Proceedings of the 6 th Asia-Pacific Structural Engineering and Construction Conference (APSEC 2006), 5 – 6 September 2006, Kuala Lumpur, Malaysia A-223 ULTIMATE STRENGTH PREDICTION OF DRM TIMBER BEAMS BY PLASTIC APPROACH: EXPERIMENTAL RESULTS AND DISCUSSIONS Abd. Latif Saleh 1 , Suhaimi Abu Bakar 1 , Zainai B. Mohamed 2 , Khin Maung Zaw 1 1 Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia. 2 Faculty of Civil Engineering, Kolej Universiti Teknologi Tun Hussein Onn, 86400 Parit Raja, Batu Pahat, Johor, Malaysia. E-mail: latif@fka.utm.my ABSTRACT: A new stress model is developed to predict the ultimate bending strength of solid timber beams by using the principle of plasticity. The model predicts the actual bending strength of timber beams from the ratio of ultimate tensile and compressive strengths of the beam material. Standard bending, tension and compression tests are conducted on structural sized specimens to verify the proposed stress model using a local hardwood timber, Dark Red Meranti (DRM). The experimental results of 12 beams, 10 tension specimens and 15 compression specimens are used to verify the proposed model. Test results showed that there is a significant non-linear relationship of the load and the deformation for timber in bending and in compression, but the stress-strain relationship is linear in tension. The strain is linearly distributed across the beam section throughout the test, and the neutral axis shifts towards the tension side when the beam is loaded beyond the proportional limit. Although the tensile strength of timber is larger than its compressive strength, modulus of elasticity (MOE) in tension and compression is approximately the same. Keywords: Timber beams, Ultimate strength prediction, Mathematical stress model, Bending tests, Tension and Compression tests 1.0 INTRODUCTION During the research, bending, tension and compression tests were conducted on structural sized Dark Red Meranti (DRM) timber specimens in accordance with ASTM standard procedures (D 198-84, 1992). A new stress model was also proposed to predict the ultimate bending strength of DRM timber beams. Then, the model was verified by using the experimental results of bending, tension and compression tests. Ultimate tensile and compressive strengths of test specimens were the input parameters in the model. During bending tests, the distribution of strain in mid-section wood fibres, the ultimate load, and the deflection of beams were recorded. The ultimate load and the values of strains at certain load levels were recorded during direct tension and compression tests. Moisture content and density of test specimens were also determined according to ASTM D 4442-92 (1992) and D 2395-83 (1992) procedures. 2.0 SELECTION AND PREPARATION OF TEST SPECIMENS DRM is one of the most commonly used tropical hardwood timbers in Malaysia. It is classified as a light hardwood with an average density of 730 kg/m 3 and specific gravity of 0.47 at 19% moisture content (Choo & Lim, 1983). According to the Malaysian Standard MS 544: Part 2: (2001), it is under the strength group S.G. 5 and the mean value of modulus of elasticity (MOE) is 11200 MPa at moisture content ≤ 19%. Standard structural grade stresses