Experiments and analysis on the novel technique for RC members retrofitted by carbon fiber reinforced polymers

• Main Authors: Ying-Han Wu, 吳穎涵
• Other Authors: Chih-Tsung Lin
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/tqxjxk

博士 === 國立臺北科技大學 === 工程科技研究所 === 101 === In this paper, two subjects were studied. For the first one, the novel retrofit technique-CFRP Anchor was presented to improve the retrofit performances for RC structures. The testing bond performance and design theorems were discussed and tested in practical experiments with a total of forty six specimens. Test programs for the fiber bolt and spread tails, the components of CFRP anchors, were carried out under tensile loading. To access the applicability for the technique, the rectangular RC column retrofitted by using CFRP combined with CFRP anchors was presented to improve the seismic performances. Seven full-scale RC columns in two series were constructed with low transverse reinforcement ratios and tested under lateral cyclic loadings with a constant axial load. Experimental results showed that the benchmark specimen, which was not retrofitted, was shear failure. The proposed technique avoids the occurrence of the premature CFRP breakage on corner zones and provides confinement on column faces as the comparison to tests using CFRP alone. The use of CFRP anchors significantly improved the behavior of CFRP wrapping on rectangular columns, such as increased the ductility and the energy dissipation. In addition, a flexural strengthening system of longitudinal CFRP bonded with CFRP anchors doweling into column footings was tested and verified. Moreover, a total of eleven rectangular RC columns with low transverse reinforcement ratio were constructed to test the confining performance using different retrofit schemes including the proposed CFRP combined with CFRP anchor technique. Among them, one was tested as benchmark; one was purposely constructed with larger transverse reinforcement ratio; five were retrofitted by using CFRP wrapping combined with CFRP anchors; and the other four were retrofitted by using different shapes of steel jacketing alone or with adhesive anchors. All the specimens were subjected to monotonic incremental axial force until failure occurred. Experimental results demonstrated that the compression ductility of the specimens retrofitted by CFRP anchors was significantly improved compared with those retrofitted by using only CFRP wrapping alone. On the other hand, the specimen with octagonal steel jacketing performed better than all other specimens not only on ductility but also on strength. An model considering the contribution of the retrofit material was proposed and validated in the numerical analysis. The second subject in this paper is the effects of fatigue leading to crack formation and potential durability-bonding problems in reinforced concrete (RC) beams strengthened by CFRP. These effects are shown to cause CFRP debonding and loss of load carrying capabilities under static or low cyclic loading. Two series of RC beams with CFRP strengthening system are constructed and designed to fail in shear and flexural failures, respectively, under static loading. Repeated loading tests are conducted according to various loading ranges and loading cycles, and the experimentally determined fatigue properties are discussed. The test result show that it is possible to eliminate the debonding modes for longitudinally bonded CFRP using U-wrap CFRP combination. The fatigue loads tested a significant effect on concrete rather than the CFRP system especially for the strengthened beams bearing a higher shear level. Moreover, the equation to fit the testing S–N curve and the discussion of the stress in the component materials could be used for fatigue life predictions of beams with CFRP strengthening systems.