Rasuk kekotak, dengan kekuatan kilasan tinggi, ringan dan rintangan struktur yang besar, amat popular digunakan dalam struktur jambatan. Walau bagaimanapun, rasuk kotak mungkin gagal dengan tiba-tiba disebabkan oleh jumlah dan beban trafik meningkat dan kapasiti berkurang akibat dan pada kemerosotan. Teknik pengukuhan polimer bertetulang gentian (FRP) telah dikaji dan digunakan dalam struktur untuk meningkatkan keupayaan lenturan dan ricih rasuk. Namun, sangat sedikit perhatian ditumpukan kepada rasuk kotak konkrit bertetulang (RC) dari segi ricih, kilasan, mahupun gabungan ricih-kilasan. Oleh itu dalam kajian ini, tiga set ujikaji ke atas rasuk kotak RC diperkukuhkan dengan polimer karbon-bertetulang gentian (CFRP) dalam ricih, kilasan tulen, dan gabungan ricih-kilasan telah dijalankan. Berdasarkan eksperimen, matlamat utama adalah untuk: (a) meramal sumbangan ricih CFRP; (b) menilai keberkesanan pengukuhan dan meramalkan sumbangan CFRP kepada kilasan; (c) menyiasat kelakuan rasuk kotak dengan pengukuhan tertakluk kepada gabungan ricih-kilasan dan membangun persamaan matematik untuk meramal kekuatan. Model fib Bulletin 14 dengan koefisien pengurangan yang dicadangkan dalam keberkesanan urat fiber dapat meramalkan sumbangan CFRP dalam ricihan pada rasuk kekotak RC diperkukuhkan. Di samping itu, didapati bahawa konfigurasi CFRP U-jacketing dengan jalur membujur mempunyai prestasi yang lebih baik dalam pengukuhan kilasan RC kotak rasuk. Satu model penggabungkan telah didedahkan sebagai model yang boleh dipercayai dan konservatif dalam menghitung kekuatan kilasan rasuk RC dipasang. Seterusnya, keberkesanan pengukuhkan CFRP dalam gabungan ricih-kilasan RC rasuk kotak adalah berkadar songsang dengan nisbah kilasan-ricih. Persamaan yang diperoleh dengan model ubahsuai ketegangan berkesan dalam serat dapat memberi keputusan wajar ke atas kekuatan kilasan kepada rasuk kotak RC dengan pengukuhan atau tanpa pengukuhan tertakluk kepada tindakan gabungan.
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Box beams, with high torsional stiffness, light weight, and great structural resistance, are popularly used in the bridge structures. However, these box beams may fail suddenly due to increased traffic volumes and loads and diminished capacity from deterioration. Fiber-reinforced polymer (FRP) strengthening technique has been studied and used in structures to improve the flexural and shear capacity of beams. However, very few strengthening studies have paid much attention to reinforced concrete (RC) box beams subjected to shear, torsion, and combined shear and torsion. Therefore, in this research, three sets of experiments on RC box beams strengthened with the carbon-fiber-reinforced polymer (CFRP) in shear, pure torsion, and combined shear and torsion were conducted. Based on experiments, the main aims are to: (a) predict the shear contribution of CFRP; (b) evaluate the strengthening effectiveness and predict the CFRP contribution to torsion; (c) investigate the behavior of strengthened box beams subjected combined shear and torsion and develop mathematical equations to predict strength. The fib Bulletin 14 model with the reduction coefficient proposed in effective strain of fiber could reliably predict the shear CFRP contribution to shear in strengthened RC box beam. In addition, it was found that the configuration of CFRP U-jacketing with longitudinal strips had a better performance in the torsional strengthening of RC box beam. One combined model had been revealed to be reliable and conservative in calculating the torsional strength of retrofitted RC beams. Further on, strengthening effectiveness of CFRP in combined shear and torsion to RC box beams was inversely proportional to torque-to-shear ratio. The derived equations with modified model of effective strain in fiber could give the desirable results of torsional strength to the strengthened or unstrengthened RC box beams subjected combined action.
Reinforced concrete box beam strengthened by carbon-fiber-reinforced polymer subjected to combined shear and torsion_Ma Shengqiang_A9_2017_MYMY