Engineered wood products (EWP) such as glulam beams are gaining more and more popularity due to several advantages resulting from the wood itself, as well as the constant search for structural materials of natural origin. However, building materials face some requirements regarding their strength. Thus, the study aimed to assess the static bending strength of structural beams produced with the use of pine wood, after the periodic loading of approximately 80 kN for a year. The manufactured beams differed in the type of facing layers, i.e., pine timber with a high modulus of elasticity and plywood. The produced beams, regardless of their structure, are characterized by a similar static bending strength. Moreover, it has been shown that the loading of beams in the range of about 45% of their immediate capacity does not significantly affect their static bending strength and linear modulus of elasticity.
Effects of Component Ratio of the Face and Core Laminae on Static Bending Strenght Performance of Three-Ply Cross-Laminated Wood Panels with Sugi (Cryptomeria Japonica)
In order to improve the bending strength performance of three-ply laminated wood panels and use them as construction-grade panel materials, twelve types of three-ply cross-laminated wood panels whose percentages of core lamina thickness versus total lamina thickness were 33%, 50%, and 80% were made with sugi (Japanese cedar), and the effect of component ratio of the face and core laminae on their static bending strength performance was investigated.
The moduli of elasticity (MOE), proportional limit stresses and moduli of rupture (MOR), perpendicular (C type) and parallel (C type) to the grain of face laminae markedly increased or decreased with increasing percentage of core lamina thickness. The percentages of core lamina thickness at which each strength property value of C type became equal to that of C type ranged from 65% to 80%. At each percentage of core lamina thickness, the MOE and proportional limit stress of C type were higher in C (45) specimens having perpendicular-direction lamina of 45° annual ring angle in the core than in C (90) specimens having perpendicular-direction lamina of 90° in the core, whereas there was little difference in MOR between C (45) specimens and C (90) specimens. For 45° specimens having the core lamina thickness from 60% to 70%, MOE as well as MOR parallel and perpendicular to the grain of face laminae exceeded the corresponding requirement values of structural plywood with 21.0-mm thickness specified in Japanese Agricultural Standards.
CLT panels consist of several layers of lumber stacked crosswise and glued together on their faces. Prototype Sugi CLT floor panels were manufactured and bending and internal shear tests were carried out under the different parameters of lumber MOE, number of layers, thickness of lumber and thickness of CLT panels. On the basis of above tests, internal shear strength, bending stiffness and moment carrying capacity were estimated based on the lumber properties by Monte Carlo method. Bending stiffness EI of CLT panels could be estimated by adopting parallel layer theory and equivalent section area. Experimental moment carrying capacity showed 12% higher value than the calculated moment carrying capacity by average lumber failure method, and also showed 45% higher value than the calculated moment carrying capacity by minimum lumber failure method due to the reinforcement of the outer layer by the neighboring cross layer. Experimental internal shear force of CLT panel showed 30% higher value than the calculated one.
Bending strength is a critical property of cross laminated timber (CLT) in structural applications, especially in floor of multi-story buildings. Therefore, this study was targeted to evaluate bending strength of CLT made out of poplar (populous alba). Polyurethane adhesive was used for constructing of CLT (300 g/m2). The thickness of planks was used in this study was 16 mm. The results have indicated that modulus of rupture (MOR) and modulus of elasticity (MOE) of CLT with 45o alternating transverse layer were increased 14 and 15%, respectively in comparison with 90o layers. Also, modulus of rupture (MOR) and modulus of elasticity (MOE) of CLT consist of layers with 4cm in width were increased 14 and 5%, respectively in comparison with layers 9cm in width. The results concluded that by layers with lower width, and also 45o alternating layer configuration could be constructed CLT from fast growing trees such as poplar with a considerable bending strength.
To develop a high-performance, lightweight cross-laminated timber (CLT) floor, this study tested the delamination performance between carbon fiber-reinforced plastic (CFRP) and CLT and the bending performance of a CFRP composite CLT that was differently reinforced according to the shape of CFRP. The test results showed that the soaking and boiling delamination between CLT and CFRP of the CFRP composite CLT produced by spreading a polyurethane (PUR) adhesive at 300g/m2 were both less than 5%, satisfying the Korean standard. Furthermore, the composite CLT (3ply) of which the entire outer surface of the tension laminae was reinforced with a CFRP plate (thickness: 1.2 mm) showed a mean MOE and a mean MOR higher by 27% and 48%, respectively, than those of the unreinforced CLT (3ply). Furthermore, even though the weight of this CFRP composite CLT was smaller than that of 5ply CLT by approximately 40%, its bending moment was measured higher by 14% than that of the 5ply CLT (thickness: 175 mm) fabricated by limited state design (LSD) as specified in PRG-320.
Various kind of in-plane bending tests of cross laminated timber (CLT) with different shapes have been previously carried out. The results indicate that the bending strength of CLT loaded in plane reduces as the number of layer increases. To evaluate this lamination effect on in-plane bending strength of CLT, a computational model based on Monte Carlo method was developed. The estimated bending strength showed the same tendency.
The bending behavior of T-section beams composed of a glulam web and an upper cross-laminated timber flange was studied. The influence of two fundamental factors on the bending strength and stiffness was considered: the wood species used for the webs and pretensioning with unbonded tendons. Sixteen specimens with a 9 m span were tested until failure: eight of them were nontensioned (4 Picea abies webs and 4 Quercus robur webs) and the other eight were pretensioned using threaded bars with 20 mm diameter anchored in plates fixed at the ends of the specimens (4 Picea abies webs and 4 Quercus robur webs). Pretensioning with unbonded tendons showed a clear improvement in the load capacity of the specimens with Picea abies webs, while the difference was not significant for the specimens with Quercus robur webs. Considering deflection, pretensioning gave the advantage of an initial precamber but also generated slight variations in the stiffness as a result of increasing the portion of the section that was in compression. The variation in the stiffness depended on the relation between the compressive and tensile moduli of elasticity parallel to the grain, and its influence on the deflection was analyzed using a finite element method.
This study presents the experimental evaluation of the behaviour of beams and columns made of Glued Laminated Guadua (GLG) bamboo. Flexural tests were conducted on structural size beams of various span lengths and two lamination orientations (horizontal and vertical) in order to evaluate the different capacities achieved according to the predominant induced stresses, bending or shear. Experimental results indicated a reduction of bending strength as the member’s size increased whereas lamination in the vertical direction presented 12% higher values of modulus of rupture (MOR), and 9% higher values of modulus of elasticity (MOE) compared to equivalent results for lamination in the horizontal direction. Additionally, compression tests were performed on structural size columns with various slenderness ratios and two lamination orientations. Although minor differences were found for lamination orientation, lower capacities were observed as the slenderness ratio increased. This experimental data is expected to be used in order to propose adjustment factors for structural size beams as well as the determination of the column stability factor.
The rising popularity of engineered-wood products, such as glued-laminated timber (glulam), as analternative to traditional sawn lumber encourages to fabricate glulam built-up sections that can expand the horizon of the use of this sustainable material in the construction of mid- and high-rise timber buildings. As a pilot investigation into the subject, five full-size built-up glulam box-section beam assemblies were experimentally examined under four-point flexural bending. Self-tapping screws were used in different patterns to form three beam assembly configurations. Each beam built-up section was made of four glulam panels, each of 44-mm thickness except the bottom flange panel that had 86-mm thickness. Experimental testing showed that reducing the spacing from 800 mm to 200 mm of the screws connecting the built-up section’s top and bottom flange panels to the web panels increased the beam flexural bending strength by about 45%. While reducing the spacing from 200 mm to 100 mm only for the screws connecting the bottom flange to the web panels over a distance equal to one-third beam span length from each support, where the maximum shear stresses existed, increased the beam flexural bending strength by an additional 10%.
The recent increasing trend of sustainable construction and advancement in the manufacturing of engineered wood have made products such as glued-laminated timber (glulam) and cross-laminated timber (CLT) preferred building materials. The intensifying demand for engineered-wood products in Canada also has prompted amendments to the building codes of several provinces by reducing the height restriction of timber structures from four to six stories. Unfortunately, the design of built-up timber beams has not yet been incorporated in most wood design standards worldwide. Thus, this lack of design guidelines brings forth the demand of acceptable methods to analyze, design and manufacture such built-up beam sections. The experimental research study detailed here in this thesis has been carried out to investigate the flexural bending behaviour of built-up glulam box-section beam assemblies fabricated using two engineered-control techniques at both, ambient and elevated temperatures. Seven full-size built-up glulam beam test assemblies were experimentally examined under four-point flexural bending to determine their maximum bending strengths at ambient temperature. Five of the seven beam assemblies tested at ambient temperature were fabricated using self-tapping screws; while the other two assemblies were built using industrial structural adhesive. The outcomes of ambient testing showed that reducing the spacing from 800 mm to 200 mm for the screws connecting the built-up beam section’s top and bottom flange panels to the web panels increased the beam flexural bending strength by about 45%. While reducing the spacing from 200 mm to 100 mm only for the screws connecting the bottom flange panel to the web panels over a distance equal to one-third beam span length from each support, where shear stresses are maximum, increased the beam flexural bending strength by an additional 10%. However, the experimental results of the glued beam assemblies showed considerable flexural bending strengths that are almost equal to the calculated strength of an equivalent hollow-section glulam beam. The influence of the bonding technique and configuration followed in fabricating the built-up beam sections, whether screwed or glued, was also investigated through observing the different failure modes that the built-up beam assemblies exhibited during testing. In addition, the experimental results of the ambient tests were used to verify the calculated bending strength capacity of the built-up glulam beams. Out of each of the glued and screwed assembly groups, only the strongest built-up beam assembly was examined under the effect of CAN/ULC-S101 standard fire while subjected to monotonic loading that was equivalent to the full-capacity design load of the weakest screwed built-up beam assembly with 200-mm screw spacings. The fire resistance tests were conducted using the large-size fire testing furnace accommodated at Lakehead University’s Fire Testing and Research Laboratory (LUFTRL). Outcomes of the fire resistance tests revealed that the glued built-up beam assemblies experienced greater mid-span deflections as well as beam end rotations in comparison to the screwed built-up beam assemblies. This inferior behaviour can be interpreted to the low fire resistance of the adhesive used in fabricating the built-up beam assemblies, which excessively limited the beam’s shear and bending strengths at elevated temperatures. On contrary, the self-tapping screws noticeably helped in keeping the built-up beam assemblies intact for longer time during fire testing even when the screws were exposed to direct fire heating.
){kind=link}
+Made+Out+of+Poplar+(Populus+Alba)){kind=link}
