- Glued laminated timber (Glulam) is a structural product used for many years in countries with extensive experience in build timber structures, such as USA, Canada, Germany and Switzerland .As an engineered product, its production process requires an industry with quality control on manufacturing steps by trained manpower and raw material with compatible performance to requirements of products [2-6].To ensure that the Glulam element properties are in compliance with normative requirements and material strength is specified according to current codes, the final product must be tested under laboratory conditions .Nowadays, Glulam production in Brazil is still not so wide, being necessary greater disclosure of this technology, by uniting efforts of researchers, engineers, architects and industries. This is, therefore, a possible way to Glulam achieve visibility, competitiveness and economic viability in relation to other structural materials [1, 8-10].In order to provide competitiveness to Glulam in opposite to other building materials, such as reinforced concrete and steel, beyond of disclosure aiming to increase demand, it is also necessary to develop researches aiming lowering final product cost, that can occur with improvement of manufacturing processes as well as with raw materials economy [4, 6].Raw materials used to produce Glulam are wood and adhesive. Wood is the main element and adhesive is responsible to join together timber pieces for adequate shaping the final products. Cost of adhesive, in several cases, can be higher than wood. Therefore, usually it is preferable to use more wood and less adhesive. Consequently, more glue lines in structural elements will signify the higher products cost .Considering the possibility of economy and more rational use of glued laminated timber, this study aimed to investigate influence of glue lines number (or number of lamellae) on strength (MOR) and stiffness (MOE), in static bending, of glulam beams produced with CCA (Chromated Copper Arsenate) treated Pinus oocarpa.Besides, this research also aimed to evaluate the possibility of estimating these properties based on apparent density, once it's a wood characteristic of easy determination.
2. Material and Methods
- Wood species used for specimen fabrication was Pinus oocarpa, air-dried (12% moisture content) and CCA treated.Modulus of elasticity (MOE) and modulus of rupture (MOR) of Glulam beams (nominal dimensions 90 mm wide; 100mm height; and 1350mm length) were obtained using three point static bending tests (Figure 1), the same structural model proposed by Brazilian normative document  for small clear specimens.
|Figure 1. Three point static bending test|
|Figure 2. Experimental conditions to Pinus oocarpa glulam beams - 4 lamellae (a), 6 lamellae (b) and 8 lamellae (c)|
|Figure 3. Gluing CCA treated glulam beams|
|Figure 4. CCA treated Pinus oocarpa glulam beams|
3. Results and Discussion
- Table 1 shows mean , variation coefficients (Cv) and minors (Min) and higher (Max) values of modulus of elasticity (MOE) and modulus of rupture (MOR) on static bending as well as Glulam beams apparent density values.
|Figure 5. Normality tests: MOE (a) and MOR (b)|
|Figure 6. Variance homogeneity test: MOE (a) and MOR (b)|
|Figure 7. Adjustments by linear regression models: MOE (a) and MOR (b)|
- Results obtained in this study can led to conclude that variation of lamellae thickness (12,5mm, 16,70mm, 25mm) or glue lines number (3, 5, 7) did not influence significantly on strength and stiffness in bending, conducting to equivalent results.Thus, searching of economy associated with Glulam beams manufacturing, the best configuration investigated consists in using 25mm thickness lamellae, thereby decreasing adhesive amount, which provides:- reduction of costs involved in gluing;- handling and processing a smaller number of lamellae for final product manufacture;- reduction in the assembly time of beams by the industry.The visual classification of pieces enabled producing Glulam beams free from defects, which resulted in small variability found for values of mechanical and physical properties investigated, wherein the largest value of variation coefficient did not exceed 12%.Visual and mechanical classification in lamellae and tests on Glulam elements in structural size are highly recommended, because volume factor is important in using glulam.From estimation of mechanical properties as a function of apparent density, only to modulus of elasticity was found meaningful model. However, even though significant linear model to estimate MOE, the determination coefficient adjusted was less than 50%, evidencing that density did not led as good estimate in determining strength and stiffness values.
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