Effectiveness of repair method using hybrid fiber reinforced polymer fabric on concrete-filled double skin steel tubular columns exposed to fire / Sharifah Salwa Mohd Zuki
Tiang keluli dwi lapisan berisi konkrit (CFDST) menjadi semakin popular pada masa kini di sebabkan oleh prestasinya yang tinggi berbanding dengan tiang komposit konvensional dan tiang keluli berisi konkrit (CFST). Walau bagaimanapun, penggunaan tiang jenis ini terhad kepada pembinaan luar seperti jambatan dan menara penghantaran (transmission tower) di mana api bukan merupakan satu kebimbangan utama. Tambahan pula, kajian sedia ada mengenai tiang CFDST hanya memberi tumpuan kepada prestasi tiang terhadap api dan kajian mengenai kekuatan sisa tiang CFDST pasca-kebakaran adalah terhad. Kekuatan sisa boleh digunakan untuk menentukan kaedah pembaikan yang paling sesuai supaya tiang tersebut kembali berfungsi seperti sediakala. Oleh itu, kajian ini bertujuan untuk mengkaji kesan parameter yang berbeza terhadap kekuatan sisa tiang CFDST. Antara parameter yang di bincangkan ialah ketebalan tiub keluli luar dan masa pendedahan kepada api. Kajian ini juga menilai keberkesanan kaedah pembaikan menggunakan polimer gentian (FRP) tunggal dan Hibrid terhadap prestasi tiang CFDST yang rosak akibat api. Tiang CFDST dibakar mengikut ASTM E119-11: Standard Test Methods for Fire Tests of Building Construction and Materials sehingga mencapai suhu 600°C. Selepas itu, suhu dimalarkan untuk dua jangka masa yang berbeza, iaitu, 60 minit dan 90 minit. Spesimen itu kemudian dibiarkan menyejuk pada suhu bilik di dalam relau sebelum ia dibawa keluar dan dibaiki sama ada dengan menggunakan FRP tunggal atau Hibrid. Spesimen dikategorikan kepada 3 kumpulan iaitu (1) spesimen tidak dibakar atau kawalan, (2) dibakar dan tidak dibaiki dan (3) dibakar dan dibaiki. Semua spesimen dibebankan dengan beban mampatan paksi sehingga gagal. Kategori pertama dan kedua spesimen gagal disebabkan oleh lengkokan tempatan ke arah luar daripada tiub keluli luar, kehancuran konkrit dan lengkokan tempatan daripada tiub keluli dalaman; manakala, spesimen daripada kategori ketiga gagal disebabkan oleh kegagalan FRP diikuti oleh lengkokan tempatan dan kehancuran konkrit seperti kategori pertama dan kedua. Kekuatan, kekukuhan sekan dan Indeks Kemuluran (DI) berkurang apabila suhu specimen meningkat. RSI dan kekukuhan Sekan meningkat apabila masa pendedahan meningkat. Menariknya, RSI tertinggi yang dicapai hanya 22% yang bermaksud, spesimen masih mampu membawa lebih daripada 70% daripada beban asal selepas terdedah kepada api selama 90 minit dengan hanya 3 mm ketebalan tiub keluli luar. Pembaikan tiang CFDST yang rosak akibat api dengan menggunakan FRP tunggal dan Hibrid berjaya menambahkan kekuatan muktamad tiang. Peningkatan kekuatan muktamad adalah lebih ketara apabila spesimen dibaiki dengan kaedah Hubrid FRP bersama spesimen yang mempunyai ketebalan tiub keluli luar yang nipis. Walau bagaimanapun, kenaikan dalam Kekukuhan Sekan dan Indeks Kemuluran (DI) spesimen yang dibaiki tidak mencapai nilai asal.
__________________________________________________________________________________
Concrete-filled double skin steel tubular (CFDST) column is becoming more popular nowadays due to its superior performance compared to conventional composite column and concrete-filled steel tubular (CFST) column. However, the use of this type of column is still limited to outdoor construction such as bridge piers and transmission tower where fire is not a main concern. Moreover, existing research studies on CFDST column only focused on fire performance and limited research studies can be found on residual strength of the CFDST column. Residual strength can be used to determine the most suitable repair method needed in order to retrofit the column. Therefore, this study aims to study the effect of different parameter towards residual strength of CFDST column. Among discussed parameter is thickness of outer steel tube ( ) and fire exposure time. In addition, this study is also aim to determine the effectiveness of repair method using Single and Hybrid fiber reinforced polymer (FRP) of fire-damaged CFDST columns. CFDST columns were heated in accordance of ASTM E119-11: Standard Test Methods for Fire Tests of Building Construction and Materials until the temperature reached 600°C. Afterwards, the temperature was kept constant for two different durations, i.e., 60 minutes and 90 minutes. The specimen was then left to cool down to room temperature inside the furnace before it was taken out and repaired by Single and Hybrid FRP. The specimens were categorized into the following three groups: (1) unheated or control specimens, (2) heated and unrepaired and (3) heated and repaired. All specimens were subjected to axial compression loading until failure. The first and second category specimens failed by local outward buckling of outer steel tube, crushing of concrete and local buckling of inner steel tube; whereas, specimens in third category failed by rupture of FRP followed by similar local buckling and concrete crushing as those observed in first and second category specimens. Ultimate strength, secant stiffness and Ductility Index (DI) decreased as temperature of the specimen increased. The lost in secant stiffness of thinner CFDST specimens exposed to 60 minutes of fire exposure time is similar to thicker CFDST specimens exposed to 90 minutes of fire exposure time regardless of its diameter. In addition, CFDST specimens exposed to 90 minutes of fire exposure time were more ductile than control specimen. RSI and secant stiffness increased with the increased in fire exposure time. Interestingly, the highest RSI achieved is only 22% which means the specimens were still able to carry more than 70% of its initial load after being exposed to 90 minutes of fire exposure time with only 3 mm thickness of outer steel tube. Repairing the fire-damaged CFDST columns with Single and Hybrid FRP are proven to improve ultimate compressive strength significantly. The increment in ultimate compressive strength is more pronounced in specimen with Hybrid FRP and thinner outer steel tube. The secant stiffness and Ductility Index (DI) of repaired specimens were however not able to be restored to those of control specimen.
Effectiveness of repair method using hybrid fiber reinforced polymer fabric on concrete-filled double skin steel tubular columns exposed to fire / Sharifah Salwa Mohd Zuki
Effectiveness of repair method using hybrid fiber reinforced polymer fabric on concrete filled double skin steel tubular columns exposed to fire_Sharifah Salwa Mohd Zuki_A9_2017_MYMY