Tensile fatigue behavior of UHPECC and application of FRP-reinforced UHPECC for offshore storage tanks

Abstract

With climate change driving higher sea levels and more frequent extreme weather occurrences, coastal megacities are facing a growing scarcity of land. On the other hand, the demand for infrastructure to support urban economic development is increasing, intensifying the conflict between land supply and infrastructure needs. Developing and utilizing ocean space is emerging as a viable solution. The development of high-performance and durable marine infrastructure is of great significance to the economic advancement of coastal cities. However, marine environments present conditions that are much harsher than those on land. Structures are subjected to long-term effects from wind, waves, and currents while being exposed to a highly corrosive environment. Widely used steel-reinforced concrete and steel structures inevitably suffer from corrosion. The combined effects of loading and corrosion can significantly reduce the safety and durability of these structures, posing considerable challenges for the development and application of marine engineering. To address the aforementioned issues, the development of marine infrastructures using high-performance materials has emerged as a significant field. This thesis aims to explore the feasibility of two emerging materials, Fiber Reinforced Polymer (FRP) and Engineered Cementitious Composites (ECC), for use in marine infrastructure applications. The research employs polyethylene (PE) fibers and a high-strength cement matrix to create ultra-high-performance Engineered Cementitious Composites (UHPECC) with high tensile strength and deformation capacity. Initially, the fatigue performance of UHPECC under different load conditions is investigated through experiments, considering variables such as stress levels and loading frequencies. The influence of initial static tensile strength is also introduced, and a probability of failure-stress level-fatigue life (P-S-N) model is established using data from tensile fatigue tests. Subsequently, to account for the stress ratio, particularly the influence of stress reversal on fatigue life, an additional set of fatigue load tests under different stress ratio conditions was conducted. The adverse impact of a negative stress ratio on the fatigue life of ECC was examined. A cumulative fatigue damage model was developed based on the fatigue deformation history of the specimens to assess fatigue damage under various loading conditions. At the component level, this study investigates the mechanical performance of flexural members made of UHPECC reinforced with FRP bars, which are particularly suitable for marine infrastructure. These novel structural members offer the following advantages over steel reinforced members: (1) steel corrosion is completely avoided by replacing steel bars with FRP bars; (2) the tensile strength of FRP reinforcement could be completely utilized due to the ultra-high strength of UHPECC; (3) UHPECC’s high ductility and tensile toughness ensure excellent deformation compatibility with FRP bars; (4) using locally available sea sand dramatically reduces the transportation cost and energy consumption. To demonstrate the above advantages, FRP-reinforced UHPECC beams were fabricated and tested. The influences of FRP reinforcement ratio, fiber dosage of UHPECC, and loading scheme on the behaviors of the beam specimens were investigated in detail. The crack development in UHPECC, load-displacement responses, failure modes, energy dissipation capacities, deformation capacities, and strain evolutions were measured and discussed. The test findings demonstrated that the incorporating of fibers significantly reduces the relative slip between FRP and UHPECC, enhancing the deformation capacity of the specimens. However, cyclic loading damages the fibers’ bridging effect, thereby reducing the performance of the specimens. On the structural scale, this study proposes an offshore placement scheme for storage tanks, a widely used industrial structure, to achieve large-scale storage. The newly proposed offshore storage tank can remain stable in a marine environment, and its feasibility is verified under various potential failure scenarios. The research subsequently examines how hydrodynamic pressure is distributed across the cylindrical shell of the storage tank as a result of wave loads, and it determines the stresses induced in the shell by these wave loads. The findings reveal that the ultimate stress levels of the proposed structures fall within the range that the new materials can withstand. This preliminary evidence confirms the feasibility of using these emerging materials in marine infrastructure applications. Finally, the conclusions are outlined and suggestions for future research are emphasized. Overall, the developed work provides a foundational exploration into the application of emerging materials in marine infrastructures.