Session: 06-01-01 Computational Mechanics and Design Applications

Submission Number: 181041

Nonlinear Static Behavior of a Deep-Water Jacket Incorporating Steel–UHPC Composite Legs 

Deep-water jackets must resist long-term cyclic loading and episodic extremes; consequently, fatigue remains a governing design concern, and severe storms challenge global integrity and reserve strength. Concrete-filled steel tubular (CFST) concepts—well established for onshore structures—provide a promising approach to mitigating these issues by combining high stiffness and strength with superior durability. This work investigates a composite-leg jacket scheme in which conventional tubular legs are replaced by steel–UHPC(Ultra-High Performance Concrete)–steel sandwich tubes—concentric steel tubes with a UHPC core—to enhance system-level performance and durability. A real engineering jacket is adopted as the case study, with the original steel-leg configuration retained as the baseline for comparison.

A refined nonlinear finite-element model is developed in OpenSees. At the component level, the response of steel–UHPC–steel sandwich tubes is benchmarked against published experimental databases to calibrate steel and UHPC constitutive parameters. At the system level, the jacket’s linear baseline (with material and interaction nonlinearities excluded) is verified against SACS. Building on this baseline, nonlinear analyses incorporating steel and UHPC material nonlinearity and the steel–concrete composite constraint effects evaluate (i) nonlinear static performance, (ii) dynamic responses under operational sea states, (iii) full life-cycle fatigue performance following standard offshore practice, and (iv) extreme-event behavior (ultimate strength/ductility) under design-level hazards.

Results indicate that the composite-leg jacket exhibits improved elastic performance, along with reduced dynamic amplification, enhanced local stability and higher collapse margins under extreme loads. Fatigue demand at critical hot spots is consistently lower, supporting longer life-cycle fatigue performance relative to the steel baseline. Overall, the composite-leg scheme delivers meaningful system-level gains in strength, dynamics, and fatigue, improving safety, extending service life, and enhancing life-cycle value for deep-water jacket structures.

Presenting Author: Xiaolong Zhao Tsinghua University

Presenting Author Biography: Xiolong Zhao is a Ph.D. candidate in Ocean Engineering at Tsinghua Shenzhen International Graduate School. His research focuses on steel–concrete–steel (SCS) sandwich structures and the analysis and design of fixed offshore platforms. He is proficient in modeling and numerical simulation with Abaqus, OpenSees, and SACS. His recent work explores the engineering potential of composite (SCS) structures for fixed platforms.

Authors:

Xiaolong Zhao Tsinghua University
Yutao Guo Tsinghua University