional quadrants in both 2D and 3D, and including scenarios with up to 20% added topside operating mass. Dynamic and in-place analyses incorporating pile-soil interaction (PSI) were conducted using SACS software. Seismic performance was evaluated through response spectrum–based equivalent static methods. The results show that combined CoG shifts and weight increase significantly amplify structural response, particularly under in-place conditions, which exhibited greater sensitivity than seismic loading. The study identifies a CoG shift envelope that maintains acceptable structural performance and recommends its adoption in future design and modification planning. Emphasis is placed on active CoG management and the necessity for future non-linear assessments to capture post-elastic behavior and ensure the robustness of tripod platform design.

Item Type:	Thesis (Masters)
Uncontrolled Keywords:	center of gravity, dynamic response, natural periods, offshore tripod structure, seismic performance, sensitivity study
Subjects:	T Technology > TC Hydraulic engineering. Ocean engineering > TC1680 Offshore structures
Divisions:	Faculty of Marine Technology (MARTECH) > Ocean Engineering > 38101-(S2) Master Thesis
Depositing User:	Novan Arif Hidayat
Date Deposited:	21 Jul 2025 05:31
Last Modified:	21 Jul 2025 05:31
URI:	http://repository.its.ac.id/id/eprint/120248

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