Hybrid Cross-laminated Timber Research Articles

Face bonding strength of cross laminated northern hardwoods and softwoods lumber

Producing cross-laminated timber (CLT) has opened a new market for the lumber industry in North America, while few hardwood species have been studied in the U.S. for CLT production. Combining hardwood species in mixed hardwood CLT or in hybrid CLT can be a solution to boost the market of the undervalued hardwoods. However, the knowledge gap on bonding hardwoods needs to be filled to provide evidence of feasibility. This study focused on the face bonding properties of the cross laminations made of seven hardwood species and two softwood species from the Great Lakes region using two commercial structural adhesives, the phenol resorcinol adhesive (the Resorcinol) and the melamine urea formaldehyde adhesive (the Melamine). A total of 45 combinations of the selected species were studied for the bonding strength (shear under compression) and the percentage of wood failure. For single species samples, the bond strength was positively related to the specific gravity of wood and the bond strength of hardwoods was 33% and 82% stronger than that of softwoods bonded with the Resorcinol and the Melamine respectively. The mixed hardwoods showed higher bonding strength (the Melamine: 5.45 MPa, the Resorcinol: 5.28 MPa) than mixed softwoods (the Melamine: 2.8 MPa and the Resorcinol: 2.7 MPa). Among the Resorcinol bonded mixed combinations, 54% had a percentage of wood failure less than 80%, while the Melamine bonded had only 4 out of 22 which had a percentage of wood failure less than 80%. The overall bonding strength of the hybrid combinations was 5% weaker than that of the mixed hardwoods. All hybrid combinations bonded with the Melamine met the 80% wood failure criterium, but some bonded with the Resorcinol had a percentage of wood failure less than 80%. Anatomical features, especially pore distribution, played a key role in the bonding performance. However, the Melamine adhesive consistently achieved over 80% wood failure across all pore distribution types.

Experimental and machine learning study on a novel high-performance hybrid steel-grout connector for cross-laminated timber panels under pre-yield cyclic loads

This work presents the results from quasi-static cyclic tests on a novel hybrid steel-grout connector for cross-laminated timber (CLT) panels. These test series are part of an experimental, analytical, and numerical research program to develop reliable and resilient connections for hybrid CLT mass timber structural assemblies. Each designated connector arrangement’s cyclic loading step path has been anchored to the yield point; this latter was obtained as the average of the seven replicates of monotonic tests. From the cyclic test results, mechanical characteristics, namely, the secant stiffness and the residual slip, have been evaluated and discussed. Furthermore, machine learning (ML) models based on deep neural networks have been developed to predict the mechanical characteristics of connectors in the function of the mechanical and geometrical properties of each material used. The developed ML models proved to be able to predict the connector’s stiffness and residual slip and were used to infer the effects of experimental variables on these performance parameters. It was shown that the steel rod and grout diameters are the most influencing parameters regarding the secant stiffness of connectors. As for the residual slip, it was found that the grout diameter and the steel rod strength class are the most influencing parameters. Furthermore, it was observed that a grout-to-rod diameter ratio of about 3.6 enables maximization of the secant stiffness while minimizing the residual slip. Lastly, polynomial equations were developed and found to be able to predict the secant stiffness and residual slip of connectors with a coefficient of determination of 0.99 and 0.98, respectively.

Evaluation of the bonding process and interlaminar shear properties of hybrid cross-laminated timber prepared with larch and OSB

Evaluation of the bonding process and interlaminar shear properties of hybrid cross-laminated timber prepared with larch and OSB

The Bending Properties of Hybrid Cross-Laminated Timber (CLT) Using Various Species Combinations.

Cross-laminated timber (CLT) has become a massive commercial success in recent years due to its high performance, technological advantages, and low environmental impact. The finite softwood raw material supply has motivated researchers to find alternatives. This study presents an investigation of the viability of some Hungarian hardwood materials, such as CLT materials. Homogeneous beech, poplar, and spruce panels, as well as their combinations, were created using a polyurethane adhesive. The experimental results show the clear potential of Hungarian poplar, which performed much better than spruce. Poplar's modulus of elasticity (MOE) and modulus of rupture (MOR) values reached or exceeded those of high-grade commercial softwood CLT. The bending properties of beech and hybrid beech-poplar panels far exceeded the performance of commercial panels, which shows the excellent potential of high-density hardwoods for high-performance CLT production. Beech-spruce hybrid panels seriously underperformed. This was caused by gluing issues, probably due to the large density differences between the two species, as evidenced by the glueline failure exhibited by most of these specimens during testing. The average panel density proved to be the best predictor of mechanical performance, except for beech-spruce hybrid panels.

Mechanical properties of hybrid cross-laminated timber with wood-based materials

In this study, four wood-based materials (plywood, laminated veneer board (LVB), oriented strand board (OSB), and particle board (PB)) were proposed as layered materials for CLT to improve its shear performance. The fabricated hybrid CLT exhibited better bending, shear performance, and compressive strength than that of traditional CLT. The out-of-plane bending performance, in terms of modulus of elasticity and modulus of rupture, improved by 2912–5836 MPa and 1.89–18.54 MPa compared with that of traditional CLT. The out-of-plane shear modulus and strength of the LVB CLT and PLY CLT improved by 31.19–76.15 MPa and 0.5 MPa, respectively, compared with that of traditional CLT. The compressive strength of the hybrid CLT improved by 6.86–24.6 MPa. The cross-arranged veneer with the LVB and plywood exhibited rolling shear failure. The ratio of tensile and shear failure of LVB CLT and PLY CLT increased compared to traditional CLT. The failure mode of the hybrid CLT with OSB and PB exhibited shear failure in the middle of the panel thickness of the OSB and PB. This study confirmed an improvement in the mechanical properties of hybrid CLTs with wood-based materials. LVB and plywood hybrid CLTs exhibited the best results. Additional studies are required on the mechanical properties of hybrid CLTs in the arrangement direction of wood-based materials and in the minor direction of the hybrid CLT.

Behaviour of hybrid cross laminated timber in compression perpendicular to grain in different layup structure, support conditions, and loading configurations

Cross laminated timber (CLT) is recognized as alternative to traditional construction materials. As a floor member, it causes the compressive deformation or even damage perpendicular to the grain of CLT due to vertical load imposed by the column or wall. The challenge is how to improve the compressive strength (fc,90) and elastic modulus (Ec,90) perpendicular to the grain under the high diversity of possible load configurations. Compared with normal CLT, hybrid CLT (HCLT) used structural composite materials (e.g. laminated strand lumber) instead of timber, which had more homogeneous mechanical properties. In this study, the spruce-pine-fir (SPF) and laminated strand lumber (LSL) were used to prepare HCLT. The full surface loading, point loading representing columns and line loading representing walls of HCLT in the perpendicular to grain direction were carried out. The results show that fc,90 increased with increasing thickness ratio of LSL in the total thickness of HCLT under full surface loading, the highest increase in strength of HCLT reached 35.71 %, data of Ec,90 had the opposite conclusion. In the case of point loading, the fc,90 and Ec,90 under discretely support was lower than those under successively support. Load configuration had significant influence on the fc,90 and Ec,90 including middle position (M), corner position (C), edge parallel (E) and edge vertical (V) to the grain of the outer layer. In the case of line loading, it was in good agreement with point loading results, and fc,90 and Ec,90 under line loading were lower than that under point loading. The failure modes were mainly the cracks along the wood ray direction of SPF material, while no obvious damage for LSL under full surface loading. In addition, the failure modes mainly of local loading included the shear failure for SPF material, fiber fracture failure of LSL material and the adhesive layer cracking in the non-directly compression zone.

Influence of Puspa Wood and Coconut Trunk Combination on the Characteristics of Cross-Laminated Timber Bonded with Polyurethane Adhesive

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. Keywords: Coconut trunk, cross-laminated timber, layer combination, polyurethane adhesive, puspa wood

구조용 목재의 축열성능 향상을 위한 상변화물질/바이오차 적용 복합 교차집성재 개발

In this study, phase change materials (PCM) was applied to the core-layer of cross-laminated timber (CLT) to improve the low thermal storage performance of CLT. To solve the phase leakage of PCM, PCM/biochar composites were prepared in a vacuum state by impregnating PCM (n-heptadecane) in biochars that were pyrolyzed at 400 and 500 °C, respectively. Gypsum boards with improved thermal storage performance was prepared by mixing 10 wt% of the prepared PCM/biochar composites, and these were applied to the core-layer of the CLT to develop a hybrid CLT. The physical and chemical properties of PCM/biochar composite were evaluated through FT-IR, SEM, TGA, and DSC analysis, and the thermal performance of P/B board and hybrid CLT was evaluated through heat transfer experiments. The surface temperature reduction and heat transfer delay effect of hybrid CLT to which biochar produced at a pyrolysis temperature of 400 °C was applied was excellent.

Study on the interlaminar shear properties of hybrid cross-laminated timber (HCLT) prepared with larch, poplar and OSB

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.

Comparative life cycle assessment of a reinforced concrete residential building with equivalent cross laminated timber alternatives in China

With the development of mass timber, cross laminated timber (CLT) has gradually become a sustainable alternative to conventional building materials to alleviate the increasing energy consumption and carbon emissions by the building sector. This study aims to explore the life cycle greenhouse gas emissions (LCGHGE) and life cycle primary energy (LCPE) of three high-rise residential buildings in the cold region of China through a life cycle assessment approach. The three buildings are conventional reinforced concrete (RC), CLT and hybrid CLT buildings. The results show that CLT and hybrid CLT buildings produce 15.00% and 10.77% lower LCGHGE, respectively, compared to the RC building within a 50-year service life. A clear difference in greenhouse gas (GHG) emissions and primary energy (PE) in the product and construction stages is visible, with 46.52% and 37.24% of embodied GHG emissions reduced in CLT and hybrid CLT buildings, respectively, compared to the RC building. In the operational stage, RC building has lower PE and GHG emissions to CLT alternatives. The thermal mass effect has led to a 2.25% and 2.12% PE increase for space heating and cooling in CLT and hybrid CLT buildings, respectively, compared to the RC building. For the End-of-Life (EoL) stage, CLT demonstrates great recycling potential and biomass residues. The sensitivity analysis shows that the design of the low U-value of the building envelope and high-efficiency energy systems has a significant relationship with energy reduction during the operational phase of the three buildings, magnifying the impacts of the initial and EoL stages. • CLT and hybrid CLT buildings produce 15.00% and 10.77% less LCGHGE than RC buildings in Tianjin, China, respectively. • Mass timber construction shows great advantages over RC buildings in the P&C/EoL stage. • The operational GHG emissions and PE of CLT and hybrid CLT buildings were 12–13% higher than those of the RC building. • Energy-efficient methods can enhance the LCA performance of hybrid CLT building.

Study of Properties and Mechanism of Bonding Line in Three-Layer Hybrid Cross-Laminated Timber

The physical and chemical properties of three kinds of laminations relative to the bonding properties of three-layer hybrid cross-laminated timber (CLT) were studied. The density of the parallel layer lamination of CLT was 640.47±61.85 kg/m3, and the perpendicular layer laminations for CLT larch wood, poplar, and oriented strand board (OSB) were 392.51±40.14, 343.73±17.16, and 384.41±12.93 kg/m3. Block shear bond strength (BBS), wood failure percentage (WFP), and delamination rate (DR) of the hybrid CLT specimens were also determined. The results showed that the three kinds of hybrid CLT prepared with polyurethane (PUR) adhesive had good bonding properties under 1.2 MPa of bonding pressure. The BBS values of CLT with larch wood, poplar hybrid, and OSB hybrid were 2.32, 2.41, and 1.98 MPa, respectively; furthermore, their WFPs were all greater than 80%, and their DRs were 9.32%, 0.37%, and 0.11%, respectively. Regarding the relationship between perpendicular layer material properties and bonding properties, analysis revealed that delamination performance was strongly correlated with pH, buffer capacity, and the surface free energy of the perpendicular layer, whereas the WFP and BBS values had a strong correlation with pH and buffer capacity. Density was determined to be unrelated to bonding performance in the CLT prepared in this experiment. Microscopic analysis of the bonding line proves that the PUR adhesive can effectively penetrate into three different laminations under a bonding pressure of 1.2 MPa and form enough nails to ensure bonding strength.

The Dimensional Stability and Bonding Performance of Hybrid CLT Fabricated with Lumber and COSB

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.

Pristup projektiranja ekonomičnih hibridnih CLT podova

There is a growing research and production interest for the application of lower-cost hybrid cross-laminated timber (CLT) panels composed of timber layers of dissimilar quality. Therefore, an approach for the design of cost-effective hybrid CLT panels in bending, based on the existing analytical and novel finite element procedures, is presented in the paper. The gamma-method, the extended gamma method, and the composite theory are applied in the analysis of square panels, while the finite element model based on the Reddy’s full layerwise theory is used for the complex-shape panels in bending. An extensive benchmark technical and economic study is performed for 25 CLT panels, considering various spans, lamination schemes, geometries, and boundary conditions. Cost savings made by using a lower timber class in central zones of CLT panels are highlighted and quantified. This concept shows an economic potential that should be considered during the design and production of CLT panels in structural engineering applications, such as lightweight floor structures.

Low-cycle fatigue life and duration-of-load effect for hybrid CLT fabricated from lumber and OSB

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.

Structural performance of hybrid Poplar-Beech cross-laminated-timber (CLT)

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.

Research Trends in Hybrid Cross-Laminated Timber (CLT) to Enhance the Rolling Shear Strength of CLT

In this study, hybrid CLT research and development trends were analyzed to improve the low rolling shear strength of CLT, a large wooden panel used in high-rise wooden buildings. Through this, basic data that can be used in research and development directions for localization of CLT were prepared. As a way to improve the low rolling shear strength, the use of hardwood lamina, the change of the lamina arrangement angle, and the use of structural composite materials are mainly used. Rolling shear strength and shear modulus of hardwood lamina are more than twice as high as softwood lamina. It confirmed that hardwoods can be used and unused species can be used. Rolling shear strength 1.5 times, shear modulus 8.3 times, bending stiffness 4.1 times improved according to the change of the layer arrangement angle, and the CLT strength was confirmed by reducing the layer arrangement angle. Structural wood-based materials have been improved by up to 1.35 times MOR, 1.5 times MOE, and 1.59 times rolling shear strength when used as laminas. Block shear strength between the layer materials was also secured by 7.0 N/mm2,which is the standard for block shear strength. Through the results of previous studies, it was confirmed that the strength performance was improved when a structural wood based materials having a flexural performance of MOE 7.0 GPa and MOR 40.0 MPa or more was used. This was determined based on the strength of layered materials in structural wood-based materials. The optimal method for improving rolling shear strength is judged to be the most advantageous application of structural wood based materials with strength values according to existing specifications. However, additional research is needed on the orientation of CLT lamina arrangement according to the fiber arrangement of structural wood-based materials, and the block shear strength between lamina materials.

Rolling Shear Properties of Hybrid Cross-Laminated Timber

Cross-laminated timber (CLT) is an innovative wood product that can be used to build midrise and tall wood construction as an alternative to concrete, masonry, and steel. As floor, roof, and wall made of CLT is subjected to out-of-plane bending, rolling shear (RS) failure of cross-layers can arise prior to bending failure of the outermost layers, which governs the load-carrying capacity of CLT. In fact, the global deflections of CLT depend on the rolling shear modulus of cross-layers, which is much lower than shear modulus parallel to grain. Therefore, it is necessary to determine and improve the rolling shear strength and modulus of cross-layers. In this paper, several test methods were firstly summarized, after which the main influence factors on rolling shear properties were reviewed. Finally, seven configurations of hybrid CLT with three layers were tested to assess the rolling shear properties of hybrid CLT, in which the outer layers are made of Spruce-Pine-Fir (SPF) and the cross-layer is made of different materials such as birch, compressed wood (CW), laminated veneer lumber (LVL), Parallel strand lumber (PSL), plywood, oriented strand board (OSB), and glued laminated bamboo (GLB). The CLT made of SPF was also tested, whose rolling shear properties were regarded as reference. The rolling shear properties of GLB are about twice as high as those of SPF. Other materials do not exhibit superior rolling shear properties to SPF. The compressed wood shows a significant ductility in rolling shear failure.

Shear strength properties of hybrid (hinoki cypress and Japanese cedar) cross-laminated timber

In this study, the out-of-plane shear strength of hybrid cross-laminated timber (CLT) with outer layers of hinoki (hinoki cypress, Chamaecyparis obtusa) and inner layers of sugi (Japanese cedar, Cryptomeria japonica) is investigated for four different layer configurations. To investigate the influence from rolling shear properties of cross layers on the shear strength of CLT, stress analysis was conducted using the shear analogy method. The nominal shear strength, the maximum shear force divided by the cross-section of CLT, was in the 1.0–2.1 MPa range. Using the shear analogy method, the rolling shear modulus in the cross layer was determined as 72.9 MPa, which was comparable with the value obtained for laminae in previous study as well as the value confirmed by strain measurements in the present study. The magnitude of rolling shear stress in the cross layer was 0.9–1.1 times the average shear stress, which was negatively correlated with the nominal shear strength. From the regression line between the nominal shear strength and the magnitude of the shear stress in the cross layer, the mean shear strength of the cross layer was estimated to be 1.33 MPa.

Nonlinear Static Seismic Response of a Building Equipped with Hybrid Cross-Laminated Timber Floor Diaphragms and Concentric X-Braced Steel Frames

Simplified seismic design procedures mostly recommend the adoption of rigid floor diaphragms when forming a building’s lateral force-resisting structural system. While rigid behavior is compatible with many reinforced concrete or composite steel-concrete floor systems, the intrinsic stiffness properties of wood and ductile timber connections of timber floor slabs typically make reaching a such comparable in-plane response difficult. Codes or standards in North America widely cover wood-frame construction, with provisions given for both rigid and flexible floor diaphragms designs. Instead, research is ongoing for emerging cross-laminated-timber (CLT) and hybrid CLT-based technologies, with seismic design codification still currently limited. This paper deals with a steel-CLT-based hybrid structure built by assembling braced steel frames with CLT-steel composite floors. Preliminary investigation on the performance of a 3-story building under seismic loads is presented, with particular attention to the influence of in-plane timber diaphragms flexibility on the force distribution and lateral deformation at each story. The building complies with the Italian Building Code damage limit state and ultimate limit state design requirements by considering a moderate seismic hazard scenario. Nonlinear static analyses are performed adopting a finite-element model calibrated based on experimental data. The CLT-steel composite floor in-plane deformability shows mitigated effects on the load distribution into the bracing systems compared to the ideal rigid behavior. On the other hand, the lateral deformation always rises at least 17% and 21% on average, independently of the story and load distribution along the building’s height.

Prediction of withdrawal resistance for a screw in hybrid cross-laminated timber

The aim of this study was to predict the withdrawal resistance of a screw in hybrid cross-laminated timber (CLT) composed of two types of lamina layers. A theoretical model to predict the withdrawal resistance was developed from the shear mechanism between a screw and the layers in hybrid CLT. The parameters for the developed model were the withdrawal stiffness and strength that occurs when a screw is withdrawn, and the penetration depth of a screw in layers of a wood material. The prediction model was validated with an experimental test. Screws with two different diameters and lengths (Ø6.5 × 65 mm and Ø8.0 × 100 mm) were inserted in a panel composed of solid wood and plywood layers, and the withdrawal resistances of the screws were evaluated. At least 30 specimens for each group were tested to derive the lower 5th percentile values. As a result, the developed model predictions were 86–88% of the lower 5th percentile values of hybrid CLT from the properties of the lamina layer. This shows that the withdrawal resistance of hybrid CLT can be designed from the properties of its layer.