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Planar shear and bending properties of hybrid CLT fabricated with lumber and LVL

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Abstract

Planar (rolling) shear properties in cross laminated timber (CLT) is an important factor that should be considered for CLT structural components with short span or openings. The planar shear properties of SPF (Spruce-pine-fir) dimension lumber and laminated veneer lumber (LVL) were measured using a modified approach in this study. The failure modes in planar shear tests were investigated by visual inspection and optical microscope. Hybrid CLT (HCLT) was fabricated using lumber and/or LVL, and its bending properties (in major strength direction) were evaluated. It was found that SPF had higher planar shear strength and modulus than LVL. The failure mode of HCLT with LVL as cross layer in planar shear test was shear failure along the glue line direction, however, the typical failure modes of HCLT with SPF as cross layer in planar shear test included rolling shear failure along the growth ring direction, shear failure along the wood ray direction and shear failure along glue line direction. The bending properties of the generic CLT had been improved by using LVL as parallel layers and been reduced by using LVL as cross layer. The planar shear failure of cross layer in the zone between loading point and support point was the typical failure mode of CLT and HCLT in bending test.

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... The rolling shear failure mode of lumber is closely related to its macroscopic characteristics. Wang et al. [27] found that the rolling shear failure of SPF dimension lumber mainly happened at the weak macroscopic characteristics in the radialtangential (RT)section of lumber, such as the junction of earlywood and latewood and wood rays, as shown in Figure 12. On the other hand, Yang [28] used the acoustic emission (AE) technique to monitor the changes of AE parameters during the rolling shear failure process of CLT. ...
... Some studies have been conducted on the HCLT fabricated with sawn timber and SCL/ wood-based panels. The SCL/ wood-based panels employed in these studies included LVL, LSL, oriented strand lumber (OSL), COSB and plywood [27][28][29][30][31][32][33][34][35]. Wang et al. [29] fabricated the HCLT by mixing SPF and LSL, and when LSL was used as the outer layer (longitudinal layer), the modulus of elastic (MOE) and modulus of rupture (MOR) of HCLT increased by 19% and 36%, respectively, compared with the generic lumber CLT. ...
... Davids et al. [34] also obtained a similar research conclusion that the use of LSL hybrid structure could improve the bending performance of CLT, mainly because LSL had better mechanical properties (rolling shear properties and tensile properties) and more homogeneous mechanical properties than solid wood. Wang et al. [27] studied the mixing of SPF and LVL according to different layups and formed three kinds of HCLT. It was found that due to the low rolling shear properties of LVL, the bending mechanical properties of CLT could be greatly improved only when LVL was placed in the outer layer. ...
Chapter
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Cross-laminated timber (CLT) is a popular engineering wood product in recent years. It has some characteristics of configuration and mechanical properties, which makes it an excellent building material for floor, roof and other places. In Europe and North America, lots of middle and high-rise buildings have adopted CLT as their main structural component. CLT has recently been used to construct public buildings in China. As a building material, the lower rolling shear properties of CLT has always been a concern. To overcome this shortcoming of CLT, the structural composite lumber and bamboo have been employed to develop hybrid CLT. This chapter also presents the latest development and advances of CLT in China.
... Compared with sawn timber, SCL or structure panels have better mechanical properties and higher utilization of raw materials. Some studies have been conducted on the HCLT fabricated with sawn timber and SCL/structure panels including laminated veneer lumber (LVL), laminated strand lumber (LSL), oriented strand lumber (OSL), construction oriented strand board (COSB) and plywood [8][9][10][11][12][13]. Rolling shear properties are the key properties for CLT under out-of-plane loading, so the rolling shear properties of these SCL/structure panels were first tested in the studies. ...
... LVL, was found had low rolling shear properties. Wang et al. evaluated the planar (rolling) shear properties of LVL and SPF with the same aspect ratio 2.34 and found the planar shear modulus and strength of LVL were 43.62% and 24.11% lower than those of SPF, respectively [8]. Then the bending and shear properties of HCLT having various layup structures were evaluated by experiments, theoretical calculation or numerical modeling. ...
... When loaded in major or minor strength direction, the 3-layer HCLT, having COSB as transverse layer, had 87% or 217% higher shear resistance than those of generic SPF CLT, respectively [12]. The average modulus of elasticity (MOE) and modulus of rupture (MOR) in the major direction of generic SPF CLT were improved by 18% and 5% when using LVL as longitudinal layers, respectively, but these properties were reduced by 9% and 10% when using LVL as transverse layers, respectively [8]. ...
Article
Using bamboo and timber to manufacture cross-laminated timber-bamboo (CLTB) composites could utilize the advantages of two material to improve the mechanical properties and expand the raw material source of cross-laminated timber (CLT). To explore the feasibility of using engineered bamboo as CLT lamination, the rolling shear properties of two bamboo scrimbers and one bamboo plywood were evaluated. Two types of CLTB specimens, using bamboo scrimber as transverse layer or as both transverse layer and the outermost longitudinal layer, were developed in this study. The bending properties of CLTB and generic Spruce-pine-fir (SPF) CLT specimens were evaluated by dynamic tests and third-point bending tests, respectively. The shear analogy method was employed to calculate the apparent bending stiffness of CLT/CLTB specimen. The results indicated that the rolling shear modulus and strength of bamboo scrimber (group RB(F)-4.5) were 92.81% and 98.64% higher than those of bamboo plywood, respectively, and were 330.19% and 121.13% higher than those of SPF dimension lumber, respectively. The CLTB specimens, group BWBWB, had 23.69% and 60.50% higher apparent bending modulus and peak load than those of generic SPF CLT specimens. Most of the CLTB bending specimens had main failure mode of tensile failure in the bottom layer which replaced rolling shear failure in transverse bamboo scrimber layer. The apparent bending stiffness values of CLT/CLTB specimens obtained from dynamic test and shear analogy method were in good agreement with the static experimental values. The results presented in this paper can provide fundamental basis for supporting the potential engineering application of CLT panel products fabricated with bamboo scrimber.
... Timber boards are orthotropic in nature, where the mechanical properties vary along the longitudinal, tangential, and radial direction [7]. To improve performance of CLT under out-of-plane bending, some researchers investigated the use of engineered wood product such as laminated strand lumber (LSL) and laminated veneer lumber (LVL), as cross-layers [8,9]. ...
... This observations are used to develop an equation for modification co-efficient. The form of the equation was chosen to be 1 (9) where d is the depth of the panel, GRT is the rolling shear modulus, and L is the span length. The rationale for this form of equation for Equation (9) are the conclusions that were explained in Section 5.1, which are that the magnitude of c with increasing length approaches 1 and is positively correlated to depth of the panel and the rolling shear modulus. ...
... The form of the equation was chosen to be 1 (9) where d is the depth of the panel, GRT is the rolling shear modulus, and L is the span length. The rationale for this form of equation for Equation (9) are the conclusions that were explained in Section 5.1, which are that the magnitude of c with increasing length approaches 1 and is positively correlated to depth of the panel and the rolling shear modulus. The summary of the results obtained from the parametric study is illustrated in Figure 15. ...
Article
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Cross-laminated timber (CLT) is an engineered wood product made up of layers of structurally graded timber, where subsequent layers are oriented orthogonally to each other. In CLT, the layers oriented in transverse direction, generally termed as cross-layer, are subjected to shear in radial-tangential plane, which is commonly known as rolling shear. As the shear modulus of cross-layers is significantly lower than that in other planes, CLT exhibits higher shear deformation under out-of-plane loading in contrast to other engineered wood products such as laminated veneer lumber (LVL) and glue laminated timber (GLT). Several analytical methods such as Timoshenko, modified gamma and shear analogy methods were proposed to account for this excessive shear deformation in CLT. This paper focuses on the effectiveness of Timoshenko method in hybrid CLT, in which hardwood cross-layers are used due to their higher rolling shear modulus. A comprehensive numerical study was conducted and obtained results were carefully analyzed for a range of hybrid combinations. It was observed that Timoshenko method could not accurately predict the shear response of CLTs with hardwood cross layers. Comprehensive parametric analysis was conducted to generate reliable numerical results, which were subsequently used to propose modified design equations for hybrid CLTs.
... In addition to the softwood and hardwood, structural composite lumbers (SCL), like laminated strand lumber (LSL), laminated veneer lumber (LVL), and oriented strand lumber (OSL), were also used to fabricate HCLT, aiming to improve the mechanical properties of CLT. In the study of Wang et al. [13,14], LSL and LVL were used to fabricate the 3-layer HCLT specimens. Compared with regular CLT, the MOE and MOR were increased by using LSL or LVL as outer layers. ...
... The rolling shear cracks would propagated through the transverse layer, which eventually caused bonding line delamination failure, Fig. 3(b). These rolling shear and combined bonding line delamination were reported in some previous studies [8,13,14,16,17,26]. For the COSB CLT specimens (groups 3-A5 and 5-A5), which only made of COSB panel, the dominant failure mode was shear failure of COSB in the middle of COSB panel thickness, Fig. 3(c). ...
... This improvement is attributed to the higher mechanical properties in minor strength direction of COSB. Other studies also found that using EWPs, i.e., LSL and OSL, as transverse layer would improve the bending and shear properties of CLT [13][14][15][16][17]. Compared group 3-A4 with group 3-A1, which had different longitudinal layer, the shear resistance of group 3-A4 was 50% higher than that of group 3-A1. ...
Article
Recently, to enlarge the source of raw materials and improve the mechanical properties of cross-laminated timber (CLT), some local wood species, hardwood and Engineering wood products were used to fabricate CLT. This project studied mainly the feasibility of using construction oriented strand board (COSB) to fabricate hybrid CLT (HCLT). The shear properties of the HCLT were reported in this paper. The mechanical properties of COSB in major and minor strength directions were firstly obtained by various span bending tests and compression tests. The shear resistance and stress in major and minor strength direction of five groups of 3- and 5-layer HCLT, having different lay-up arrangements, were evaluated by experiments, shear analogy theory as well as FE methods. Results showed COSB had higher mechanical properties in minor strength direction compared with SPF dimension lumber. Different HCLT groups had different failure modes observed for major and minor direction. Except to the rolling shear failure of SPF transverse layer and tension failure of gaps between the lumber of the bottom layer, the longitudinal and transverse shear delamination failures and tension failure of COSB were observed during four-point short-span bending tests of HCLT. All the HCLT specimens had higher shear resistance than that of regular CLT with the same number of layer. The difference of the shear resistance between the two strength directions of HCLT decreased as the number of COSB layer increased. In addition, the shear resistance and stress of HCLT can be predicted according the shear analogy theory, and the developed FE models can predict the shear stress of HCLT well. The results presented in this paper can provide fundamental basis for supporting the potential engineering application of CLT panel products fabricated with COSB.
... spruce-pine-fire (SPF), D. Fir-L (Douglas fir-larch) and Hem-Fir lumber are assumed 50 MPa for design purpose in North American CLT handbook (Gagnon and Pirvu 2011), which is thought to be too low. The mean rolling shear strength and modulus values of No. 2 SPF were measured to be 1.4 MPa and 85 MPa, respectively (Wang et al. 2017). In recent years, hardwood, e.g. ...
... So the 5% quantile value f R,05 =2.24 MPa of poplar boards without pith again exceeds the specified values of softwood. It is about 2.5 times of the characteristic f R of NO. 2 spruce-pine-fir (0.88 MPa) measured by Wang et al. (2017). These above results of rolling shear properties of the poplar boards indicate that fast-growing poplar wood has great potentiality to been used as cross-layer in CLT plates. ...
... During the actual tests, the initial failure may be caused by one of the above described mechanisms, however, with the increase of either load or displacement, the combination of three different failure modes can be observed in the cross layers of a specimen due to very complicated stress redistributions. The findings here agree well with the failure mechanisms reported other previous study (Nie 2015, Wang et al. 2017). Nie (2015) recorded the detailed failure process of CLT cross layers with high speed camera and categorized the initial failure modes into three types, tension perpendicular to grain type, rolling shear type and marginal type. ...
Article
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Rolling shear modulus (GR) and strength (fR) of the cross layers are decisive mechanical properties in cross-laminated timber (CLT) plates. The influences of macro characteristics, such as annual ring orientation, distance to pith, and presence of pith on the rolling shear properties of fast-growing poplar boards were evaluated throughout this study. It were found the presence of pith had significant influence on the rolling shear properties of poplar board. Distance to pith and annual ring orientation both had effects on the rolling shear properties jointly. The rolling shear properties increase with the increase of distance to pith. The mean rolling shear modulus and characteristic rolling shear strength values of the poplar wood were determined to be 177 MPa and 2.24 MPa, respectively, which indicates a great potential of using poplar wood as the cross-layers in CLT.
... However, replacing the core layer by LSL had a negative effect (nearly 13% and 24%) on MOE and MOR values, respectively. In another study, Wang et al. [8] investigated hybrid CLT fabricated with laminated veneer lumber (LVL) as face layers to enhance the flexural strength of CLT. They reported an increase of 18% and 5% in MOE and MOR values of the CLT panel, respectively, by using LVL as the major strength layers. ...
... Several studies have attempted to increase the flexural strength of CLT panels using compressed and thinner planks [16,18,28], hybrid LSL, LVL [7,8,10], various combinations of wood species [29], and various layer arrangements [18]. Changing the layer configuration of CLT panels, on the other hand, may be considered as an alternative way to increase the bending performance of CLT panels in two strength axes. ...
Article
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This study aimed to investigate the effect of layer arrangement on bending properties of CLT panels made from poplar (Populus deltoides L.). A total of 20 three-layer CLT panels with the same dimensions of 1300 × 360 × 48 mm3 (Length, Width, Thickness) were fabricated in five configurations: 0/30/0, 0/45/0, 0/90/0, 45/0/45, and 45/45/45. The apparent modulus of elasticity (MOEapp), modulus of rupture (MOR) and apparent bending stiffness (EIapp) values in major and minor axes of CLT panels were calculated using experimental bending testing. In the major axis, the highest values of MOR, MOEapp, and EIapp were obtained from the 0/30/0 arrangement, while the least values resulted from the arrangements of 90/60/90 and 90/45/90 in the minor axis. Besides, in all arrangements, the average of the experimental apparent bending stiffness values (EIapp,exp) of specimens was higher than that of the shear analogy apparent bending stiffness values (EIapp,shear). The bending and shear stress distribution values over the cross section of samples were also estimated using the finite element method. Moreover, the numerical apparent bending stiffness (EIapp,fem) values of samples were compared to experimental apparent bending stiffness (EIapp,exp) values. Based on experimental and finite element method results, in all groups of layer arrangements, the EIapp,fem values concurred well with the EIapp,exp values.
... Previous studies on CLT have mainly focused on the properties of the material itself such as bending, tensile, shear, and compressive strength [10][11][12][13][14][15][16]. Effects of thickness, wood species, lamina combinations, and so on [10][11][12] on the mechanical properties and properties of the CLT composites [13,14] were investigated. ...
... Previous studies on CLT have mainly focused on the properties of the material itself such as bending, tensile, shear, and compressive strength [10][11][12][13][14][15][16]. Effects of thickness, wood species, lamina combinations, and so on [10][11][12] on the mechanical properties and properties of the CLT composites [13,14] were investigated. Our group also conducted some studies on CLT such as the size effect and prediction of compressive strength [15,16]. ...
Article
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Cross-laminated timber (CLT) elements are becoming increasingly popular in multi-storey timber-based structures, which have long been built in many different countries. Various challenges are connected with constructions of this type. One such challenge is that of stabilizing the structure against vertical loads. However, the calculations of the stability bearing capacity of the CLT members in axial compression in the structural design remains unsolved in China. This study aims to determine the stability bearing capacity of the CLT members in axial compression and to propose the calculation method of the stability coefficient. First, the stability coefficient calculation theories in different national standards were analyzed, and then the stability bearing capacity of CLT elements with four slenderness ratios was investigated. Finally, based on the stability coefficient calculation formulae in the GB 50005-2017 standard and the regression method, the calculation method of the stability coefficient for CLT elements was proposed, and the values of the material parameters were determined. The result shows that the average deviation between fitting curve and calculated results of European and American standard is 5.43% and 3.73%, respectively, and the average deviation between the fitting curve and the actual test results was 8.15%. The stability coefficients calculation formulae could be used to predict the stability coefficients of CLT specimens with different slenderness ratios well.
... However, this specific orientation under out-of-plane loading shows significant planar (rolling) shear deformations because, in the radial-tangential (RT) plane, wood has a relatively low shear modulus. To address this issue, many studies have been performed, including the measurement of the planar shear properties [12], improvement of the planar shear properties [13] and evaluation of the effects of CLT configuration and manufacturing parameters on the shear and bending properties of CLT [14][15][16][17]. ...
... where A is the total cross-sectional area of the CLT panel and coefficient c is a reduction factor eff total I c I = (13) where Itotal and Ieff are the total and effective moment of inertia for the major strength axis, respectively. Ieff is the effective moment of inertia of the panel accounting only for the layers with laminations oriented parallel to major strength axis ...
Article
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Composite sandwich panels were manufactured by gluing plywood skins to either bamboo rings to produce Bamboo Core Sandwich (BCS) panels or to peeler core rings to produce Peeler Core Sandwich (PCS) panels. Single and double core layer panels were made. The optimum adhesive spread rate was identified through conducting shear bond tests. The manufactured panels were physically tested in standard bending (using four-point) and shear (using three-point) tests. Results were compared to the test results of conventional Cross-laminated Timber (CLT) panels with almost similar depth. Under bending action, both the BCS and PCS panels showed tensile failure in the plywood, while the plywood in compression exceeded its plastic limit at the ultimate load. In shear, BCS panels failed due to the loss of shear interface contact between bamboo core rings and the plywood skins, whereas PCS panels showed local indentation/ bond failure between the peeler core rings and the plywood skins. No significant improvements were observed in the double-layer panels compared to single-layer panels in bending. However, in shear, double-layer panels showed more consistent capacities. One PCS panel with thicker plywood skins and less peeler core rings (PCS-TH) was manufactured, and was shown to achieve 0.77 times the bending stiffness-to-weight ratio of the commercial CLT panel. Reduced weight, lower material costs, ease of manufacturing and usage of sustainable/waste products, make the proposed sandwich panels a potential alternative for CLT in terms of structural performance. Moreover, the proposed peeler core sandwich panels displayed better ductile performances in bending and shear compared to CLT suggesting it could be a preferred product choice in some building applications.
... Wang et al. [77,78] tested the bending and shear performances of hybrid CLT (HCLT) manufactured by pine lumber and laminated veneer lumber (LVL) as well as those of HCLT manufactured by SPF and LVL. The three-layer HCLT with LVL as outer layers or core layer could provide better bending or shear properties, compared to the pure pine CLT [77]. ...
... The three-layer HCLT with LVL as outer layers or core layer could provide better bending or shear properties, compared to the pure pine CLT [77]. However, for the three-layer pure SPF CLT, its bending properties were reduced by replacing the SPF with the LVL in the core layer [78]. Davids et al. [79] tested the bending and shear performances of HCLT manufactured by SPF and laminated strand lumber (LSL). ...
Article
Both wood and bamboo are renewable anisotropic materials with a long application history in human society. Engineered wood or bamboo aiming to mitigate the variability of the natural material can provide better material properties and structural performance, compared to original sawn lumber or raw bamboo. In this paper, a state-of-the-art review was conducted on three types of novel engineered wood composites, namely fiber reinforced polymer (FRP) reinforced glulam, cross-laminated timber (CLT), and wood scrimber, as well as three types of novel engineered bamboo composites, namely laminated bamboo lumber (LBL), glued-laminated bamboo (glubam), and bamboo scrimber, with particular attentions to their manufacturing technologies, modeling approaches, and mechanical properties. Then, for these novel engineered wood/bamboo composites, a comprehensive comparison was conducted on their mechanical properties and on their densities. Finally, several cases of structural applications were respectively illustrated, in which these aforementioned engineered wood/bamboo composites were adopted as main building materials. Potentials of applying these engineered wood/bamboo composites for structures were confirmed, and their possible existing drawbacks were also discussed.
... The average out-of-plane shear strength values of CLT specimens calculated based on shear analogy method using the maximum load from FPB and TPB tests were 1.15 and 1.36 MPa, respectively. These values agree well with the values of the three-layer CLT specimens obtained from the modified compression shear testing method in previous studies [11,27]. The RS strength of 2 × 4'' and 2 × 6'' SPF dimension lumber obtained by Gong et al. [11] were 0.92 and 1.29 MPa, and the RS strength of SPF dimension lumber measured by Wang et al. [27] was 1.41 MPa. ...
... These values agree well with the values of the three-layer CLT specimens obtained from the modified compression shear testing method in previous studies [11,27]. The RS strength of 2 × 4'' and 2 × 6'' SPF dimension lumber obtained by Gong et al. [11] were 0.92 and 1.29 MPa, and the RS strength of SPF dimension lumber measured by Wang et al. [27] was 1.41 MPa. ...
... Scientists from NFU studied the hybrid CLT fabricated with lumber and laminated veneer lumber (LVL) or different wood species. And the test data of rolling shear, bending, and inter-laminar shear helped improve the rolling shear performance of the CLT and provided a reference for engineering applications Wang et al., 2016;Wang Z Q et al., 2017). Wang (2017) studied the effect of macroscopic characteristics of sawn timber such as density, annual ring, pith distance, pith and wood species on rolling shear properties of cross layer of softwood CLT. ...
... And a good connection of butt joint of main side material and oblique-nailed joint of the STS on both left and right directions was proposed. In order to evaluate the influence of laminate materials on the lateral performance of the CLT shear wall, they tested single lumber CLT and hybrid CLT of lumber and laminated veneer lumber (LVL) under the unidirectional and low-cycle repeated load and the hybrid CLT shear wall exhibited good performance (Wang Z Q et al., 2017). ...
Article
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As a new type of green low-carbon engineered wood product, cross-laminated timber (CLT) is widely used in various types of wooden buildings in Europe and North America, and the number of high-rise wood construction is also increasing. Based on the introduction of the structural characteristics of the CLT and the development status of the CLT in developed countries, this paper focused on the review of the status of research and development of the CLT in China, with an emphasis on the breakthrough technologies of new bamboo-wood composite CLT developed. Finally, the prospects of the CLT in China were discussed.
... According to ANSI (2018), several wood species are permitted to be used in one CLT panel if the wood has the same mechanical properties and has a specific gravity of more than 3.5, like softwood. Softwood has a homogeneous structure, so most CLTs are produced using softwood (Aicher et al. 2016;Marko et al. 2016;Wang et al. 2017;Zhou et al. 2020). The production of CLT from softwood has limited raw materials, thus large quantities of raw materials are needed (Mallo and Espinoza 2014). ...
Article
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The purpose of this study was to evaluate the characteristic of cross-laminated timber (CLT) made from puspa (Schima wallichii) wood, coconut (Cocos nucifera) trunk, and their combination using a polyurethane (PU) adhesive. The manufacturing of CLT begins with the characterization of the adhesive and wood materials used in this study. The CLT panels are made with dimensions of 100 cm × 30 cm × 3.6 cm. The laminate was organized into three layers with the face/core/back, namely puspa wood (PPP), coconut trunk (CCC), and their combination (PCP and CPC), perpendicular to each other using polyurethane adhesive with a glue spread of 160 g.m-2. The physical and mechanical properties of the CLT were assessed according to the JAS 3079 (2019) standard. The results showed that the polyurethane adhesive used in this study could cure optimally at a temperature of 30°C for 200 minutes. Puspa wood and coconut trunk had different physical and chemical properties but had similar wettability to polyurethane adhesives. The physical and mechanical characteristics of coconut CLT were better than puspa CLT. Based on the overall test results, the puspa hybrid CLT is better than the single wood species of the CLT. In contrast to coconut hybrid CLT, the single CLT of CCC was better than its hybrid CLT.
... In addition, applying CLT in buildings can be economically advantageous due to the fast and easy construction process (Karacebeyli and Douglas 2013) and efficient circular economic practices (Neykov et al. 2020). However, CLT applications tend to be limited to softwood species as raw materials (Aicher et al. 2016;Marko et al. 2016;Wang et al. 2017;Zhou et al. 2020). Another disadvantage of CLT is that it requires many raw materials (Mallo dan Espinoza 2014), so it is fundamental to utilize hardwood with high production. ...
Article
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This study aimed to evaluate the physical and mechanical properties of cross-laminated timber (CLT) characteristics from mangium (Acacia mangium) and puspa (Schima wallichii) woods and their combination using polyurethane (PU 1.2) adhesives. The manufacture of CLT began with basic adhesive characterization and thermo-mechanical analysis. Wood material's physical and chemical properties were also tested with its response to the PU 1.2 wettability. The CLT (100 ´ 30 ´ 3.60) cm 3 was manufactured with 160 g/m 2 glue spread at a pressure of 0.80 MPa for 200 minutes. The CLT panels were characterized refers to the JAS 3079 standard. The results show that PU 1.2 had a gelatination time of 182.1 minutes at 25°C, was able to form urethane groups, and experienced an increase in storage modulus at 35°C. Mangium and puspa woods have different physical and chemical properties, but they interact similarly with PU 1.2 wettability. Puspa CLT panel has a higher density than mangium but lower dimensional stability. The bending mechanical properties of hybrid puspa-mangium-puspa CLT were able to match puspa CLT and have one sample of shear strength that met the JAS 3079 standard in both grain directions. Therefore, hybrid puspa-mangium-puspa CLT has the potential to be developed to improve its dimensional stability and mechanical properties.
... The SPF was found to have a higher plane shear strength and modulus than the LVL [26]. The bending properties of common CLTs improved with the use of LVL in parallel layers, whereas they could be seen to decrease with the use of LVL in the cross-layer. ...
Article
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Timber and timber products are renewable materials that, due to their durability and strength properties, meet the requirements of the construction industry, are widely used in buildings. An analysis of the scientific literature has shown that there is a lack of detailed research that fully investigates the influence of the rate of increase of the moisture content of the timber on the mechanical and, especially, the strength properties of the LVL panels. Upon immersion into water of the bottom of the specimen, the water starts rising quite quickly at the edge of the specimen, and the first six hours are the most critical. The levels of water rise inside the LVL specimen were less significant than at the edges. It was found that water significantly affects the bending strength of the panels, which, when the strength of the wet panel compared to the strength of the dry panel, decreases to 45% after one soak cycle and almost to 52% after two soak cycles. The tensile strength of the wet specimens is ~40% less than that of the dry specimens. The strength of the panels that were dried back to their initial state was found to be sufficient again, different from the initial strength only within the error limits; the strength properties of the building structure will not be affected.
... The growing interest on CLT for design purposes and its great mechanical properties, have led several authors to analyze deepen its mechanical characteristics as bending, tensile, shear, and compressive strength [9][10][11][12][13][14][15]. In terms of composition, literature studies mostly emphasized the potential and benefits of CLT panels made with wood species other than fir and spruce [16][17][18][19], and a minor attention has been spent for native hardwoods species such as beech, yellow-poplar and tropical hardwood (i.e. ...
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This paper investigates the column buckling behaviour of three-layer Cross Laminated Timber (CLT) panels under compression, from both the experimental and numerical point of view. The main aim of present study is hence to define the expected load-bearing capacity for these composite CLT solutions, and to assess the typical fracture mechanism for two different series of specimens of possible technical interest for construction applications. To this aim, a total of 14 column buckling experiments is carried out. First, a set of 7 homogeneous speciemens (“HO” series), which are entirely made of beech, are investigated. Their load-bearing capacity is compared with the column buckling performance of 7 hybrid specimens (“HB” series), whose inner layers are made of Corsican pine. Overall, the experimental analysis gives evidence of a rather stable column buckling capacity for CLT panels, with evidence of major failure mode due to out-of-plane bending phenomenam, but also rolling shear and delamination. Finally, further assessment of experimental evidences is provided by extended analytical calculations (based on existing formulations, including the Eurocode 5 approach) and even Finite Element (FE) numerical analyses for the examined three-layer CLT compositions. Comparative results are discussed in terms of structural performance, capacity, weakness of analytical models for CLT solutions.
... Recently, some studies are carrying out to fabricate hybrid CLT (HCLT) with hardwoods, structural composite lumber (SCL) or structural panels, in order to improve the mechanical properties of CLT and expand the sources of CLT laminations. The SCL and structural panels that have been studied include laminated veneer lumber (LVL), laminated strand lumber (LSL), oriented strand lumber (OSL), oriented strand board (OSB) and plywood [2][3][4]. These researches show that adding SCL or structural panels to CLT can improve the production efficiency, fire resistance and mechanical properties of CLT, due to their high mechanical properties, low variability of physical and mechanical properties, and large product size [5]. ...
Article
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The differences of physical and mechanical properties of different laminations, such as softwood, hardwood or other structural composite lumber, in hybrid cross-laminated timber (HCLT), lead to their dimensional stability and bonding performance more complex than generic cross-laminated timber (CLT). In this paper, the spruce-pine-fir (SPF) dimension lumber and construction oriented strand board (COSB) were employed to fabricate HCLT. The effects of four configurations and three adhesives on the dimensional stability and bonding performance of CLT and HCLT were evaluated in term of the water absorption (WA), thickness swelling (TS), block shear strength (BSS), wood failure percentage (WFP) and rate of delamination (RD). The results showed that with the increase of the COSB laminations, the WA of HCLT specimens decreased, and the values of TS, BBS and WFP increased. The configuration had a significant influence on the dimensional stability, BBS and WFP of the specimen. The adhesive had a significant influence on the dimensional stability and some bonding performances of the specimen. The phenol resorcinol formaldehyde (PRF) specimens had the lowest average RD value compared with the one-component polyurethane (PUR) and emulsion polymer isocyanate (EPI) specimens. Failures were prone to occur in the middle of the thickness of COSB lamination during block shear and delamination tests. The outcome of this paper could help the engineering application of HLCT.
... The mixedspecies CLT can be made out of softwood and hardwood, different hardwood or softwood species. Moreover, engineered wood composites, such as oriented strand board (OSB), laminated veneer lumber (LVL), and plywood, have also been used for producing hybrid CLT to expand their use in mid to high-rise building construction [20][21][22][23][24][25][26][27]. ...
Article
The utilization of rubberwood (Hevea brasiliensis) and coconut wood (Cocos nucifera L.), the essential economic crops in Thailand and tropical countries, was proposed for manufacturing mixed species/density cross-laminated timber (CLT) for building construction. Six 3-layer CLT configurations, which are composed of either medium-density (600 – 799 kg/m³) rubberwood (MRB) or coconut wood (MCC) or high-density (800 – 999 kg/m³) coconut wood (HCC) laminations, were determined considering the mechanical properties and material costs. The outer layers of the control MCC CLT were replaced with either MRB or HCC to improve its mechanical properties, while either outer or core layers of the control MRB CLT were replaced with HCC to reduce its material cost. The material properties of the three wood types and the six CLT configurations were examined. The densities of the produced CLTs were not affected by the chosen manufacturing parameters showing a strong correlation to the lamination's density. From the bonding performance perspective, the mixed-species approach significantly increased the average wood failure percentage of the control MRB CLT. However, only the control MCC CLT achieved the average wood failure percentage greater than 80%, as required in North America's CLT standard. The compressive strength properties of the CLTs in their major strength directions, σclt, were governed by the outer laminations' parallel-to-grain compressive strength. Unlike softwood CLTs, neglecting the load sharing contribution of the core layer in the σclt estimation resulted in 15% underestimation. Rolling shear strength, τrs, was determined by the core laminations regardless of the CLT layups. MRB achieved the highest τrs followed by HCC and MCC, and all values were significantly larger than the common softwood used in CLT production. The results imply that the mixed species/density approaches can effectively improve the mechanical properties of the coconut wood CLT and reduce the material cost of rubberwood CLT without compromising structural performance.
... The Foschi and Yao model has been used successfully to study the influence of the DOL effect on the strength characteristics of dimension lumber, CLT, and other engineered wood products [5,[12][13][14]. To improve CLT's mechanical properties and expand its raw material sourcing, hybrid CLT (HCLT), which is fabricated from various kinds of solid wood laminates and structural composite lumber and bamboo-such as laminated veneer lumber, oriented strand board (OSB), laminated strand lumber (LSL), and bamboo scrimber-has been developed recently [16][17][18][19][20][21][22][23][24][25]. The production efficiency, fire resistance, and mechanical properties of HCLT were improvements on those of regular CLT [20]. ...
Article
Given the nature of cross-laminated timber (CLT), with an orthogonal arrangement and rolling shear characteristics of transverse layers, it has a more complex duration-of-load (DOL) effect than other engineered wood products, such as glued-laminated timber. Developing hybrid CLT (HCLT) with structural composite lumber, which can improve the mechanical properties and material sources of CLT, is gaining increasing interest. Construction oriented strand board (COSB) and spruce-pine-fir (SPF) dimension lumber were used to fabricate HCLT specimens for this study. The regular SPF CLT and HCLT specimens having different lay-ups and numbers of layers were subjected to low-cycle fatigue bending and shear loading tests. The Foschi and Yao damage accumulation model was calibrated using the test results. The DOL factors for the CLT and HCLT specimens were calculated using the stress ratio evaluation method. Results showed that the primary failure modes for the fatigue test specimens were the same as those observed in previous short-term ramp loading tests, and a good fit was observed between the model's predictions and the test data. The DOL factor corresponding to a load duration of 50 years, for a three-layer shear CLT specimen, was determined to be 0.53, which was lower than that recommended in CSA O86-19. The fatigue life and long-term performance of CLT were improved by using COSB panels as CLT layers. The HCLT specimens that used COSB only as the transverse layer showed advantages in fatigue life, long-term performance, and practical applications.
... The experimental results indicated that the existence of LSL in the core layer of CLT played a significant role in the increase of the bending strength at failure by 23% through a declination of rolling shear failure. In another study, Wang et al. [14] calculated the bending strength of hybrid CLT fabricated using lumber and/or LVL laminated veneer lumber (LVL), and concluded that bending properties of the CLT increased using LVL as parallel layers and decreased using LVL as a cross-layer. ...
Article
The purpose of this research was to investigate the structural out-of-plane bending performance of three-layer hybrid cross-laminated-timber manufactured from outer layers of fast-growing Poplar (Populus alba) and a cross-layer of Iranian Beech species (Fagus orientalism) using polyurethane as a binder. The bending performance of the hybrid CLT was determined in both major and minor axis orientations in diverse span-to-thickness ratios by experimental and theoretical methods. It was compared to that of Poplar CLT reported in our previous research. The experimental and theoretical methods indicated that the bending performances comprising maximum shear force (Vmax), maximum bending moment (Mmax), apparent modulus of elasticity (MOEapp), modulus of rupture (MOR), shear strength (τmax), effective bending stiffness (EIeff), and effective shear stiffness (GAeff) of hybrid Poplar-Beech CLT in all span-to-thickness ratios at both major and orientations were greater than those of Poplar CLT. Moreover, in both orientations, the results of bending and shear stress distributions of the specimens showed that the hybrid Poplar-Beech CLT had greater load-carrying capacity than Poplar CLT. However, in both orientations, the failure modes of hybrid CLT were similar to those of Poplar CLT. The experimental dominant failure modes in the major axis orientation of CLTs were rolling shear and delamination, while tensile failure and crack were mainly observed in the minor axis orientation. In summary, in comparison with Poplar CLT, both experimental and theoretical results revealed that hybrid Poplar-Beech CLT had more tremendous potential for structural bending performance in the construction and building sector.
... During the global commercialization of CLT, attempts have been made to manufacture CLT using local softwood [5][6][7][8], hardwood [9][10][11][12][13][14], and a combination of the two [15][16][17]. Composite CLTs (CCLTs) made from structural composite lumber (e.g., laminated strand lumber, laminated veneer lumber, and oriented strand lumber) and dimension lumber have also received considerable attention [18][19][20][21][22]. The general purpose of using local wood species for CLT manufacturing was to enhance the added value of local timber resources [23] and reduce the costs and carbon emissions caused by long-distance transportation of raw materials [24]. ...
Article
During the global industrialization process of manufacturing cross-laminated timber (CLT), attempts have been made to use local wood species. For areas rich in bamboo resources but relatively short in timber resources, the use of bamboo- and wood-based composites to manufacture composite CLT (CCLT) has great potential. In the present work, two new types of 3-ply CCLT panel structures constituting bamboo woven panel and hem-fir lumber were investigated. In the major and minor strength directions, flatwise bending and shear tests were conducted to investigate their failure modes, maximum bending moment, bending stiffness, modulus of elasticity (MOE), bending strength, interlaminar shear strength, and specific bending and shear performance. Moreover, 3-ply hem-fir glued-laminated timber and CLT were used as controls. The effective MOE of each panel structure was calculated according to shear analogy theory and modified gamma theory and then was compared to the measured MOE. Based on the shear analogy theory, the effect of the thickness of layers on the MOE of the panels was investigated. Results showed that unlike other types of CCLT, the new CCLT exhibited distinct plate-like orthogonal strength characteristics. Its theoretical MOE agreed well with the measured MOE as the accuracy changed with the panel structure. By changing the panel structure of the new CCLT, if the MOE of one strength direction was reduced, the MOE in the other strength direction could increase accordingly based on the layer characteristics. The results presented in this paper can provide a guidance for future design and optimization of bamboo-wood CCLT.
... Flores et al. [16] studied the shear properties of CLT panels through actual experiments and simulated shortspan flexural tests. The planar shear test is another approach to evaluate the shear resistance of the CLT [17,18], which is considered as the most appropriate one in Europe [19]. However, the result in one study indicated that the planar shear test and the short-span bending test provide comparable data [20]. ...
Article
The objective of this study is to examine the mechanical performance of cross laminated timber (CLT) panels made of low-value sugar maple under out of plane loads through mechanical tests and numerical simulation. The laminations were sorted into High and Low classes based on the measured modulus of elasticity (MOE). Two 3-layer sugar maple CLT layups as High-Low-High and Low-High-Low glued with resorcinol-based adhesive and one CLT layup of High-Low-High glued with melamine-based adhesive were prepared. Block shear, long-span bending (span-to-depth ratio of 33:1) and short-span bending (5.5:1) tests were conducted to evaluate the bonding, flexural and shear behavior of these low-value sugar maple CLTs. With a limited sample size, the lab-manufactured low-value sugar maple CLT provided a 50% to 80% higher MOE and at least two times higher MOR than CLT type E1 from APA/PRG 320. Similar MOE and MOR improvements were found by comparing CLT made with other species from literatures. The finite element simulation of bending tests was conducted with the orthogonal constitutive law and the progressive damage model based on the calibrated material properties parameters from lumber rating and references. The simulation results on each CLT panel type have a reasonable comparison with experimental test data. Therefore, these integrated experiment and simulation methods can provide detailed mechanical behaviors of the low-value sugar maple CLT, which can also be applied to other CLT species and layup.
... Moreover, rolling shear cracks occurred between the annual growth rings in the middle layer due to the transverse orientation of the intermediate layer in specimens ( Fig. 7(b)). Numerous research studies have found low wood strength in rolling shear stress [1,22,28,29,30,31]. ...
Article
With the expansion of cross-laminated timber (CLT) material throughout the global construction community, an effort is being made to explore the use of regionally produced CLT materials from Iran, including the testing of fast-grown, hand-planted poplar (Populus alba). This paper investigated the out-of-plane bending properties of CLT panels manufactured using poplar at various span-to-depth ratios (SDR). Mechanical properties of poplar CLTs investigated included the modulus of rupture, apparent modulus of elasticity, effective bending stiffness, effective shear stiffness, and maximum shear stress in both the major and minor directions. Experimental test results were compared with both the shear analogy model and finite element method (FEM) results to examine the use of predictive modeling. Bending properties were predicted using the shear analogy method and FEM compared well with experimental results, with the FEM able to predict the distribution of bending and shear stress across the beam thickness. Modulus of rupture and apparent modulus of elasticity increased with increasing SDR in both the major and minor strength directions. In the major strength direction, the effective modulus of elasticity and maximum shear strength values predicted by the shear analogy method were in good agreement with experimental results. As noted in previous studies, the effective shear stiffness predicted by the shear analogy method in the major strength direction was 510% less than that of experimental results.
... Furthermore, the high shear strain zones also were found around pith and alone glue lines, where were the failure locations. The failure mechanism of rolling shear, observed by DIC in this study, is in agreement with the results in other studies [5,10,26]. ...
... It was found that 3 layer panels made from SPFs had a rolling shear strength of 2.03 MPa, while three-layer hybrid panels with LSL in the core layer had a significantly greater shear strength of 2.96 MPa. In contrast, Wang et al. [16] observed a reduction in bending strength for three-layer CLT panels when laminated veneer lumber (LVL) was used in the transverse, core layer, with a primary failure corresponding to shear along the LVL glue line. ...
Article
The effect of gaps between boards in transverse layers of cross-laminated timber (CLT) on shear strength was investigated. Five-ply specimens with gaps of 0, 6, 89 and 178 mm were subjected to short-span three-point bending tests. Digital imaging correlation (DIC) was used to quantify strains and displacements in core layers. Panel shear capacity met the requirements of the PRG 320 standard for performance-rated CLT for the gap sizes tested, suggesting that small gaps do not reduce shear strength enough to warrant consideration in design. DIC data and Timoshenko beam theory were used to estimate rolling shear modulus and specimen deflections, which agreed well with measured values.
... Their findings revealed that the rolling shear strength of three-layer SPF panels produced under 0.4 MPa of pressure was 2.22 MPa, which was higher than the 1.85 MPa result achieved under 0.1 MPa of pressure, suggesting that higher manufacturing pressure produces stronger panels, resulting in higher shear strength. More recently, researchers developed a modified method with reference to ASTM D2718 (ASTM 2011) to measure the rolling shear properties of cross layers using the three-layer CLT specimens (Gong et al. 2015;Wang et al. 2017). ...
Article
Shear properties of the cross layer in cross laminated timber (CLT) panels are critical for design purposes, especially for applications with high concentrated loads and low span-to-depth ratios. Understanding how the shear properties of CLT lamstock vary with respect to fiber orientation-from perpendicular-to-grain (90°) to parallel-to-grain (0°)-can lead to new and innovative panel layups with superior shear performance. In this study, two-plate shear specimens (per the relevant standard) were fabricated with fiber orientations of 0°, 30°, 45°,60°, and 90°with respect to the shear load direction using eastern hemlock 2 × 4 lumber. Both shear modulus and shear strength were measured as a function of fiber orientation. The influence of fiber orientation and the interaction of resisting components on the shear properties are discussed concerning observations of the types of failure modes. The results indicate that the effective shear stiffness (GA eff) and the characteristic shear strength (F v) for a traditional (90°) CLT panel made from eastern hemlock would satisfy grade E3 CLT per the relevant standard. Moreover, the shear strength of the angled cross layers with 30°and 45°fiber orientation with respect to the major panel axis would be 98% and 59% higher, respectively, than CLT with a 90°cross layer orientation.
... Most of these phenomena are expressed in the by-support area. [12,13] The analysis of the works shows that the testing of standard samples does not provide an adequate picture of the nature of the distribution of forces in the body of the structure. Full-scale testing of elements has a high cost and complexity, which entails a rise in design cost. ...
Article
Full-text available
Since ancient times, wooden structures have been used by man for the construction of buildings and facilities. For many centuries, the structural elements of buildings and facilities made of wood have been the main ones, and still have broad prospects for use in modern capital construction, as they have sufficient high strength and stiffness, are reliable and durable, while having a small mounting weight. In particular, a number of Western countries are already erecting high-rise buildings using a framework of laminated wood constructions. The indisputable advantage of wooden structures is environmental friendliness. However, with all the harmony of the wood structure, its tracheid’s are not standard, which is the main reason for the variability of its mechanical properties. With alteration of a cross-section of flexural member, the nature of the load distribution, as well as the nature of the fracture, changes. An additional factor that affecting the force distribution is the nature of the reinforcement and methods of the reinforcement fixing methods. The methods used to calculate the “low” reinforced beams often give a large error in the calculation of “high” beams. In the work, a rational methodology for calculating wooden glued reinforced beams with symmetrical reinforcement is determined.
... This suggested that Japanese Larch as perpendicular layers could significantly improve the rolling shear modulus compared to SPF and Spruce. Wang et al. investigated into the improvement in the rolling shear strength by using composite structure material or modified fast-growing poplar as the perpendicular layer [32]. Gu and Pang calculated the rolling shear strength of southern Pine CLT with different adhesives, which ranged from 1.69 MPa to 2.43 MPa [33]. ...
Article
Full-text available
Japanese larch is one of the main plantation tree species in China. A lack of engineered wood products made by Japanese larch , limits its application in wood structures. In this study, based on optimum process parameters, such as pressure (1.2 MPa), adhesive spread rate (200 g/m2) and adhesive (one component polyurethane), the mechanical properties of Japanese larch made cross laminated timber ( with different lay ups were evaluated by means of the static method . Results of this study show ed that variations in lay ups significantly affected the mechanical properties of CLT. The strength and modulus of bending and parallel compression for CLT increased with the thickness of lumber while that o f bending, parallel compression and rolling shear all decreased with the number of layers. Thickness, layup orientation and the number of layers all had an impact on the strength of CLT. Failure modes obtained from numerical simulation w ere basically the same as those of experimental test s . There was also strong alignment between theoretical value and test value for effective bending stiffness and shear stiffness. Thus, the shear analogy method can be used to predict the mechanical properties of CLT effectively. This study proved great potential in using Japanese larch wood for manufacturing CLT due to its good mechanical properties.
... Liu and Lam [3] carried out an experimental investigation on the coupling effect of shear and tension on angle brackets in the NSERC project. In the China NSFC project, Wang et al. [4] tested the planar shear properties of hybrid CLT fabricated with lumber and laminated verneer lumber (LVL) used as shear walls; Shu et al. [5] investigated the rotational performance of bolted joints with slotted-in steel plates used as CLT-to-steel connections. For the CLT shear wall structural system, the mechanical performance of full-scale CLT structures was tested by Yasumura et al. [6] under the reversed cyclic lateral loads, and one three-dimensional structural model was also developed. ...
Article
This paper presents the performance-based seismic assessment framework on conventional CLT shear wall structures (C-CLTStrs) and post-tensioned CLT shear wall structures (PT-CLTStrs). Numerical models of both the conventional CLT shear walls and the PT CLT shear walls were developed and calibrated with experimental results. A direct displacement-based design (DDD) procedure was then developed and demonstrated by the design examples of one 8-storey C-CLTStr and a set of 8-, 12-, and 16-storey PT-CLTStrs. Corresponding simplified structural models were developed. A series of pushover and time-history dynamic analysis was conducted afterwards to calibrate the calculated structural performance objectives with the design targets of the DDD procedure. Finally, using 50 mainshock (MS) and 50 mainshock-aftershock (MSAS) earthquake records, probability seismic demanding analysis (PSDA) were conducted to evaluate two engineering demanding parameters of the structures, namely the maximum inter-storey drift (MaxISDR) and the residual inter-storey drift (ResISDR). The MaxISDR limit states of the PT-CLTStrs are recommended at 0.7%, 1.4%, and 2.2% for the immediate occupancy (IO), life safety (LS), and collapse prevention (CP) hazard levels, respectively. The MaxISDR of the PT-CLTStrs is almost twice that of the C-CLTStrs, while the ResISDR is at most 50% of that of the C-CLTStrs. The damage probability of the 8-storey PT-CLTStr indicated by ResISDR is not significantly sensitive to the consideration of aftershocks seismic input, whereas, when aftershocks are considered, up to a 7.0% difference under the LS hazard level is caused in the damage probability of the 8-storey C-CLTStr indicated by ResISDR.
... Engineered wood products such as Cross Laminated Timber (CLT) and Laminated Veneer Lumber (LVL) as well as hybrid mass timber panels [1] have gained popularity in the last few decades in the construction of tall timber buildings [2][3][4]. If located in an earthquakeprone area, these buildings have to withstand not only vertical gravity loads but also horizontal loads such as wind loads and seismic loading [5]. ...
... It was interrupted by few or several steps along the wood rays (in the radial direction) and following the load transfer plates when reaching them (Fig. 18a). These observations agree well with descriptions by Wang et al. [60]. In European ash specimens, the only ring porous hardwood species investigated in this study, rolling shear failure propagated within only one annual ring until reaching the load transfer plates (Fig. 18b). ...
Article
Shear stresses in planes perpendicular to the grain, so-called rolling shear stresses, need to be considered in the ultimate and serviceability limit state design of many timber structural elements. Knowledge about the rolling shear modulus and strength has further gained in importance since the invention and increased use of cross laminated timber (CLT). As a result of the orthogonal orientation of adjacent layers within CLT, rolling shear stresses develop when CLT is subjected to out-of-plane bending. Previous numerical and experimental studies on rolling shear are largely restricted to Norway spruce (Picea abies (L.) Karst.). In the present study, experimental investigations on the rolling shear properties were carried out on six timber species. The two investigated coniferous species were Norway spruce (Picea abies (L.) Karst.) and pine (Pinus sylvestris L.). Four deciduous species, namely European beech (Fagus sylvatica L.), European ash (Fraxinus excelsior L.), poplar (Populus tremula L.), and European birch (Betula pendula R.) were investigated. Furthermore, different board geometries and sawing patterns were investigated. In comparison to Norway spruce, all other investigated species featured higher rolling shear properties. In particular, these of European beech and European ash were roughly three-times higher. In agreement with previous findings, the aspect ratio (board width vs. board thickness) as well as sawing pattern were identified as main influencing parameters on the rolling shear properties. In addition to single board segments, multi-segment systems were experimentally tested and numerically investigated. Parallel systems consisting of either two or four board segments were tested to obtain information on potential system effects of laminations within single CLT cross layers regarding rolling shear strength and rolling shear modulus, i.e. stresses may be distributed depending on the local stiffness. This system effect may influence the shear strength, the shear modulus, and the failure behaviour compared to the results of single segment testing. Often, CLT elements consist of more than one cross layer. Layups can also feature parallel layers, however, usually with grain in direction of the main span direction. Some of these layups have a remarkable potential for two-dimensional load transfer. Thus, these commonly double or triple layers are exposed to rolling shear by stresses in the weak load transfer direction. As rolling shear failure of one of the cross layers in layups featuring alternating orthogonal layers as well as layups featuring some parallel layers leads to the ultimate failure of the entire element, such elements can be considered as serial systems with regard to the rolling shear strength and rolling shear modulus. In order to investigate the serial-parallel system behaviour, multi-segment systems consisting of 4 × 3 board segments were tested. The investigated systems should allow linking the results obtained from single element testing to the actual behaviour of CLT laminations and, subsequently, to give recommendations for rolling shear test configurations as well as related rolling shear properties. The outcomes show a good comparability between the results from out-of-plane bending tests on CLT elements featuring rolling shear failures and EN 408-alike shear tests conducted on board segments. The analysis of the within- and between-boards variation of rolling shear properties and density is also a part of this paper. The results of this study provide an overview of the rolling shear properties of tested European softwood and hardwood species. The investigated species are already in use, or have a significant potential to be used for construction purposes in the near future. The findings regarding the influential material- and product-related parameters contribute to a better understanding of the mechanical behaviour of timber subjected to rolling shear.
... This feature leads to large-scale components and enables fast construction (Chen, 2011). Researchers (Sikora et al., 2016;Li, 2017;Wang et al., 2017) investigated the structural properties of CLT and standards for CLT (ANSI/APA, 2012;EN 16351, 2014;FPInnovations, 2011) were recently published. They provide the technical information relating to CLT products which were manufactured by a gluing process. ...
Article
In this study, the bending behavior of cross-laminated timber (CLT) connected by nails were investigated. Especially, the load-carrying capacity of the nail-jointed CLT under out-of-plane bending was predicted by the lateral resistance of the used nails. Three-layer nail-jointed CLT specimens and a nail connection were manufactured by 30 mm (thickness) × 100 mm (width) domestic species (Pinus koraiensis) laminas and ∅3.15 × 82 mm nails using a nail-gun. Shear test for evaluating the nail lateral resistance and bending test for evaluating the load-carrying capacity of the nail-jointed CLT under out-of-plane bending were carried out. As a result, two lateral resistance of the used nail, the 5% fastener offset value and the maximum value, were 913 N and 1,534 N, respectively. The predicted load-carrying capacity of the nail-jointed CLT by the 5% offset nail lateral resistance was similar to the yield points on the actual load-displacement curve of the nail-jointed CLT specimens. Meanwhile, the nail-jointed CLT specimens were not failed until the tension failure of the bottom laminas occurred beyond the maximum lateral resistance of the nails. Thus, the measured maximum load carrying capacities of the nail-jointed CLT specimens, approximately 12,865 N, were higher than the predicted values, 7,986 N, by the maximum nail lateral resistance. This indicates that the predicted load-carrying capacity can be used for designing a structural unit such as floor, wall and roof able to support vertical loads in a viewpoint of predicting the actual capacities more safely.
Article
Bamboo is one of the most important renewable resources in China, leading to the development of bamboo products as well. Alternative applications of bamboo need to be developed in the field of construction, especially in cross-laminated timber (CLT) construction, due to better mechanical performance of bamboo and the increasing popularity of CLT construction in recent years. The bonding performance of cross-laminated timber-bamboo (CLTB) composites fabricated with Spruce-pine-fir (SPF) dimension lumber and bamboo scrimber boards was investigated here. L9 (3⁴) orthogonal experiments with four factors (adhesive type, adhesive spreading rate, clamping pressure, and clamping time) and three levels were applied to evaluate their impacts on the bonding indicators of CLTB through block shear and delamination tests. Results showed that adhesive type had the most critical influence on the bonding performance. The optimal manufacturing parameters were adhesive of phenol resorcinol formaldehyde (PRF), adhesive spreading rate of 250 g/m², clamping pressure of 1.0 MPa, and clamping time of 420 min, respectively. PRF adhesive yielded higher block shear strength, wood failure percentage, and lower rate of delamination than one-component polyurethane (PUR) and emulsion polymer isocyanate (EPI), especially under wet or boiling condition.
Article
In order to better understand, and ultimately improve, the interlaminar shear performance of CLT, this paper explores the influence of three different laminates—larch, poplar and OSB—as transverse layers on the interlaminar shear performance of CLT. The results showed that, although larch, poplar and OSB have little difference in overall density, the interlaminar shear strength of CLT was significantly affected with the use of each as the transverse layer. The interlaminar shear strength in the major direction of CLT prepared with three different materials as transverse layers is: 4.18 MPa (Larch - Poplar - Larch), 3.52 MPa (Larch - Larch - Larch) and 2.71 MPa (Larch - OSB - Larch). The interlaminar shear strength in the minor direction of CLT prepared with three different transverse layers is: 0.91 MPa (Larch - Poplar - Larch), 1.11 MPa (Larch - Larch - Larch) and 0.22 MPa (Larch - OSB - Larch). The interlaminar shear failure modes of the three CLT specimens are different: in the major strength direction, when larch was used as the transverse layer, the interlaminar shear failure mode was rolling shear failure of the transverse layer. When poplar was used as the transverse layer, the interlaminar shear failure modes of CLT were transverse layer shear failure and surface layer shear failure. When OSB was used as a transverse layer, the interlaminar shear failure mode of CLT was the internal shear failure of OSB. In the minor strength direction, the interlaminar shear failure mode of each of the three CLT specimens starts from the unsized gap on the side of the bottom laminate element, and the typical bending failure mode occurs in the transverse layer. CLT prepared with poplar as the transverse layer has lower density, but better interlaminar shear performance in the major strength direction. The interlaminar shear strength in the strong axial direction is affected by the structure of the transverse laminates, and as such homogeneous laminates are more suitable for use as transverse laminates.
Article
The load-displacement curves of six types of roof-to-wall connection joints were obtained through uplift experiments, while the mechanical properties of each type of joint were compared and analyzed, and the applicability of each joint was verified by the Foschi load-displacement curve model simulation. The specimens were made of three kinds of wood (Pinus sylvestris (PS), Spruce-Pine-Fir (SPF), and Douglas fir (DF)) and two different metal connectors (A-type and B-type), and then the monotonic pullout tests were conducted on each specimen. The failure modes of each group of specimens were analyzed, and the characteristic values analysis method was used to analyze and compare the characteristic values of the load-displacement curves of each specimen, including six characteristic values: maximum load, yield load, deformation capacity, energy dissipation capacity, ductility ratio, and initial stiffness. The results showed that the load capacity of TA group (specimens with A-type metal connectors) was much greater than that of TB group (specimens with B-type metal connectors). The specimens made of DF had the best mechanical performance, but the specimens of DF group were prone to brittle failure. Finally, the fitting parameters of the Foschi model applicable to such joints were obtained.
Article
In this study, the bending performance of a separable cross-laminated timber (CLT)–concrete composite slab for reducing environmental impact was investigated. The slab has consisted of CLT and eco–concrete, and round-notch shape shear connectors resist the shear force between the CLT and eco-concrete. The eco–concrete was composed of a high-sulfated calcium silicate (HSCS) cement, which ensures low energy consumption in the production process. The bending stiffness and load-carrying capacities of the slab were theoretically predicted based on the shear properties of the notch connectors and validated with an experimental test. The shear properties of two types of notch shear connectors (Ø100 mm and Ø200 mm) were measured by planar shear tests. As a result, the stochastically predicted bending stiffness of the slab (with Ø100 mm shear connector) was 0.364 × 10¹² N mm², which was almost similar to test data. The load-carrying capacities of the slab were governed by the shear failure of the notch connectors, and the lower fifth percentile point estimate (5% PE) was 21.9 kN, which was 7.9% higher than the prediction (20.2 kN). In a parameter study, the effect of notch diameter for the CLT-concrete slab span was analyzed depending on the applied loads, and the maximum spans of the slab with Ø100 mm notch or Ø200 mm notch were not significantly different.
Article
Cross-laminated timber (CLT) as one novel engineered massive wood is prone to the rolling shear failure, due to its configuration characteristics of orthogonal orientation of adjacent layers. For comprehending its rolling shear behavior and clarifying the influence of the lamination aspect ratios on the rolling shear strength, pseudo-static monotonic rolling shear tests were conducted on the CLT specimens with aspect ratios ranging from 2.54 to 9.40, based on a modified planar shear test method. Their rolling shear strength or rolling shear resisting capacity was calculated with respect to the influence of the aspect ratios. The damage modes of the rolling shear specimens were analyzed considering the influence of their lamination width. The effect of the lamination width and that of the lamination thickness on the rolling shear strength were investigated, respectively. Besides, in the case of different aspect ratios, the strength modification factor defined as the ratio between the design rolling shear strength to the design parallel-to-grain shear strength of the outermost laminations was provided, which can facilitate the estimation of the rolling shear strength. Considering the influence of the aspect ratios, both the regression equations of the strength modification factor and the predictive equations of the rolling shear strength were proposed. It is found that a highly positive linear correlation exists between the rolling shear resisting capacity and the aspect ratio. The damage modes of the CLT rolling shear specimens depend on their lamination width; besides, when the lamination width increases from 184 to 235 mm, little improvement can be identified for the rolling shear resisting capacity. Meanwhile, larger thickness of the CLT transverse laminations can result in less CLT rolling shear strength. Overall, the proposed equations are capable of predicting the rolling shear strength of CLT fabricated with the SPF lumber. The study can contribute to the comprehension on the CLT rolling shear behaviors and provide reference values for mitigating the possibilities of CLT rolling shear damages in engineering design.
Article
A novel flattened bamboo-wood composite cross-laminated timber (CCLT) made from flattened bamboo and hemlock lumber was developed, and its mechanical performance was investigated and quantified in this work. The results demonstrated that the CCLT columns and control hemlock CLT counterparts had nearly equal axial compression strength, but the CCLT yielded a higher compression modulus of elasticity (MOE). Additionally, the CCLT compression behaviors were not significantly affected by the height. Compared with hemlock CLT, the CCLT exhibited a slightly higher flatwise bending MOE and strength in the major strength direction. Furthermore, the MOE and strength of the CCLT under edgewise bending were 17.3% less and 16.2% greater than those under flatwise bending, respectively. The load-carrying capacity of the CCLT was mainly governed by the interfacial failure between the bamboo and wood, in which no rolling shear failure was observed. Those features are unique for the new CCLT for engineered applications.
Article
This current research work was aimed to develop an innovative panel by combining the nail-laminated timber (NLT) and cross-laminated timber (CLT) into a single product named nail-cross-laminated timber (NCLT) to take advantage of both structural panel products in a single product as a structural member. To investigate the mechanical properties of the NCLT, its bending performance and rolling shear were examined and compared to those of conventional CLT and NLT floor panels. The NCLT and the CLT panels were fabricated in 3 layers such as the CLT. Polyurethane adhesive was used on the laminations. The cross layers of the NCLT were made of a 30-mm-thick vertically laminated NLT. The NLT floor panels were fabricated by vertically nailing the laminations using a zigzag nailing pattern. Results showed no significant differences in the bending strength properties of the three panel types. Both CLT and NCLT showed a comparable rolling shear strength, however, the rolling shear failure in the NCLT was much more ductile than that of the CLT. Overall, the NCLT panels indicated an appropriate short-term bending and rolling shear performances.
Thesis
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The growing demand for sustainable materials makes wood to have great potential for its use in construction. Cross Laminated Timber (CLT) is an engineered wood product consisting of wood boards arranged in orthogonally cross-linked layers and is mainly used as a plate or sheet structure. In Brazil, CLT panels are produced industrially using reforestation wood of Pinus taeda species. As the physical and mechanical wood properties depend on several natural factors, knowing the structural performance of CLT boards produced with nationally grown wood is important. This study analyzes the structural performance of CLT plates by experimental tests and numerical simulations. The main experimental tests were conducted with 21 plates composed of five layers of boards, totaling 16 cm in thickness, and submitted to four-point bending, according to BS EN 16351:2015. Pinus taeda samples were extracted from tested plates that were later analyzed by simple bending, according to NBR 7190:1997, and by perpendicular compression and parallel compression to the grain, according to BS EN 408:2010 to explore the properties of the raw material. Numerical analysis of static and vibration mode performance ware carried out by RF-LAMINATE and RF-DYNAM Pro modules of the commercial software RFEM 5, using composite plate elements and determining mesh discretization by the Grid Convergence Index method. Such simulations considered Mindlin and Kirchhoff plate theory, as well as normative resistance classes according to NBR 7190:1997 and BS EN 338:2016. Physical and mechanical properties were obtained from experimental tests, such as specific gravity, moisture, bending strength and stiffness, as well as shear strength and stiffness of CLT plates. The CLT´s bending strength was associated with the tensile strength of finger joints on the lower layers, while ruptures due to shear stress occurred due to the deficiency of strength capacity of rolling shear in the transverse layers of the CLT. When plate theories and different normative characterization were evaluated in numerical simulation, results of strength and stiffness with relevant variations were found, some of which are not admissible. The difference between adhesive weights from 220 to 250 g/m2 was statistically evaluated and no significant difference was observed regarding the stiffness and strength of the samples. It was also possible to estimate acceptable loads as a function of the length of CLT plates, being analytically and numerically, verified that the natural vibration is one of the critical factors that limits CLT design length. Finally, this research is a result of the partnership between university and industry, which allowed conducting experimental tests of structural size for characterization of CLT plates and predicting their static structural behavior and vibration modes through analytical and numerical simulations, expanding the technical knowledge on CLT industrially produced with raw material planted in the national territory.
Article
Plantation softwood is the future timber material resource for building and construction. However, significant volumes of sawn softwood are considered out-of-grade and sold at a loss. New approaches and methods need to be implemented to value-add out-of-grade timber and increase structural yield from existing plantations. This paper provides a critical review of out-of-grade characteristics of pine timber to gain an understanding of the strengths and weaknesses of this resource as a structural building material. Methods to incorporate out-of-grade timber into current building systems are presented and building technologies that can facilitate this use are identified. Finally, it discusses developments and important considerations for design of cross laminated timber (CLT) as a prime example of a building system with good capacity to incorporate high volumes of out-of-grade timber. This provides critical information for the maximum utilisation of sawn out-of-grade pine and is anticipated to create new opportunities that can effectively incorporate this renewable and sustainable material resource into innovative building systems and technologies.
Article
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The insulated predictions were carried out for LVL, CLT and HCLT in order to evaluate their sound properties, in which the theoretical value of sound insulation was predicted by regarding the substances in wood cell wall as equivalence to specific medium based on Biot model, and the wood anatomical characteristics, such as the length and diameter of tracheid, diameter of pit, and porosity, were taken into account for determining the equivalent density and bulk modulus of elasticity of wood cell wall. By comparing the tested and predicted values of sound insulation, the conclusion were drawn as follows: the predicted values of sound insulation were significantly correlated with the tested values for LVL, CLT and HCLT. As for Masson pine and Southern pine, the adjacent of earlywood and latewood was considered as sandwich structure for the calculation of sound insulation. Meanwhile, the bonding interface was creatively introduced to improve the accuracy of sound insulation prediction. The transfer function involved in sound insulation prediction provide an effective method to characterize the sound insulation volume of wood composite in construction and decoration areas.
Article
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This work investigated the feasibility of manufacturing composite cross-laminated timber (CCLT) from bamboo and a western hemlock and amabilis fir mix (hem-fir). Bamboo parallel strand lumber (bamboo PSL) was first fabricated as the surface laminae of CCLT. No. 2 and Btr 2×6 western hem-fir dimension lumber was imported from British Columbia (BC), Canada. The lumber was then sorted and further dried to form the inner laminae of CCLT. Multiple 800 × 800-mm CLT billets were fabricated using a commercial single-component polyurethane (PUR) adhesive. Block shear and delamination tests were conducted to examine the bond quality and durability of bamboo-wood CCLT. The results demonstrated that it is technically feasible to manufacture bamboo-wood CCLT with acceptable bond quality (shear strength, wood failure percentage, etc.) and delamination. Further studies should focus on the optimization of process parameters for manufacturing and surface treatment to improve the bond quality and durability and quantify the mechanical performance of bamboo-wood CCLT with a full-size production trial.
Conference Paper
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The feasibility of using poplar (Populus euramericana cv. I-214) as cross layer to fabricate cross-laminated timber (CLT) was examined in this study. For comparison purpose, Douglas fir (Pseudotsuga menziesii) and Monterey pine (Pinus radiata D.Don) were used as well to produce five layups of CLT panels. The mechanical properties tested included the bending strength in the major direction, modulus of elasticity in the major direction, shear strength parallel to the major direction and shear strength perpendicular to the major direction. It was found that the mechanical properties of CLT panels containing poplar were similar to those made of non-poplar wood. The major failure modes found were joint failure, shear failure and delamination. It could be feasible to use poplar as a cross layer to fabricate CLT without decreasing its strength properties.
Article
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Hybrid cross laminated timber (HCLT) was fabricated using lumber and/or laminated strand lumber (LSL), the mechanical performances of which were evaluated. To reach this goal, the mechanical properties of LSL and the bending properties of CLT and HCLT were measured in this study. The properties of LSL measured included the tension strength (only in the major direction), shear strength, shear modulus, and modulus of elasticity (MOE) and modulus of rupture (MOR). The failure mode of each kind of specimens was visually examined and recorded. Four types of CLT panels, one generic CLT (used as control) and three types HCLT were fabricated. The properties measured included the bending properties (in the major direction) and planar shear properties (in both major and minor directions). It was found that the HCLT had better bending and planar shear properties than that of generic CLT. The MOE and MOR of HCLT having LSL as the outer layers were 19% and 36% higher than those of generic one, respectively. The MOE and MOR of HCLT having LSL as core layer (replacing the cross lumber layer) were 13% and 24% higher than that of generic CLT, respectively. The failure modes of four types of CLT observed included the planar shear failure of cross lumber layer, tension failure of bottom LSL, and tension failure of bottom lumber, especially tension failure of lumber originated at a knot(s).
Conference Paper
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Since wood products for structural elements, such as cross-laminated timber (CLT), have gained importance in the building sector, the need for appropriate and reliable design codes has become essential. For this reason, this work focuses on global failure mechanisms and the corresponding evolution of different crack modes in CLT plates, depending on geometric and/or material related influence quantities. Therefore, plate-bending experiments on 3-and 5-layered CLT-plates were carried out. In addition to standard evaluation methods, each specimen were cut into cubes (10/10/10 cm) to get information about the failure modes inside the plates. Areas and location of dominant shear failure, tensile failure, delamination, and mixed failure modes could be clearly defined and connected to geometry and loading situation. Based on this evaluation well known but not yet in detail described effects, such as the ductile structural behavior of CLT plates, can be explained.
Conference Paper
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Cross-laminated timber (CLT) is a panel-shaped engineered wood product, assembled of layers of lamellas (mostly softwood) with perpendicular orientation of the grain direction. In contrast to other panel-shaped engineered wood products, CLT is not used as components of structural elements, but rather as load bearing plates and shear panels. The design of CLT used as load-bearing plates is often governed by serviceability criterions like maximal deflection and vibration susceptibility. Hence, predicting the respective behaviour of such panels requires accurate information about their elastic properties. With the aim of determining the global elastic properties of full-scale CLT panels directly in the production line, a fully automatic, non-destructive procedure based on experimental and theoretical modal analysis was developed: Resonance frequencies and mode-shapes of the plates are determined first by means of an experimental modal analysis. A simulation model based on Reddy's higher order plate theory is then used to analytically calculate natural frequencies and mode shapes as functions of the unknown elastic parameters. Finally, in an optimization process two in plane moduli of elasticity and three shear moduli can be identified by minimizing the differences between measured and analytically estimated resonance frequencies. First, the method was investigated in the laboratory. The applicability of the method was then proven on 42 CLT panels with different dimensions, layer sizes and from different producers, and validated by static bending experiments on full-scale panels and panel-bars. Finally the procedure was optimized for the application in the production line.
Article
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Wood-based panels represent an important category of composites consisting of natural raw materials and one or more synthetic products. They are available in a wide range of types and thus can satisfy the most frequent needs and functions of the building trades. In light of renewed interest in the structural uses of these materials, an adequate mechanical characterization is necessary to designers who require reliable information for structural analysis. In this context, an extensive research program has been developed at the University of Trento, Italy to characterize Poplar plywood. These testing methodologies, which adhere to the new European Standards, along with some preliminary results are briefly analyzed and presented herein. Les panneaux à base de bois constituent une catégorie importante de matériaux composites, faits à partir d'une matière première naturelle et d'un ou de plusieurs produits de synthèse. Une gamme étendue de ces panneaux est actuellement disponible pour répondre aux usages les plus courants de la construction. Étant donné l'intérêt renouvelé pour l'utilisation de ces matériaux, une caractérisation mécanique est nécessaire pour fournir des informations fiables aux bureaux d'études. Un vaste programme de recherche a été entrepris à l'Université de Trento afin de caractériser les propriétés mécaniques du contreplaque de peuplier, utilisant des méthodes d'essai en accord avec les nouvelles normes européennes. Quelques résultats préliminaires sont brièvement présentés et discutés dans cet article.
Article
Rolling shear properties of cross-laminated timber (CLT) are very low because of the configuration of the cross layer. In some applications, they are the key properties that govern the design and application of CLT. To explore an appropriate method for assessing the rolling shear properties of CLT, variable span bending tests and two-plate shear tests were conducted. Three types of down-scaled black spruce (Picea mariana) specimens, including wooden cross layer (WCL), steel-wood-steel (SWS), and three-layer down-scaled CLT (wood-wood-wood [WWW]), were fabricated using onecomponent polyurethane (for edge gluing) and epoxy adhesive (for steel and wood bonding). Deflection of a WWW specimen was predicted using a shear analogy method based on rolling shear modulus (Grt) of the cross layer obtained from the variable span bending test and two-plate shear test methods and was then compared with the deflection directly measured on WWW specimens. The test results showed that rolling shear modulus of WCL from the two-plate shear test was 72.61 MPa, which was more than twice that of the cross layer of SWS from the variable span bending test. Rolling shear strength of WWW measured using the three-point bending method was 2.74 MPa at a span-to-depth ratio of 6.
Chapter
From the point of view of economics, a defect in wood is any feature that lowers its value on the market. It may be an abnormality that decreases the strength of the wood or a characteristic that limits its use for a particular purpose. There is a certain amount of risk involved in classifying an abnormality as a defect because what is judged to be definitely unsuitable for one application may prove to be ideal for a different or special use.
Article
Cross-laminated timber (CLT) is a growing phenomenon and a recent building solution alternative in timber construction in North America by using massive or solid wood plates as roof, floor, and wall elements. In this paper a variation of the conventional CLT is considered by studying the performance of box-based CLT systems, which refer to box beams with multiple voids. In some loading situations, such as out-of-plane bending, these systems, which can reduce structural weight without significant loss of strength or stiffness, may be structurally efficient and cost competitive. Comprehensive three-dimensional finite-element models, which can be used to analyze the mechanical behavior of such box structures, were developed. Four prototype layups, each having five replicates, were designed, manufactured in-house, and tested under symmetric four-point bending (also known as third-point loadings). The numerical analysis agreed well with experimental data in terms of vertical deflection and flexural rigidity. This paper contributes to the understanding of the structural performance of box-based CLT systems for the commercial and residential applications.
Article
The design and application of cross laminated timber (CLT) is strongly influenced by the rolling shear properties of cross layers. Hence, to predict the performance of CLT requires accurate information about its rolling shear properties. In this study, a wooden cross layer (WCL) specimen was made of 38 mm by 89 mm black spruce lumber of a grade of No. 3. The average rolling shear modulus of the WCL specimens measured by the two-plate shear test was 136 MPa. The rolling shear modulus measured was then used as input to predict, using the shear analogy method, the deflection (dc) of a 3-layer CLT beam subjected to the centre-point bending load. Subsequently, the bending test was conducted to directly obtain the deflection (dm) of a 3-layer CLT beam for validation. It was found that dc could, with an adjustment factor (α), provide a good estimate of dm at different span-to-depth ratios under the centre-point bending test. Additionally, the bending test results showed that the specimen width did not have a statistically significant effect on apparent modulus of elasticity (Eapp) and apparent shear modulus (Gapp) of 3-layer CLT beam specimens.
Article
Shearing is an essential deformation in the treatment of mechanical pulp fibers into a papermaking pulp. Knowledge of the contribution of shear to the fiber treatment during processing can be obtained by measurements on fibers in the form of wood. In this work, an attempt was made to use the Iosipescu method for testing wood in rolling shear. Despite the small size of the shear region of interest between notches made in the wood, the results and their dispersion in both the elastic and inelastic ranges were in accordance with previous results found using other testing methods. The stress-strain relationship was analysed in relation to the specimen's density profiles in the region of interest. Differences in density explained up to 50% of the inter-specimen variability in the shear modulus and in the inelastic behavior. Failure occurred outside the shearing zone in a large number of specimens. Thus the configuration chosen was not adapted to provide for the strength of wood in rolling shear. This behavior limited the amplitude of the strain that could be reached between the notches.
Article
The mechanical properties and characteristic values of radiata pine plywood for structural use were measured using the European standards (EN 789 and EN 1058). Eight different compositions of panels with thicknesses from 9 to 30 mm were tested. Their mechanical properties were found to be similar to those of other plywoods from Europe manufactured with spruce. The test results of plywood showed the mechanical properties of layers (basic values) using the method proposed by European standards. The strength and elasticity modulus of the layers were obtained for bending, tension and compression. It can be concluded that basic values are suitable for estimating the properties of different compositions of plywood.
Influence of rolling shear modulus on strength and stiffness of structural bonded timber elements
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Failure modes of CLT/HCLT in bending tests (a) Group A, (b) Group B and (c) Group C
  • Fig
Fig. 5. Failure modes of CLT/HCLT in bending tests (a) Group A, (b) Group B and (c) Group C.
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