ABSTRACT
Timber remains one of the most important building materials today, research and technology have produced extensive knowledge about its strength, workability, performance and cost. This helps structural engineers to use timber more effectively in more challenging applications. The most widely used wood construction technology is glue laminated timber. Glue laminated timber is a structural engineered timber product that is made up of multi-dimensional timber bonded with a durable, moisture- proof structural adhesive. This study aims to determine the effect of laminate thickness (3, 4 and 5 laminates) and also assess comparatively the flexural, compressive and tensile strength of some Nigeria timber species in the development of glue laminated timber beams as structural elements in construction.
The materials used for this study include timbers (stress graded according to BS 5268) and polyvinyl acetate glue. Three species of timber were used for this study, they are; Ekki (Lophira Alata), Baphia (Baphia nitida), Apa (Afzelia bipindensis). The physical properties of the timber species including moisture content and density were determined in accordance with BS373;1957. Mechanical properties of the timber species such as bending strength, tensile strength test perpendicular to grain and compression test parallel to grain were determined based on standards such as ASTM D193 (2000), BS373;1957 with dimensions of 10mm x 50mm x 1000mm for flexural strength, 10mm x 50mm x 200mm for compressive strength and tensile strength.
Moisture content was determined in accordance to BS 373: 1957, The study established that the species were; structurally glueable, Ekki has the highest density of 1.416g/cm3, the highest bending strength of the glue laminated timbers were obtained with 5 laminates (462N/mm2 for Ekki, 350N/mm2 for Baphia, and 308N/mm2 for Apa, at a moisture content of 30.885%, 26.215% and 28.730% respectively), the highest compressive strength were obtained with 5 laminates (43.4N/mm2 for Ekki, 41.3N/mm2 for Baphia, and 41.5N/mm2 for Apa) and highest tensile strength were obtained with 5 laminates (53.3N/mm2 for Ekki, 46.7 N/mm2 for Baphia and 70 N/mm2 for Apa). The strength of non-uniform beams were also determined with the highest bending, compressive and tensile strength of the glue laminated timbers recorded at 5 laminates (364N/mm2, 38.4N/mm2 and 66.7N/mm2 respectively). The study has therefore demonstrated that the timber species studied can be engineered to load bearing glued laminated structural elements and that the strength of the glue laminated timber increases with increase in the number of laminates.
