Strength Ratio Empat Jenis Kayu Berdasarkan Kandungan Cacatnya

Abstract

Cacat-cacat kayu dapat mereduksi kekuatannya, sehingga kekuatan kayu bervariasi akibat kandungan cacat tersebut. Penelitian ini bertujuan melihat reduksi kekuatan kayu Pinus (Pinus merkusii), Meranti merah (Shorea leprosula), Jabon (Anthocephalus cadamba), dan karet (Hevea brasiliensis) akibat adanya cacat berdasarkan nilai strength ratio (SR). Penelitian ini mengacu pada ASTM D-245 dengan parameter uji berupa mata kayu dan kemiringan serat. Untuk mengetahui nilai strength ratio akibat mata kayu dibutuhkan informasi berupa diameter mata kayu (mm), tebal/lebar kayu (mm) dan letak mata kayu (narrow face/wide face). Kemiringan serat (slope of grain) dapat diperoleh dengan cara menarik garis tegak lurus yang dinyatakan sebagai tinggi dan alas kemudian dilakukan perhitungan menggunakan rumus tangen. Evaluasi strength ratio akhir dilakukan berdasarkan perhitungan nilai minimum strength ratio akibat mata kayu dan miring serat berdasarkan tipe tegangan yang dihasilkan. Evaluasi quality factor MOE didapatkan berdasarkan nilai strength ratio akhir. Hasil penelitian menunjukkan bahwa diameter mata kayu terbesar terdapat pada jenis meranti merah, sedangkan jumlah mata kayu terbanyak terdapat pada jenis pinus. Hasil pengamatan membuktikan bahwa terdapat mata kayu terikat (tight knots) pada jenis pinus dan karet, sedangkan pada jenis jabon dan meranti merah terdapat mata kayu longgar (loose knots). Nilai strength ratio akibat miring serat pada kayu jabon lebih kecil dibandingkan kayu meranti merah. Rendahnya nilai strength ratio akhir pada kayu jabon mengakibatkan kayu jabon tidak dianjurkan dalam kontruksi berat. Nilai MOE kayu bercacat dapat diperoleh dari hasil pengujian ASTM D-143 dikalikan dengan quality factor, yang tertera pada tabel standard ASTM D-245.

It is well-known that wood defects may reduce the woods’ strength, than their strength may vary dependent on the amount of defects. This study aimed to assess the strength reduction of pine wood (Pinus merkusii), red meranti wood (Shorea leprosula), Jabon wood (Anthochephalus cadamba) and rubber wood (Hevea brasiliensis) due to defects as indicated by the strength ratio. This work referred the ASTM D-245 standard within test parameters of knots and slope of grains. In order to obtain the value of the strength ratio due to knots, it requires the data of the knots diameter (mm), thickness/width of wood and also the location of knots (narrow face/wide face). The slope of grain was determined by drawing a perpendicular line to the grains using a very simple tangent formula. The final strength ratio was determined using both the minimum strength ratio due to knots and the slope of grains; considering the the type of stress produced. Evaluation of quality factor MOE is obtained based on the final strength ratio value as provided in the table of ASTM D-245 standard. The results showed that the largest knots diameter was found in the red meranti woods, while the highest number of knots was found in the pine woods. Also, this study observed that there are tight knots found within the pine and the rubber woods. Meanwhile, the jabon and the red meranti woods have loose knots. The value of the strength ratio due to the slope of grain in jabon wood is far too smaller than the red meranti wood. Moreover, the final strength ratio in jabon wood was found to be very low. As a consequence, the jabon wood was not recommended to be used for heavy contructions. The MOE value of defective wood can be obtained using the ASTM D-143 test results, and multiplied by the quality factor that provided in the ASTM D-245 standard table.