Fatigue Performance Analysis Of Reinforced Concrete Structure Strengthened With CFRP Sheets

In recent years, many structures become deteriorate for the increase of loading grades and extension of service years. The deterioration of structures has promoted extensive research efforts to find effective and economical rehabilitation means. One of the emerging technologies that have proven particularly suited for strengthening reinforced concrete (RC) structures is the use of externally bonded carbon fiber reinforced polymer (CFRP) in the form of plates or laminates. Being a new structural material widely applied in strengthening concrete members, information on the short-term behavior is relatively abundant and well researched. But data on long-term behavior, especially fatigue response is rather limited. In this dissertation, based on the test results, two approaches are promoted to predict the fatigue life of RC beams strengthened with CFRP sheets. The reliability of the analysis is compared and testified with test results and the guidelines in codes. Research work conducted in the dissertation is summarized as follow:1. On the basis of assumptions, like plane section, non-bonding slip and non-peeled failure, finite element models are established. The investigation of the performance of RC beams strengthened with CFRP sheets under static and cyclic loadings is carried out by using ANSYS software. The consequently findings of the distribution of stress and strain of steel bar and concrete, the relationship of cyclic loadings and strain of steel bar, the development of fatigue life and stress amplitude, and crack progressing in concrete are presented in the dissertation.2. Numerical simulations of fatigue performance of reinforced concrete slab strengthened with CFRP sheets are worked out by using ANSYS software. The curves of stress-fatigue life and strain-fatigue life of reinforced bar and CFRP sheets under various fatigue loadings are obtained, respectively. Compared the results of numerical simulation with corresponding tests, the coincident trend of fatigue life was found for intact and pre-damaged RC beams strengthened with CFRP sheets, and the stress of reinforced concrete plates conformed to the procedure of three developing stages.3. Nominal stress method is applied for fatigue analysis of reinforced concrete beam strengthened with CFRP sheets. Nominal stress and stress concentration factor are obtained from document [47]. According to the S-N curves provided by domestic and overseas standards and research results obtained by Zheng Zhibin, etc, the fatigue life of strengthened reinforced concrete beam was evaluated and the optimized S-N curves for different steel types were promoted. 4. Local stress-strain method is introduced for fatigue analysis of reinforced concrete beam strengthened with CFRP sheets. According to the related references and test data, parameters and the practicable S-N curve for strengthened reinforced concrete beam were adopted. The practical conclusions for analyzing fatigue life of strengthened reinforced concrete beam were pointed out.