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Title: Vibration Monitoring of Retrofitted RC Frames Using GFRP
Authors: Vimuttasoongviriya, Atiwat
Supervisor: Kumar, Maneek
Kwatra, Naveen
Keywords: GFRP;Retrofitted RC Frames
Issue Date: 2-Nov-2011
Abstract: The need for structural damage identification is continuously growing to monitor the damage of existing civil structures. The information of damage identification is utilized to make decisions on maintenance of damaged structure. Detecting structural damage using the information contained in vibration signatures has become more widely accepted by many researchers. In high seismic region of north India, existing reinforced concrete buildings have been constructed at time when seismic zones were not recognized. Therefore, these buildings need to monitor the damage and improve their load carrying capacities for the purpose of seismic safety. The Fiber Reinforcement Polymer is one popular strengthening technique. This material with epoxy resin has received considerable attention due to its high strength, light weight, easy manageability on-site and high resistance against corrosion. This paper intends to investigate the effect of lateral loads on nonlinear behavior and the damage identification of retrofitted RC frame models. Vibration based damage identification namely modal plastic softening damage index, stiffness-mass ratio damage method, modal flexibility damage index and frequency response function based mode shape method were used. The three story reinforced concrete moment resisting frame model was constructed and tested under lateral quasi-static loads to simulate different damage states on the structure. The damaged frame was repaired by using Glass Fiber Reinforced Polymer (GFRP) sheets to increase load resistance capacities of structural elements and beam to column connections. Failure mechanism of the experimental frame model has been investigated. The effects of GFRP wrap have been reported. Subsequently, the damage indexes based on the change in dynamic characteristics were investigated using OROS software program with the help of impact hammer excitation test. Finite element (FE) models, nonlinear and dynamic analysis, were used to model experimental frames. Finally, the identification methods based on measured modal parameters, Modal Assurance Criterion (MAC) and Coordinate Modal Assurance Criterion (COMAC), were utilized and the efficiencies of these methods were investigated. Results of this study show that the use of GFRP wrapped for structural retrofitting provides increased significant lateral load capacity and ductile behavior. The damage indices of retrofitted frames reduce indicating better performance as compare to the control frame. Damage indices based on the change in frequency response function shows a much acceptable accuracy correlation with damage based on the change in natural frequency. For FE models, the nonlinear FE analytical results exhibit similar trends with those of the experimental frame model, but the FE model is slightly stiffer than the experimental model. Moreover, the comparisons between the results of dynamic FE model and the experimental results show reasonable accuracy of modal parameter identification. The results of FE model of vibrating frame specimens agree with the experimental results. The MAC is subjected to very small change by damage of retrofitting. This factor cannot determine the stiffness changes in each degree of freedom, but it can present information about overall stiffness change of the structure due to damage or retrofitting. It is concluded that COMAC factors may detect the changes in frame damage. This index is rather able to detect, locate or quantify damage and effectiveness of retrofitting.
Description: Ph.D.
Appears in Collections:Doctoral Theses@CED

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