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    Compressive behavior of large-scale square reinforced concrete columns confined with carbon fiber reinforced polymer jackets
    (Elsevier Sci Ltd, 2010) Turgay, Tahsin; Polat, Z.; Köksal, Hasan Orhun; Doran, Bilge; Karakoç, C.
    Several experimental and analytical studies on the confinement effect and failure mechanisms of fiber reinforced polymer (FRP) wrapped columns have been conducted over recent years. Although typical axial members are large-scale square/rectangular reinforced concrete (RC) columns in practice, the majority of such studies have concentrated on the behavior of small-scale circular concrete specimens. The data available for square/rectangular columns are still limited. This paper reports the results of an experimental research program on the performance of large-scale square RC columns wrapped with carbon fiber reinforced polymer (CFRP) sheets. Attention is focused on the investigation of the total effect of longitudinal and transverse reinforcement and FRP jackets on the behavior of concentrically loaded columns. A total of 20 large-scale RC columns were fabricated and tested to failure under axial loading in the structural laboratory. Three types of columns were primarily considered: unwrapped; fully wrapped; and partially wrapped. Based on the test results of RC columns, existing experimental data and procedures in the literature are also evaluated. Furthermore, stress-strain curves of the columns are successfully predicted by the analytical approach previously proposed for FRP-confined concrete. (C) 2009 Elsevier Ltd. All rights reserved.
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    Stress-strain model for concrete confined with CFRP jackets
    (Elsevier Sci Ltd, 2009) Turgay, Tahsin; Köksal, Hasan Orhun; Polat, Z.; Karakoç, C.
    Enhancement of strength and ductility is the main reason for the extensive use of FRP jackets to provide external confinement to reinforced concrete columns especially in seismic areas. Therefore, numerous researches have been carried out in order to provide a better description of the behavior of FRP-confined concrete for practical design purposes. Most of the existing models are based on the improved or modified forms of the well known empirical formula of Richart et al. derived from the tests on concrete cylinders. Compressive strength of concrete is predicted without a failure criterion for this modeling approach. There exist only a few models that employ the simplified or modified forms of five-parameter failure criterion proposed by William-Warnke. This paper primarily concentrates on the modeling of FRP-confined concrete using a practical failure surface based on only unconfined compressive strength of concrete. A large comparative analysis is accomplished for the existing test data of 127 cylindrical concrete specimens confined with CFRP jackets. The performance of five existing analytical models for the prediction of the compressive strength of FRP-confined concrete is evaluated leading to the detection of the proposed approach as the most accurate one through this comparative study. Moreover, the complete stress-strain curves of eight concrete cylinders obtained from four different experimental studies are plotted adopting both the stress-strain relation of Saenz and the predictions for compressive strength of the approach. Comparisons between the experimental and analytical results point out that the proposed approach provides satisfactory predictions for both the compressive strength and the stress-strain plots of CFRP-confined concrete. (C) 2008 Elsevier Ltd. All rights reserved.