Performance of Glue Laminated Bamboo Beams and Trusses

Abstract

Bamboo has been known to possess superior strength properties especially its tensile strength that compares well with that of mild steel, has positive environmental impacts of absorbing carbon dioxide and releasing oxygen and matures very fast in 3 to 4 years. However despite these advantages bamboo is not being used widely in construction one limitation being its natural occurrence in cylindrical and hollow form. This research evaluates the performance of glue laminated bamboo beams. Anatomical features of bamboo internode and earlier studies that have shown that, strength properties of bamboo increase from inner to outer layer of the culm and so is the concentration of the cellulose fibers. Mature Bamboo of three and a half years was harvested, split, treated and dried for the study. Tensile test was carried out on strips with nodes, strips with outer skin removed and strips with outer skin intact. Laminated bamboo beams were made in various variations; two orientations, strips facing each other and strips facing same direction in respect to inner and outer face of culm, beams with coinciding nodes at the midpoint, beams made with jointed strips, beams with separated inner and outer parts of the culm, beams with different glue types and a Lattice truss model. Bending, shear and compression tests were performed on the specimens and the lattice truss model was also tested. The results obtained show that orientation of bamboo strips and direction of loading has an effect on flexural strength of laminated bamboo beams, loading on the edge increased the strength by about 20%. Results also show that nodes have a reducing xx i effect on longitudinal tensile strength but have reinforced effect increasing flexural strength of beams, jointed beams have a lower flexural strength but compares well with commonly used timber, type of glue and dispersal affects the strength. In general laminated bamboo beams specimens portrayed superior structural strength properties with a higher MOR of 98 N/mm2 than cypress timber with MOR of 83 N/mm2. The lattice truss models which employed steel plates and bolted connections, did not fail on the joints but rather on excess deflection and deformation of members without rupture of the bamboo material.