Analisis non-linier elemen hingga struktur balok beton prategang dua bentangan
AL FARIDI, Salahuddin, Dr.-Ing. Ir. Djoko Sulistyo
2010 | Tesis | S2 Teknik Sipil-UGMStruktur balok beton prategang dua bentangan umumnya tidak akan mengalami keruntuhan ketika kapasitas momen ultimitnya baru tercapai pada satu penampang kritis saja. Sebuah sendi plastis akan terbentuk pada penampang tersebut sehingga terjadi rotasi yang besar dan beban tambahan seakan-akan dilimpahkan ke lokasi lain sepanjang bentang yang belum mencapai kapasitasnya. Selain secara eksperimental, penelitian dapat juga dilakukan secara numerik dengan analisis non-linier elemen hingga. Penelitian ini bertujuan untuk mengetahui perilaku lentur struktur balok beton prategang dua bentangan berdasarkan analisis non-linier elemen hingga. Pada penelitian ini dibuat 9 model numerik balok beton prategang dua bentangan, yang terdiri dari 3 model balok eksperimen (BC1, BC2, BC3) dengan ukuran penampang 150 mm x 300 mm dan panjang tiap bentang 3000 mm, 3 model balok persegi (BP-R0, BP-R1, BP-R2) dan 3 model balok T (BT-R0, BT-R1, BT-R2). Balok persegi dan balok T masing-masing dengan ukuran penampang dan panjang bentang yang sama, tetapi bervariasi pada tulangan tarik tumpuan tengah. Model numerik balok eksperimen dianalisis dengan program ANSYS dan ATENA, dan hasilnya dibandingkan dengan hasil eksperimen yang dilakukan oleh Bishara dan Brar (1974) dalam Rebentros (2003). Setelah diperoleh validasi, dilakukan analisis balok yang sama namun dengan variasi mutu beton dan nilai As,sup/As,mid. Selanjutnya dilakukan analisis model numerik balok persegi dan balok T untuk melihat hubungan beban-lendutan, kekakuan, daktilitas, pola retak, hubungan beban-momen, dan redistribusi momen. Hasil penelitian menunjukkan bahwa struktur balok beton prategang dua bentangan dapat dimodelkan dengan baik menggunakan ANSYS dan ATENA. Untuk balok BC1, BC2 dan BC3, perbedaan beban ultimit antara hasil analisis ANSYS dan hasil eksperimen oleh Bishara dan Brar berturut-turut sebesar 0,51%, 1,04% dan 0%, dan untuk ATENA sebesar 2,56%, 0,52% dan 0,52%, Perbedaan kekakuan antara hasil analisis ANSYS dan hasil eksperimen sebesar 146,11%, 54,23% dan 18,52%, dan untuk ATENA sebesar 188,61%, 81,95% dan 40,17%. Perbedaan daktilitas antara hasil analisis ANSYS dan hasil eksperimen sebesar 143,97%, 24% dan 25,06%, dan untuk ATENA sebesar 154,72%, 58,66% dan 12,02%. Beban ultimit balok persegi dan balok T hasil analisis ANSYS lebih besar dari ATENA, berturut-turut untuk BP-R0, BP-R1, BP-R2, BT-R0, BT-R1 dan BT-R2 sebesar 5,37%, 5,95%, 6,59%, 3,06%, 3,09% dan 4,17%. Kekakuan hasil analisis ANSYS lebih kecil dari ATENA sebesar 3,36%, 3,44%, 3,51%, 12,34%, 11,5% dan 11,51%, dan daktilitasnya juga lebih kecil dari ATENA sebesar 18,55%, 30,38%, 27,15%, 5,35%, 7,04% dan 8,15%. Pola retak pada seluruh model menunjukkan terjadinya kegagalan lentur. Nilai redistribusi momen sangat dipengaruhi nilai As,sup/As,mid, dimana redistribusi momen akan meningkat dengan pengurangan As,sup/As,mid.
Two-span prestressed concrete beams normally will not fail when the moment capacity of just one critical section is reached. A plastic hinge will form at that section, permitting large rotation to occur and thus transferring load to other locations along the span where the moment capacity has not yet been reached. Beside experimental, research can be held by using non-linear finite element analysis. This research was conducted to study the flexural behavior of two-span prestressed concrete beams based on non-linear finite element analysis. In this research nine numerical models of two-span prestressed concrete beams were made and consist of: 1) three experimental beams (BC1, BC2, BC3) with cross sectional dimension of 150 mm x 300 mm and 3000 mm long each span as referred by Bishara and Brar (1974) as quoted by Rebentros (2003); 2) three rectangular beams (BP-R0, BP-R1, BP-R2); and 3) three tee beams (BT-R0, BT-R1, BT-R2). Each rectangular and tee beams were of equal cross section and span length but vary in tensile reinforcement at interior support. Numerical models of the experimental beams were analyzed by non-linear finite element method using ANSYS and ATENA software. Result of the analysis was calibrated against experimental results from Bishara and Brar (1974) in Rebentros (2003). Once validated, the models were re-analyzed with the variation of concrete strength and As,mid/As,sup. Further, numerical models of rectangular and tee beams were analyzed to examine the load-deflection relationship, stiffness, ductility, crack pattern, load-moment relationship and moment redistribution. Result of the research shows that two-span prestressed concrete beams can be well modeled using ANSYS and ATENA. The differences of ultimate load strength between ANSYS and experimental result by Bishara and Brar for BC1, BC2 and BC3 were 0.51%, 1.04% and 0%, and for ATENA were 2.56%, 0.52% and 0.52%. The differences of stiffness between ANSYS and experimental result were 146.11%, 54.23% and 18.52%, and for ATENA were 188.61%, 81.95% and 40.17%. The differences of ductility between ANSYS and experimental result were 143.97%, 24% and 25.06%, and for ATENA were 154.72%, 58.66% and 12.02%. The ultimate load strength of ANSYS for rectangular and tee beams were greater than ATENA, for BP-R0, BP-R1, BP-R2, BT-R0, BT-R1 and BT-R2 were 5.37%, 5.95%, 6.59%, 3.06%, 3.09% and 4.17% respectively. The stiffness of ANSYS were smaller 3.36%, 3.44%, 3.51%, 12.34%, 11.5% and 11.51% than ATENA. The ductility of ANSYS were smaller 18.55%, 30.38%, 27.15%, 5.35%, 7.04% and 8.15% than ATENA. Crack pattern for all beams shows that the beams fail in flexure. The load-moment relationship shows that moment redistribution begins after the formation of the first crack. The value of moment redistribution were highly influenced by As,sup/As,mid. Moment redistribution increases with the decrease of As,sup/As,mid.
Kata Kunci : Struktur balok beton prategang dua bentangan,Analisis non,linier elemen hingga,ANSYS,ATENA,redistribusi momen, two-span prestressed concrete beam, non-linear finite element analysis, ANSYS, ATENA, moment redistribution
