Study On Long-Term Performance Of Pultruded FRP For Ocean Applications

In ocean environment,construction materials are corroded seriously,such as reinforced concrete and steel,while FRP(Fiber Reinforced Polymer)is more suitable with advantages of light-weight,high-strength,corrosion-resistant,and easy construction,etc.Research presented in this thesis focuses on the long-term performance of pultruded FRP in ocean environment by means of mechanism analysis,experiments on material and components,and research on structural application.Moreover,a design method for the long-term performance of FRP in ocean environment considering thickness and time was proposed.The main work and achievements are as follows:(1)A literature survey was conducted on the application of FRP in structural engineering,and two bridges were selected for field research.Maoyisheng Bridge(a pure FRP truss structure)and Dongshuimen Bridge(containing a pure FRP boardwalk)have maintained good performance after several years of service.Literature research also found that FRP structure was increasingly popular especially in extreme environment.The survey and the research confirmed the feasibility and reliability of FRP for long-term application.(2)A review and analysis of the aging conditions in ocean environment,the corrosion mechanism of FRP under these conditions and the prediction methods of longterm performance were conducted,which revealed the basic aging law of FRP in ocean environment.Aging conditions in ocean mainly include water immersion and ultraviolet radiation.The performance degradation of FRP is mainly controlled by matrix,fibers and the interface between them.The corrosion occurs by means of molecular permeation,chemical erosion,and atmospheric erosion,etc.In this way,the prediction methods of long-term performance depend on the selection of acceleration model,aging model,and corrosion failure criteria.(3)The accelerated aging test on FRP material was conducted,for which the aging conditions included high-temperature water immersion,wetting and drying cycles,and ultraviolet radiation.The results showed that the condition impacts on FRP materials were limited in all aspects,and the performance loss tended to be moderated,except for the condition of high-temperature water immersion.Moreover,the temperature setting in water immersion was far higher than normal,and it could be inferred from the results that the performance in normal use would be better.Therefore,the durability of FRP material is good in ocean environment.(4)The accelerated aging test on FRP components was conducted,for which the aging conditions included artificial seawater immersion and ultraviolet radiation.The results showed that no obvious changes occurred in mass,surface hardness or bearing characteristics of FRP pultruded square tube under both conditions.The bearing capacity loss mainly occurred from 30 to 60 aging days,and the flexural bearing capacity was stable at 80% of the initial value after 60 aging days.The stiffness of components under both conditions remained unchanged with the increase of aging time.Therefore,the durability of FRP components is good in ocean environment.(5)The performance degradation rules of material and components in ocean environment were compared,and the correlation between them was analyzed.The results showed that the performance degradation of the material was higher than that of the component,and a great difference between working conditions was existed.The longitudinal flexural modulus,transverse tensile strength and modulus of material have the main control effect on the flexural performance of component.(6)A design method for the long-term performance of FRP in ocean environment considering thickness and time was proposed,which was combined with the long-term consideration in existing design method,the form of hydrolysis and photolysis dynamic equilibrium equation,and the residual strength model.The design method was well fitted and verified by the testing data of material and components.Research above shows that FRP has a good long-term performance in ocean environment,which provides theoretical support and a design method for its application in ocean engineering.