A new approach to strengthen a glulam beam was investigated. In this study, glulam beams were strengthened by inserting compressed wood blocks into the pre-cut rectangular holes on the top of the glulam beams. This practice was to make use of moisture-dependent swelling nature of compressed wood.In this research, Japanese cedar (Crytomeria japonica D Don) wood was used to manufacture compressed wood blocks and glulam with the initial density of 300-420 kg/m3 and MC of 12% in a dry air condition. The density of the compressed wood was 1163 kg/m3 in average which was increased from 394 kg/m3 of the soft wood. In term of material properties of CW with CR=70%, the Young's Modulus in L,R,T direction increase significantly i.e. EL and Er increase to 32858 MPa and 3111 MPa respectively in comparison with normal Japanese cedar (EL=8017 MPa and ER=753 MPa). Based on the grading data from the Fast Fourier Transform (FFT) Analyzer CF-1200 (produced by Ono Sokki, Japan) with hammering test, the averaged dynamic Young's modulus of lamina for making glulam was 8.44 MPa. The final grades of glulam were varied between 7.96 and 9.81 MPa.Since there is the largest swelling in the radial direction of compressed wood, the CW block was placed in a way in which its radial direction was coincident with the longitudinal direction of the beam to be strengthened.The CW blocks were conditioned to have 6% MC prior to the insertion. Universal testing machine (Instron 1125 with capacity 50 kN) was used to insert CW blocks into pre-cut holes. Once the CW blocks were inserted, they would be gradually swelled by absorbing moisture from air until they reached to the equilibrium state.To measure the pre-camber and initial strain state, all beams were put in chamber with Relative Humidity (RH) fluctuated between 40% until 80% and a constant temperature of 20 °C until the maximum swelling of the CW block was reached. The beams were subjected to measurements of the pre-camber deflection and strains at selected positions of the beam. Readings of transducers and strain gauges were recorded by a personal computer through a data logger where the time interval to record measurements was 30 minutes for about 8/2 weeks.The test results showed that a pre-camber was produced in the mid-span of the beam reinforced. At both the top and the bottom extreme fibres of the beam significant initial tensile and compressive stresses were generated respectively.
展开▼
