Anggota konkrit mengalami kilasan diiringi juga dengan lenturan dan ricihan. Sehingga kini, kod amalan reka bentuk anggota-anggota konkrit bertetulang menganggap bahawa kesan kilasan dapat dielakkan dengan selamat disebabkan faktor keselamatan yang tinggi digunakan dalam lenturan dan ricihan. Justeru itu, gabungan beban terhadap anggota-anggota tidak diberi perhatian yang serius. Namun demikian, andaian ini sudah tidak boleh diaplikasi lagi kerana isu kilasan kini merupakan perkara biasa dan memainkan peranan yang signifikan dalam struktur, contohnya rasuk spandrel. Rasuk
spandrel atau dikenali juga sebagai rasuk-L, amat bergantung pada perimeter bangunan. Sebarang kegagalan pada rasuk spandrel boleh menjadi serius sehingga mencacatkan papak, sumbungan tiang-rasuk dan tebukan plat rata konkrit. Dengan mencampurkan gentian keluli sebagai bahan tambahan, ia boleh meningkatkan kekuatan kilasan rasuk spandrel di bawah beban gabungan dan prestasi struktur konkrit seperti beban maksimum, kemuluran dan rintangan retak. Gentian keluli boleh merintangi gabungan beban seperti rakap dan tetulang membujur, namun penyelidikan di dalam bidang ini masih samar dan terhad. Lebih-lebih lagi kepentingan menggunakan bertetulang gentian dalam struktur konkrit untuk diaplikasi dalam infrastruktur awam telah meningkat. Oleh yang demikian, pengetahuan sedia ada tentang konkrit gentian keluli sepaiknya
digabungjalinkan dalam kod amalan reka bentuk. Eksperimen dijalankan untuk menilai perlakuan rasuk spandrel gentian yang diperkukuh dengan gentian keluli tertakluk pada gabungan kilasan, lenturan dan ricihan. Sejumlah 18 rasuk spandrel disediakan dan diuji dengan dua gabungan beban biasa i.e. kilasan tinggi terhadap nisbah lenturan dan kilasan rendah terhadap nisbah lenturan. Sampel rasuk dibahagikan kepada tiga kumpulan, iaitu rasuk konkrit biasa, spesimen dengan tetulang pengukuh memanjang, dan spesimen dengan tertulang dan rakap. Semua kes dikaji dengan pecahan isipadu
gentian keluli 0%, 1%, dan 1.5%. Rasuk konkrit bertetulang gentian mempamerkan prestasi keseluruhan yang baik berbanding dengan rasuk kawalan tanpa gentian. Diperhatikan sumbangan utama daripada gentian keluli ke atas tingkah laku kilasan adalah terhadap keretakan konkrit. Penambahan gentian keluli adalah penting untuk rasuk tanpa tetulang keluli konvensional, penambahan ini terbukti mampu meningkatkan kapasiti semasa kilasan. Di samping itu, analisis berangka melalui kaedah elemen terhingga dilakukan terhadap data eksperimen untuk meramalkan tingkah laku struktur
rasuk spandrel. Satu teknik baru diutara untuk mengambilkira kesan gentian keluli dalam elemen konkrit dan kesan titik lembut konkrit dalam mampatan dan tegangan. Kelakuan umum model unsur terhingga yang diwakili plot kilas-piuh dan plot bebanlenturan menunjukkan hubungan yang baik dengan data ujian daripada rasuk kawalan dan rasuk spandrel. Walau bagaimanapun, model unsur terhingga menunjukkan kekukuhan yang tinggi berbanding dengan data ujian dalam julat tidak linear untuk rasuk tanpa tetulang keluli.
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Important concrete members are subjected to significant torsion accompanied by bending and shear. Until recent years, the design codes of reinforced concrete members assumed that the effects of torsion could be safely neglected due to high safety factors for shear and bending moment. Thus, members under combined loading were not treated with serious attention. However, this assumption cannot be applied anymore as torsion issues become common and play a significant role in structural members, such as spandrel beams. The spandrel beam, or the L-beam, lies on the perimeter of buildings.
Any failure in spandrel beams can seriously damage slabs, beam-column connections, and punch concrete flat-plates. By incorporating steel fibers, it can enhance torsional behavior of spandrel beam under combined load in addition to the structural performance such as maximum load, ductility and cracking resistance. Steel fibers may provide resistance to combined loading as stirrups and longitudinal bars, this investigation is still scare and limited. Moreover, a worldwide interest in utilizing fiber reinforced concrete structures for civil infrastructure applications has increased. This study presents the advantage of using steel fiber concrete in strengthening spandrel beams under different reinforcement and loading cases. An experimental investigation was conducted to assess the behavior of steel fiber reinforced concrete spandrel beams
subjected to combined torsion, bending, and shear. A total of 18 spandrel beams were prepared and tested with two common loading combinations i.e. high torque to bending ratio and low torque to bending ratio. All beams were divided into three groups, namely, plain concrete beams, specimens with longitudinal reinforcing bars and specimens with bars and stirrups. All cases were examined with 0%, 1%, and 1.5% steel fiber volume fractions. Fibrous concrete beams exhibited improved overall torsional performance with respect to the corresponding non-fibrous control beams. The main contribution of steel fibers on the torsional behavior is mainly observed after concrete cracking. The addition of steel fibers was essential to the beams without conventional steel reinforcement since fibers were the only reinforcement and proved capable to provide enhanced torsional moment capacities. Besides, a numerical analysis by finite element method was suggested against the experimental data to predict the structural behavior of spandrel beams. A new technique was presented to incorporate the effects of steel fibers within concrete element and the softening effect of concrete in compression and tension. The general behavior of the finite element model represented by the torque-twist plot and load-deflection plots show good agreement with the test data from the plain and fiber reinforced spandrel beam. However, the finite element models show higher stiffness than the test data in the nonlinear ranges for beams without steel reinforcement.
Behavior of spandrel beams strengthened with steel fibers under combined loading / Omer Farouk Ibraheem