Optimasi Bentuk Struktur Elemen Cangkang Pada Pondasi Terapung Menggunakan Metode Algoritma Genetik
Shape Optimization of Structural Shell Element in Floating Foundation Using Genetic Algorithm Method
DOI:
https://doi.org/10.25299/saintis.2018.vol18(2).2130Keywords:
Struktur Cangkang, Teori Reissner-Mindlin, Algoritma GenetikAbstract
[ID] Prinsip dasar pondasi terapung adalah keseimbangan antara berat struktur atas dan total berat tanah (termasuk didalamnya air tanah) yang dipindahkan oleh konstruksi pondasi tersebut sehingga tidak menghasilkan penurunan struktur. Pondasi terapung sangat baik digunakan pada daerah dengan daya dukung tanah yang rendah atau pada daerah yang memiliki tanah dengan derajat pemadatan yang bervariasi. Hal ini dikarenakan karakteristik pondasi terapung yang membagi gaya ke area kontak yang sangat besar sehingga seluruh area kontak tersebut hanya mengalami tegangan yang relatif kecil. Namun demikian, karena kapasitas dukung pondasi terapung sangat tergantung pada luasan area, maka pondasi terapung menjadi tidak efektif untuk diterapkan pada daerah yang kecil. Salah satu solusi yang dapat digunakan untuk mengatasi permasalahan ini adalah dengan penerapan struktur pelat cangkang (shell structure) pada pondasi terapung untuk meningkatkan luas area bidang kontak pondasi terapung dan tanah. Paper ini membahas optimasi bentuk pelat cangkang yang digunakan pada pondasi terapung agar memiliki daya dukung yang cukup untuk menahan gaya yang ditransferkan oleh struktur atas. Metode algoritma genetik digunakan dalam proses optimasi dimana koordinat dari titik yang menyusun bentuk (shape) struktur cangkang (cn) dipakai sebagai desain variabel. Pada penelitian ini, proses optimasi menggunakan pemodelan dengan 11, 13 dan 15 variabel desain untuk melihat sensitivitas desain variable tersebut terhadap hasil optimasi. Tegangan yang terjadi pada struktur cangkang tersebut di evaluasi dengan Analisa Elemen Hingga dengan perilaku element cangkang seperti model teory pelat Reissner-Midlin. Fungsi tujuan pada penelitian ini adalah meminimalkan penggunaan material untuk membentuk sebuah pondasi terapung dengan fungsi penalti tegangan pada elemen cangkang.
[EN] The basic principle of floating foundation is counterforce balancing between the weight of the structure and thetotal weight of the soil (including groundwater) which is displaced by the structure. Floating foundation is effective in areas with low soil bearing capacity because the external load is widely spread that resulting lower stress level in contact area; Hence, it is necessary to design the shape of floating structure that provide adequate uplift whilst also create lower stress level by spreading the external load to wider contact area. This paper discusses the shape optimization of the floating foundations to have sufficient capacity to resist the force transferred by the upper structure whilst also minimize the use of material without resulting element overstress. Genetic algorithm method is used in the optimization process where the coordinates of the points that shape the shell structure (cn) are used as variable designs. In this study, the multivariable optimization using finite element model is investigated . The stress that occurs in the shell structure is evaluated by Finite Element Analysis with the behavior of shell elements based on Reissner-Mindlin plate theory.
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