Volume 4 Issue 1
Jan.  2019
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Cross-laminated Timber (CLT) in China: A State-of-the-Art

  • 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.
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  • [1]

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    Tafreshi K T, Winter W, Pixner T, 2008. Development of earthquake bracing systems for multi-storey buildings using slender shear wall elements in cross-laminated timber (CLT). In: WCTE 2008-World Conference on Timber Engineering, Miyazaki, Japan.

    Wang B, 2014. Experimental study on flexural behavior of orthogonal laminated wood based on fast-growing poplar. Nanjing, China: Nanjing Technology University.

    Wang B J, Wei P X, Gao Z Z et al., 2018. The evaluation of panel bond quality and durability of hem-fir cross-laminated timber (CLT). European Journal of Wood and Wood Products, 76(3): 833–841. DOI: 10.1007/s00107-017-1283-7.

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    Wang Z Z, 2017. Effect of macroscopic characteristics of sawn timber on rolling shear properties of cross layer of CLT. Nanjing, China: Nanjing Forestry University.

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Cross-laminated Timber (CLT) in China: A State-of-the-Art

    Corresponding author: BradJianhe WANG, bradwang@shaw.ca
    Corresponding author: Peixing WEI, wayne0448123@163.com
  • 1. College of Civil Engineering, Nanjing Forestry University, Nanjing 210037, China
  • 2. Ningbo Sino-Canada Low-Carbon Technology Research Institute, Ninghai 315600, China
  • 3. School of Landscape Architecture, Jiangsu Vocational College of Agriculture and Forestry, Jurong 212400, China

Abstract: 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.

1.   Development of Cross-laminated Timber (CLT)
  • In the early 20th century, the building materials' market was largely occupied by reinforced concrete (Brandner et al., 2016). However, over the past decade or so, timber has recaptured market shares and there has been a tendency to replace mineral-based building materials. An important reason for this regain in market share is the commercial launch of new engineered wood products as mass timber products (MTPs) (Schickhofer et al., 2010). At present, the MTPs including cross-laminated timber (CLT), glued-laminated timber (glulam), nailed-laminated timber (NLT), and structural composite lumber (SCL) are increasingly used for building applications. They can be prefabricated with precise dimensions and openings in a factory, thereby allowing for a faster erection and minimal construction waste (Zhou et al., 2017).

    The CLT is one kind of prefabricated the MTP. It consists of at least three layers of structural lumber boards or the SCL stacked crosswise at an angle (typically at 90°) and glued or stapled together (Chen, 2011; Gagnon and Pirvu, 2011) (Fig. 1a, 1b). The CLT has the advantages of high prefabrication rate, convenient transportation and fast installation, and low damage to the site environment. Thus, it is considered as the best substitute for traditional building materials (Zhang et al., 2017). The crosswise layup method of the CLT makes it possible to fully use the material characteristics of the high tensile strength of the wood in the direction of the grain and the high compressive strength in the transverse direction. To meet the special need of the CLT application, double-layer lumber boards can be placed parallel-to-grain direction to obtain superior mechanical properties in the direction of the grain. In addition, Canadian scientists proposed a box- based CLT system for achieving more diverse and complex structural purpose (Fig. 1c) (Chen, 2011). This system effectively reduced the self-weight of the CLT panel on the basis of ensuring a certain bearing capacity, and became more cost effective.

    Figure 1.  Different structures of CLT panels

    The concept of the CLT was developed in Austria in the 1970s and 1980s and the first modern CLT mill was established in Europe in the late 1980s. In 1993, the first CLT building was erected in Switzerland (Que et al., 2017). In the past 10 years, Austria, Germany and Italy have carried out lots of researched on the CLT (Tafreshi et al., 2008; Brandner, 2013; Helene and Schickhofer, 2013; Rinaldin et al., 2013). While this product is well- established in Europe, Canada, the United States, New Zealand, and Japan, etc., lots of related research work have also been carried out, which greatly promoted the applications of the CLT (Buchanan et al., 2008; Chen et al., 2008; Chen, 2009; Ceccotti et al., 2013; Pei et al., 2013; Hindman and Bouldin, 2015). The CLT can be widely used as wall, roof and floor panels, and also as a main body structure or decks for a bridge (Schubert et al., 2010).

    In addition to research on the performance and applications of the CLT, several countries promoted the product standardization. The Canadian version and the US version of the CLT Handbook were respectively published (Gagnon and Pirvu, 2011; Karacabeyli and Douglas, 2013), which provided the technical guidance for the manufacturing, structure design and construction of the CLT and also laid a foundation for the revision of the relevant standards. The North American CLT product standard was published in 2012 (ANSI/APA PRG 320-2012, Standard for Performance-rated Cross-laminated Timber, American National Standard Institute, USA) and revised in 2018 (ANSI/APA PRG 320-2018). Wood Design Standards Committee of American Wood Council renewed the National Design Code for Timber Buildings (ANSI/AWC NDS- 2015) with inclusion of the the CLT. The UK Standards Policy and Strategy Committee issued "BS EN 16351-2015" in 2015, established complete and systematic requirements for the CLT. Subsequent revision of the CLT standards and specifications has effectively promoted the applications of the CLT.

    The CLT has recently become more and more popular in building applications in Europe and the United States. The building height has been continuously uplifted and structural form has become more diversely. In 2009, The Stadthaus, a 9-storey CLT wooden mixed-use apartment in Hackney, London, was completed (Fig. 2a) (Xiong et al., 2016). The CLT was used in the superstructure of Stadthaus's wall, core tube, floor slab, etc. to provide the vertical bearing capacity and lateral resistance of the structure. In 2012, Forte, a 10-storey apartment in the Port of Asia Victoria, Melbourne, Australia (Fig. 2b), with the shear wall of the CLT, was the first CLT wood building over the world. In 2014, the 14-storey treet building in Bergen, Norway was completed (Fig. 2c), using a beam-column frame-support structure. The CLT panels were used for integrated prefabricated room units, and also used for walls, corridors, elevator shafts and balconies of the building (Malo et al., 2016).

    Figure 2.  Famous tall wood buildings

    An 18-story student residence with a frame-core tube system, Brock Commons, was located at the campus of The University of British Columbia (Fast et al., 2016). The core tube was cast-in-place using reinforced concrete. The first floor of the building was concrete frame structure. For the 2nd to the 18th floors, the CLT panels were adopted as the horizontal force-bearing members and the glulam columns as the vertical force-bearing members, and they were connected by steel members (Fig. 2d).

    Studies on performance and engineering applications of the CLT have reached a high level abroad, but the relevant studies of the CLT in China were still in an infancy (Zhang et al., 2017). Currently, research institutes such as Ningbo Sino-Canada Low-Carbon Technology Research Institute (SCLC), Tongji University (Tongji), University of Science & Technology of Beijing (USTB), Chang'an University (CHD), Nanjing Forestry University (NFU), Nanjing Technology University (NTech), Beijing Forestry University (BFU), and Chinese Academy of Forestry (CAF) have conducted some studies on the CLT including process parameter optimization, basic mechanical tests and numerical simulation. This work reviewed the recent research of the CLT and discussed the development trend of the CLT in China.

2.   Recent Research of CLT in China
  • At this stage, only a few institutes and universities have conducted some research of the CLT in China concentrating on process optimization, basic panel performance, and use of local species for the CLT manufacturing. And some valuable results were obtained.

    In conformation with the North American CLT standard, Prof. Wang from SCLC led his team to build the China's first CLT pilot production line, and subsequently developed the world's first large-scale prefabricated CLT panel made from Canadian western hemlock lumber (https://mp.weixin.qq.com/s?__biz=MjM5NTg5NDI4Mg==&mid=2651228420&idx=1&sn=027306c8724ef5c02e24d4238efd33d9#rd). Wang et al. (2018) prepared Canadian western hemlock CLT using two types of adhesive and two levels of applied pressure. The results of block shear and delamination test showed that the type of adhesive and the level of applied pressure had a significant effect on the bond quality, wood failure and durability of the CLT. Other team members made the full-scale hemlock CLT panel and systematically evaluated and analyzed the basic mechanical properties in major strength direction and durability of the CLT (Wang Y L et al., 2017; Li M M et al., 2018; Lu Y et al., 2018a; Xie et al., 2018). The interlaminar shear strength of the hemlock CLT made in the SCLC was measured using a short-span three-point bending method with a span-to-depth ratio of 6 to validate the theory. The cooperative research team from Tongji University conducted a study on the flatwise bending and compressive performance of the Canadian hemlock CLT and obtained the mechanical properties of the hemlock CLT in the major strength and minor strength directions through the test, which provided the basic data for the engineering applications of hemlock CLT (He et al., 2018)

    Based on the CLT pilot production line of the SCLC, the CAF used domestic Japanese larch lumber to make the CLT and tested its bending performance, inter-laminar shear performance, rolling shear performance, and compressive performance (Gong et al., 2018a; Gong et al., 2018b; Gong et al., 2018c; Gong et al., 2018d). They also explored the influence of process, lumber modulus of elasticity, assembly direction, lumber thickness and number of layer on its mechanical properties (Gong et al., 2018a; 2018b; 2018c; 2018d). Thus, for the domestic Japanese larch, the key process parameters and basic mechanical performance of the CLT were successfully established for engineered applications.

    The research team from South China Agricultural University (SCAU) studied the feasibility of using the fast-growing small-diameter eucalyptus wood to make the CLT and optimization of relevant process parameters (Liao et al., 2017; Lu Z H et al., 2018). The results of eucalyptus CLT bending and shear tests proved that the CLT had acceptable mechanical properties.

    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., 2014; 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. Jiang (2016) studied mechanical properties of the CLT made from Chinese fir with different thickness and analyzed its failure modes.

    To compare some above-mentioned domestic R & D teams' research (Wang et al., 2016; Liao et al., 2017; Gong et al., 2018a; Gong et al., 2018b; Lu Y et al., 2018b; Xie et al., 2018), bending and shear performance of the CLT made from different wood species are listed in Table 1 and Table 2. It should be note that the size of the CLT has a neglectable effect on its mechanical performance. However, the data referred to different publications still has to some extent value to discuss with the same span-depth ratio, especially for the CLT with large difference of mechanical properties resulting in the relative reduce of size effect. As shown in Table 1, eucalyptus is one of the representational tree species in China. The small-diameter eucalyptus CLT had a higher modulus of elasticity (MOE) but lower flexural strength. And its flexural strength was much lower than that of the softwood (Canadian western hemlock and Japanese larch) CLT. Composite the CLT, Douglas fir LVL as core layer, had a lower MOE and flexural strength than hybrid CLT made from SPF lumber. While taking Douglas fir LVL as the surface layers of composite CLT, its MOE and MOR increased about 29% and 17%, respectively. According to Table 2, the shear strength of small-diameter eucalyptus CLT was lower than that of the softwood (Canadian western hemlock and Japanese larch) CLT and composite CLT. Spruce-Pine-Fir (SPF) was a mixture of three wood species, commonly used for the CLT manufacturing in North America. Obviously, the mechanical properties of the CLT made from Canadian western hemlock and domestic Japanese larch were comparable to and even superior to SPF CLT.

    CLT type Specimen dimension (mm) Span-depth ratio MOE (MPa) MOR (MPa)
    Canadian western hemlock CLT 3150×305×105 30.0 10 668–11 966 34.78–41.51
    Domestic Japanese larch CLT 2700×305×75 30.0 10 340–16 760 40.52–59.76
    Small-diameter eucalyptus CLT 1820×305×54 30.0 11 466 (Mean) 24.5 (mean)
    Hybrid CLT (SPF-SPF-SPF) 2000×89×114 16.4 7908 (Mean) 28.6 (mean)
    Composite CLT (SPF-LVL*-SPF) 2000×89×114 16.4 7222 (Mean) 25.7 (mean)
    Composite CLT (LVL*-SPF-LVL*) 2000×89×114 16.4 9299 (Mean) 30.1 (mean)
    *Note: LVL was made from Douglas fir veneer.

    Table 1.  Bending properties of CLT

    CLT type Specimen dimension (mm) Span-depth ratio Inter-laminar shear strength (MPa)
    Canadian western hemlock CLT 735×305×105 6 1.88–2.23
    Domestic Japanese larch CLT 510×305×75 6 2.28–2.84
    Small-diameter eucalyptus CLT 400×150×54 6 1.30 (mean)
    Composite CLT (SPF-SPF-SPF) 610×305×114 5 2.25 (mean)
    Composite CLT (SPF-LVL-SPF) 610×305×114 5 2.11 (mean)
    Composite CLT (LVL-SPF-LVL) 610×305×114 5 2.40 (mean)

    Table 2.  Inter-laminar shear properties of CLT

    Wang (2014) used poplar and Douglas fir as raw materials to prepare evenly layered and homogeneous CLT panels and evenly layered and hybrid CLT panels. By the test of three- and five-layer CLT panels, an optimization design method based on strength was proposed. In addition, Mao (2015) studied the in-plane mechanical properties (ultimate bearing capacity and in-plane equivalent stiffness) of seven groups of 21 CLT wall members, and the results showed that the in-plane performance of the CLT panel was mainly in the elastic stage and the failure was generally brittle.

    Fu (2012) of the CHD analyzed the bending and dynamic performance of the CLT bridge deck through experiment, and discussed the influence of number of layer and connection mode on the mechanical performance of the CLT bridge deck.

  • Domestic scholars had also carried out the relevant research on the connection performance of the CLT members. Sun et al. (2018) revised the hysteresis curve of finite element simulation based on the node and wall test of the CLT structure, and developed a finite element model of the CLT structural node and wall. The numerical simulation method was also applied to analyze the influence of damper parameters on the energy consumption of the shear wall system for the pre-stressed shear CLT wall system and the dual effects of pre-tension on the energy dissipation and self-reset (Hu and He, 2018).

    Dong et al. (2018) selected self-tapping screws to connect the CLT. Through the monotonic loading and gradual loading tests of the connected test pieces, the results revealed that increasing the length and diameter of the self-tapping screws can significantly improve the shear capacity of the CLT connected pieces and when the nailing angle was 45°, and the shear bearing capacity achieved its maximum. 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).

    Zhang (2015) conducted a study on the integrity and energy dissipation capacity of steel-wood buckling restraint support. It was found that the CLT structure had a good ability to restrain the steel tube. Therefore, the design method and flow of steel-wood buckling restraint support was presented.

    The research on the seismic performance of semi- rigid connections of the CLT was carried out by USTB. It was found that the failure of all fasteners was pulled out as the ideal ductile failure mode, and the hysteresis curve showed high nonlinearity and degradation of stiffness and strength and pinching phenomenon (Shen et al., 2015). Based on three flexible joint tests of CLT, the team used OpenSees to simulate the high nonlinearity, degradation of strength and stiffness and pinching and then carried out damage analysis of the CLT connection (Shen et al., 2016). And they also numerically studied the mechanical performance of steel-frame and CLT infill wall structure under the monotonous and cyclic loading. The effect of cooperative performance between the CLT wall and the steel frame and number of connections on overall structure was analyzed (Shen et al., 2017).

    Considering the characteristics of the structure and section of the wood bridge deck, Gao (2010) proposed a new bridge deck system based on the combination of the CLT panel and steel beam. They found that the number of layer and the connection method will affect the CLT bridge deck. Jia et al. (2018), from BFU, conducted a study on the shear performance of the T-connector at the CLT wall-floor joint. The connectors were able to withstand the shear force of the wall-slab joints and the CLT wall showed good stiffness.

  • Owing to the incompleteness of China's specifications and the public's lack of awareness of multi- and high-rise wood buildings, the CLT were predominantly used in low-rise buildings in China, and those buildings were mainly built for demonstration purpose.

    In March 2014, a two-storey wood construction building with a hybrid light-frame and the CLT structure in China was reported for demonstration in Qian'an City, Hebei Province (Fig. 3a). And its CLT materials were manufactured by Qian'an City Big Tree Industry Co., Ltd., which was the first producer of the CLT in China (Chen et al., 2018). In the same year, the 5-storey CLT wood construction building, the first multi-storey CLT building in Asia, located in Taiwan Province, China was completed. In this building, the architects made full use of the CLT's good cantilever performance, and set the cantilevered balcony on the second, third and fourth floors (Fig. 3b1). In addition, the CLT was left exposed inside the building, which largely reflected the natural features of wood construction (Fig. 3b2) (Strobel, 2016).

    Figure 3.  The CLT wood construction buildings in China. (a) CLT wood construction building in Qian'an, Hebei; (b) CLT wood construction building in Taiwan; (c) OTTO Café in Ninghai, Zhejiang; (d) All-ecological CLT demonstration house in Ninghai, Zhejiang

    Figure 3c shows the China's first public CLT demonstration building (OTTO Café), which was jointly built by SCLC and Tongji University (Xiong et al., 2018). All CLT panels were prefabricated. The prefabrication method made the OTTO Café simple and convenient to build meeting the requirements of green, low-carbon, energy saving, environmental protection and sustainability. Cooperating with Portugal Amerin Group, SCLC successfully applied the insulated cork board as insulation and cladding to build China's first two-storey ecological CLT house (Fig. 3d). Note that the OTTO Café and the all-ecological CLT demonstration house (Fig. 3d) were demolished and reconstructed after one year and it took only three days to dissemble and reassemble, which fully reflected the flexibility and adaptability of the CLT buildings. Therefore, those types of the CLT buildings can be widely applied for China's tourism real estate, urbanization and rural industrialization.

    In addition, Zhongyi Scientech Timber Structure Co., Ltd., one manufacturer of the CLT located in Shandong Province, also carried out some engineering applications of the CLT. The business building of the Binzhou Administrative Center was one case, which was designed to use composite CLT elements combined with wooden beams and columns.

  • Cross-Laminated Timber (LY/T3039- 2018), a National Forestry and Grassland Administration forestry industry standard, completed by SCAU and SCLC etc., was officially released at the end of 2018 and will be officially implemented in May 2019. Although the newly promulgated Standard for design of timber structures (GB 50005-2017) and Technical standard for multi-story and high rise timber buildings (GB/T 51226-2017) provided specifications for the CLT component design and connector design, etc., The construction and acceptance specifications have not yet been completed (Li Z et al., 2018; Liu and Yang, 2019). Especially, at present, the lack of regulations in the area of fire prevention and building inspection resulted in some obstacles for promoting the residential and non-residential CLT buildings.

3.   Research on Bamboo-wood Composite CLT in China
  • Wood construction has broad prospects in China, but it should be noted that the conflict between domestic timber supply and demand was very prominent (Zhang, 2001; Yu and Yu, 2013). Currently, a majority of dimension lumber used for the CLT in China needs to be imported. Thus, high transportation cost and tariff affected the popularization of the CLT. Although the imported lumber from the international market can alleviate the current problem of wood supply and demand, excessive dependence on imported lumber is not conducive to the development of China's wood construction industry. Therefore, finding the new materials for the CLT manufacturing is essential.

    Su and Zhang (1995) proposed that bamboo- wood composite structure is an effective way to utilize bamboo resources. Both bamboo and wood are anisotropic materials. Bamboo has the characteristics of high strength, good wear resistance and high toughness and wood has the characteristics of high rigidity, large strength-to- weight ratio and convenient to process. Thus, the use of bamboo and wood to produce bamboo-wood composite CLT can give full play to their own material advantages. And it can also help alleviate the current situation of domestic tight wood supply and promote the commercialization of the CLT.

    Bamboo-wood composite CLT, if reasonably designed using bamboo-based materials and wood-based materials, should be an innovative engineered composite product with Chinese characteristics and high strength and aesthetic values. Several Chinese patents of such products have been jointly issued or applied by NFU and SCLC (Zhang et al., 2010; Wei and Wang, 2019).

  • As shown in Fig. 4, the bamboo-wood composite CLT can be divided into two categories. Using bamboo-based materials as the longitudinal layer of the CLT and wood based materials as the transverse layer (Fig. 4a) was first been thought to obtain bamboo-wood composite CLT with good toughness. To improve the rolling shear strength of the transverse layer, bamboo-based materials can be used for the transverse layer of the CLT panel, and wood-based materials for the longitudinal layer in the other structure (Fig. 4b). Herein, wood-based materials should include oriented strand board (OSB), plywood and the LVL and other SCL and bamboo-based materials should comprise bamboo-mat plywood, bamboo curtain plywood and bamboo-wood-mat plywood, laminated bamboo lumber, reconstituted bamboo (or bamboo scrimber), and other engineered bamboo materials.

    Figure 4.  Typical structure of bamboo-wood composite CLT

    The above two types of bamboo-wood composite CLT are only the basic three-layer CLT panel structure. The main structure parameters include number of layers, layer composition and position, and so on. In addition to the above, the structure of bamboo-wood composite CLT could have other variations. For example, it can be nailed for element assembly, or be assembled with different layer angles, and even box-type of panel structure.

    The SCLC is the first institute in China working on the development of bamboo-wood composite CLT products. Those products have been tested for bonding durability and bending and compression performance, and are ready for commercialization. A portion of those research results have been published (Wei et al., 2019). In this work, bamboo parallel strand lumber was selected as the surface layers of composite CLT (the same structure as Fig. 4a). The average inter-laminar shear strength of bamboo- wood composite CLT was 2.38 MPa, which was almost the same as that of hem-fir CLT according to the previous work (Wang et al., 2018). Under dry condition, block shear strength and wood failure percentage of bamboo-wood composite CLT were respectively 2.07 MPa and 70.6%, which were lower than that of hem-fir CLT. Under vacuum pressure soak/dry (VPD) conditions, block shear strength and wood failure percentage of bamboo-wood composite CLT were respectively 1.12 MPa and 78.7%, which were also lower than that of hem-fir CLT. Using PUR adhesive, the average delamination rate of bamboo-wood composite CLT was 6.8%. Thus, bamboo-wood composite CLT had better bond durability than hem-fir CLT.

  • Bamboo-wood composite CLT is an innovative engineered wood product with Chinese characteristics, but there are some problems that need to be resolved. For example, bamboo-based materials and wood-based materials were so different that poor bond between bamboo and wood could present. Also, the production process of bamboo-wood composite CLT panel is quite different from the generic wood CLT, thus, the key manufacturing parameters such as glue selection, glue application rate, applied pressure, pressing time, etc., need to be systematically studied. Further, the performance of the bamboo-wood composite CLT needs to be thoroughly studied, and a product standard needs to be developed for engineered applications. Theoretically, work is also needed to validate whether the commonly used CLT theories such as Mechanically Jointed Beams Theory, Shear Analogy Theory, K method and other CLT calculation theories based on beam theory are applicable to the mechanical modelling and calculation of bamboo-wood composite CLT.

4.   Conclusion and Outlook
  • As a new type of green building material, the CLT has attracted widespread attention at home and abroad. Developing CLT with Chinese characteristics and promoting CLT or hybrid CLT buildings can help reduce carbon emission and save energy consumption, thus it has important economic, social and ecological benefits. The authors believed that the development of the CLT in China had broad prospects based on the following reasons:

    (1) China has a large population and less land, which is a bottleneck in the development of wood construction building. According to Standard for design of timber structures (GB 50005-2017), the height of wood construction building should not exceed three stories. However, the CLT makes the high-rise wood building possible, which will be more suitable for China.

    (2) The CLT is a new generation green and low-carbon building material suited for prefabricated buildings. There is a big push in China toward off-site construction. Two standards have been officially published in 2017 related to prefab wood constructions.

    (3) China lacks timber but has abundant bamboo resources. Bamboo-wood composite CLT should exhibit light-weight and high-strength performance, which is of significance to promote the development of bamboo or wood prefabricated buildings in China. Wood has higher stiffness and bamboo has better strength. The two materials should be reasonably combined for high-performance and low-cost. It is technically feasible to manufacture bamboo-wood composite CLT using the same process as wood CLT. Further test is needed to investigate the performance-rated bamboo-hemlock CLT. At the same time, we should improve the relevant wood theory of composite CLT as soon as possible, and establish its product standard.

    Currently, the cost of wood constructions in China is much higher than that built with steel and concrete. Thus, adopting the hybrid structure of the CLT and steel or concrete for high-rise building, or using the hybrid structure of light wood frame and the CLT, is a potential solution. Note that the CLT, as a new material, is still in its infancy in China. Therefore, further research is deemed necessary to better understand its performance and establish its standard for product promotion and commercialization.

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