Study On The Mechanical Behavior Of Timber Beams Strengthened With Carbon Fiber Reinforced Plastics

Timber structure is the main form of Chinese ancient buildings and famous for its high historical, artistic and scientific value. However, many timber structures have been severely damaged by wind and rain for hundreds or thousands of years. Thus, the reinforcement of the traditional ancient buildings is extremely urgent in present. In recent years, the Carbon Fiber Reinforced Plastic/Polymer (CFRP) sheets have been widely used to strengthen timber structures for the convenience in construction and no influence on the weight and appearance of structures. Therefore, the mechanical behavior of reinforced timber beams using CFRP sheets is studied in this dissertation.An experimental program was conducted to test the flexural beaviour of rectangular timber beams strengthened by CFRP sheets considering the initial load and the number of CFRP layers. The flexural behaviour was examined in terms of the characteristics of failure, the load-deflection relationship, the strain distribution on the cross section of timber beams and the ultimate bearing capacity. The test results indicate that the ultimate load bearing capacity is greatly enhanced and the behavior of deformation of the strengthened timber beams improved.Based on the experimental results, an analytical model was proposed to predict the flexural capacity of the plain timber beams and the reinforced timber beams. The formula of flexural capacity was established considering an initial load according to different models of failure. The calculation results show a good agreement with the experimental results. The experimental and theoretical results indicate that the initial load has significant influence on the stiffness and the deflection of the strengthened beams.A C language program was developed for the nonlinear analysis of the timber beams with externally bonded CFRP sheets considering initial loads. The load-deflection relationship can be drawn out. The predictions of the program agree closely with the test data, which can be used in engineering practice.An analytical model of interfacial stress was proposed for the CFRP-strengthened beams based on the shear-slip deformation of the adhesive layer. The formula for calculating shear stress and normal stress in the interfacial bond between the CFRP sheet and the timber beam were deduced, which were applied to analyze the main factors influencing the maximum interfacial bond stress. Based on the experimental study on the shear property of timber beams strengthened with CFRP sheets, the pattern of shearing failure, the cross section strain and the shear capacity were obtained. The mechanism of two main kinds of shearing failure models were analyzed. The formula of shear capacity were proposed for different failure models. The pattern of strengthening shearing performance of timber beams with CFRP was proposed.