Influence of Shape and Dimensions of Lamina on Shear and Bending Strength of Vertically Glue Laminated Bamboo Beam

AbstractThe strength of the bamboo increases from innner surface layer (endodermis) to outer surface layer (exodermis). The strength of bamboo can be utilized optimally by making glue laminated bamboo beams. The curved bamboo lamina as part of the glue laminated beam may be made by peeling off slightly the outer surface layer that contains high strength of fibers. The lamina thickness is made by disposing inner layer of the bamboo. The bamboo used in this work belongs to the species of Bambusa Dendrocalamus asper (local name: bambu Petung). This research aims to improve the shear and flexural strength of the glue laminated bamboo beams by modifying the shape of the cross section of the lamina (curved) rather than ordinary rectangular shape of the lamina.The dimensions of the cross-section of the lamina were of 7/20mm and 9/20mm. The laminas were preserved by immersing them in a hot water having chemical solution namely “Natrium Tetrabonat or CCB4” with a concentration of 10%. Having dry air the laminas were glued using adhesive type PVAC and were staked under 2.5MPa. The cross section dimensions of the beam specimen in shear and bending were of 70/100-900mm and of 70/100-285mm, and of 750mm and 2700mm long respectively. The simply supported glue laminated beams were tested upon two point loads at a distance of 1/3 the length of the span.The results showed that the glue laminated bamboo beams having curved type of laminas are stronger, more rigid, and more ductile compared to rectangular lamina type. Likewise, the glue laminated bamboo beams having 7mm thick of lamina are stronger, stiffer, and ductile compared to the glue laminated beam with laminas of 9mm thick. The average flexural strength of BBR7 (rectangular, 7mm thick of lamina), BBR9 (rectangular, 9mm thick of lamina), BBC7 (curved, 7mm thick of lamina) and BBC9 (curved, 9mm thick of lamina) are respectively (68.80, 9.28, 63.28, 2.00) N/mm2. The flexural rigidity of related beams are respectively (68.36, 71.05, 75.06, 65.17) N/mm, and the ductility are respectively (2.35, 2.16, 1.87, 2.63). The related average shear strength of SBR7, SBR9, SBC7 and SBC9 are respectively (2.72, 2.61, 2.32, 2.64) N/mm2, while the shear rigidity are respectively (2,737.08, 3,029.77, 3,123.87, 2,794.82) N/mm