PENGUJIAN MODEL PIPA PESAT KAYU PADA KONDISI KERING UDARA DAN JENUH AIR

Anita Hayuniati, Ali Awaludin, S.T., M.Eng., Ph.D.

2012 | Tesis | S2 Teknik Sipil

Pipa pesat kayu dalam penelitian ini berfungsi untuk membawa air yang bertekanan untuk menggerakkan PaT (Pumps Used as Turbines) yang mengangkat aliran air dari aliran sungai di bawah permukaan tanah ke permukaan di gua Seropan, Gunungkidul Yogyakarta. Pengujian model pipa pesat dari kayu Durian ini dilakukan dengan pembebanan berupa tekanan dari dalam (internal pressure) secara bertahap sampai mencapai 2,7 bar baik pada kondisi kering udara maupun jenuh air. Pengamatan displacement dilakukan dengan LVDT pada posisi atas, samping kanan, kiri dan bawah pipa pesat kayu. Pengamatan juga dilakukan pada tegangan kayu arah longitudinal dan tangensial serta tegangan pada cincin besi pengaku. Selain itu, pemeriksaan sifat fisika kayu meliputi kadar air dan kerapatan serta sifat mekanika kayu berupa pengujian lentur dan tekan tegak lurus serat dilakukan juga pada beberapa jenis kayu sebagai alternatif bahan pembuatan pipa pesat selain kayu Durian. Hasil pengujian ekperimental kemudian dibandingkan dengan nilai pemanfaatan design pipa pesat kayu di gua Seropan yang disarankan dari hasil penelitian Karlsruhe Institute of Technology (KIT), Jerman dari model elemen hingga. Hasil pengujian kondisi jenuh air pada internal pressure sebesar 2,7 bar dan jarak antar cincin pengaku 40 cm ditambah tegangan akibat swelling menunjukkan displacement radial tertinggi yang terjadi sebesar 5,4 mm, tegangan longitudinal kayu tertinggi sebesar σL = 11,590 MPa (65,87% MORr), tegangan tangensial kayu tertinggi sebesar σ = 4,597 MPa (48,01% fc,90,r) dan tegangan cincin besi tertinggi yang terjadi sebesar 132,871 MPa (44,29% σy). Kayu Durian dari hasil pengujian diperoleh kuat lentur sebesar 20,7 MPa dan kuat tekan tegak lurus serat sebesar pada strain 10% sebesar 14,17 MPa. Hasil penelitian KIT pada model elemen hingga, nilai pemanfaatan tegangan kayu yang disarankan sebesar 48% sedangkan gaya aksial pada cincin besi sebesar 60%. Hasil pengujian pipa pesat kayu Durian menunjukkan tegangan yang terjadi dari hasil eksperimen mendekati hasil dari model elemen hingga. Kayu Durian termasuk kelas kuat C20 (kuat lentur 20 MPa) sedangkan kuat kayu yang disarankan merupakan kelas kuat C24 (kuat lentur 24 MPa). Dengan demikian kayu Durian dapat digunakan sebagai bahan pipa pesat kayu.

Wood stave pipeline in this study was used to bring prezurized water to generate PaT (Pumps Used as Turbines) for lifting the water flow from underground river to the surface in Seropan Cave, Gunungkidul Yogyakarta. This experimental study of wood stave pipeline made from Durian wood was carried out through loading of internal pressure gradually in phases up to reach 2,7 bar under dry and water saturated conditions. The observation of displacement was taken by using LVDT at above, left and right, and under positions of the wood stave. The observation was also carried out to the wooden stress at longitudinal and tangential directions as well as the stress on the ring stiffener. Some physical and mechanical properties of several wood species, used as the alternative wood stave material other than Durian wood, were also inspected. The inspection of physical properties included the moisture content and density. The inspection of mechanical properties included the tests of bending strength and compressive perpendicular to grain. Results of the test were then compared to the utilization value of the wood stave design in Seropan Cave, as recommended in the results of the research carried out by Karlsruhe Institute of Technology (KIT), Germany for the finite element models. The test results at 2,7 bar internal pressure under water saturated condition and 40 cm ring stiffener distance and added with swelling stress indicated that the highest radial displacement, wood longitudinal stress, wood tangential stress and ring stiffener stress were 5,4 mm, σL = 11,590 MPa (65,87% MORr), σT = 4,559 MPa (48,01% fc,90,r) and 132,871 MPa (44,29% σy), respectively. Durian wood, based on the study, showed that the bending strength and compressive strength perpendicular to grain at 10% strain were 20,7 MPa and 14,17 MPa, respectively. Results of KIT research on the finite element model recommended that the value of wood stress utilization and axial force were 48% and 60%, respectively. The test results on Durian wood stave pipe indicated that the stress, based on the experiment, was close to the finite element model. Durian wood was categorized in strength class C20 (bending strength 20 MPa) where as the recommended wood strength is in strength class C24 (24 MPa bending strength). It can be concluded that Durian wood can be used as the material for wood stave pipeline.

Kata Kunci : Gua Seropan, pipa pesat kayu, sifat fisika dan mekanika kayu