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This paper deals with the bonding characteristics of cross-laminated timber (CLT) panels made of Silver birch (Betula pendula Roth.), European aspen (Populus tremula L.), and Norway spruce (Picea abies (L.) H. Karst.) wood. Three-layered single-species CLT panels were manufactured using birch, aspen, and spruce lamellae bonded with a one-component polyurethane (PUR) adhesive. Spruce CLT panels were used as reference. The bonding characteristics of CLT were assessed based on bond shear strength, total and maximum delamination, and wood failure percentage. The reference spruce CLT met both criteria (Delamtot ≤ 10%, Delammax ≤ 40%) for passing the delamination test, where up to 80% of the test samples passed. The aspen and birch CLTs met the criterion for maximum delamination (26.5% and 33.2%, respectively), but exceeded the maximum allowed value for total delamination (12.7% and 13.2%, respectively). However, the minimum requirement of 70% wood failure percentage (WFP) was met for all CLT types, with aspen CLTs achieving 83.7% and birch CLTs 76.9%. The spruce CLTs achieved an average bond shear strength of 1.9 N/mm2, while both hardwood CLTs had significantly higher values, with the aspen CLT at 3.3 N/mm2 and the birch CLT at up to 3.9 N/mm2. Based on the results obtained, it can be concluded that cross-laminated timber (CLT) made from hardwoods like aspen and birch is suitable for environments with low humidity fluctuations. [ABSTRACT FROM AUTHOR]

A cross‐laminated timber rib panel is a floor system comprising cross‐laminated timber plates rigidly bonded to glued‐laminated timber 'rib' beams. A design method was developed to estimate the fire resistance of cross‐laminated timber rib panels, based on a bending load‐carrying model. The bending load‐carrying model calculates the bending load‐carrying capacity of cross‐laminated timber rib panels based on simulated temperature distributions of numerical models. The numerical models were validated against the experimental results of full‐scale fire resistance tests. The proposed design method is based on the overall approach of the current revised draft of EN 1995‐1‐2:2004, that is, prEN 1995‐1‐2:2023, and provides conservative estimates of the bending load‐carrying capacity. The effective width is one of the most important design parameters and its influence was studied in detail. A limit value of 60% of the effective width according to prEN 1995‐1‐1:2023 is proposed as effective width in fire. [ABSTRACT FROM AUTHOR]

The cross-laminated timber (CLT) shear-wall and glulam moment-resisting frame (CLTW–GMRF) dual system is a recently completed research prepared for the British Columbia (BC) Forestry Innovation Investment Ltd. With the introduction of new structural systems, the need to update existing building code becomes evident. Accordingly, this study evaluates the ductility-related force modification factor (Rd) of the CLTW–GMRF system for the National Building Code of Canada, utilizing the FEMA P-695 procedure. In two performance groups, 16 archetype buildings are designed considering different building storey heights, CLT shear-wall locations, and wall-frame moment proportions. Numerical model of the systems is developed in OpenSees and incremental dynamic analyses are conducted using 30 bi-directional ground motion records that represent the seismicity of Vancouver, BC, Canada. Collapse margin ratios are calculated to assess the adequacy of the trial Rd factors. The research determined that with an over-strength factor of 1.5, an Rd of 3 is found to be acceptable for the system. [ABSTRACT FROM AUTHOR]

Cross-Laminated Timber (CLT) and concrete composite structures represent an architectural system that integrates the strengths of both materials. In this innovative configuration, the CLT and concrete collaborate synergistically, harnessing their individual merits to achieve enhanced structural performance and functionality. Specifically, the CLT offers a lightweight design, superior bending resistance, and immense engineering plasticity, while concrete boasts exceptional compressive strength and durability. This study investigates the mechanical performance of CLT–concrete composite structures through quasi-static reciprocating loading tests in three full-scale CLT shear wall samples. Designed with varying initial prestressing forces and dimensions of the CLT panel, the prestressed CLT–concrete structures demonstrated a reduced dependence on the steel nodes, resulting in an increase in yield load, yield displacement, and maximum load-carrying capacity. Maximum capacity increased by 39.8% and 33.7% under initial prestressing forces of 23 kN and 46 kN on steel strands. Failure occurred due to localized compressive failure on prestressed steel strands and anchor plates. ABAQUS finite element analysis established three refined models, revealing that the increased initial prestressing force moderately enhanced stiffness but reduced ductility under similar cross-sectional dimensions. Furthermore, under consistent CLT material, dimensions, prestressing force, and loading conditions, prestressed CLT–concrete structures exhibited a higher maximum load-bearing capacity than prestressed CLT–steel composite structures. This study proposes structural design recommendations based on experimental and simulation results, incorporating specific assumptions. [ABSTRACT FROM AUTHOR]

Advancements in non-destructive evaluation systems for predicting mechanical properties of cross-laminated timber appear to have been limited to laboratory scale, reduced sample sizes, or difficult practical solutions for industry implementation. This study has developed classical vibration analysis methods for industry adoption in large-scale, rapid panel characterisation through frequency analysis. The non-destructive method allowed for the prediction of the elastic moduli in both axial directions (Ex and Ey) and shear moduli (Gxz, Gyz, and Gxy) for thin or thick plates. The comparison with the static reference method and non-destructive technique showed a good consistency for predicting the elastic and shear moduli of the cross-laminated timber with mean percentage differences for Ex, Ey, and Gxy of 5.2%, 7.9%, and 18.9%, respectively. An observation was made that the accurate determination of the mechanical properties required enough correctly identified frequencies/modes. Mode shapes generated from experimental data through modal assurance criterion were compared with finite element analysis to confirm the assessment method yielded frequencies specific to the panel, rather than other contributing effects (environment, boundary conditions, panel variability, mesh resolution). [ABSTRACT FROM AUTHOR]

As a sustainable construction material, timber is more promoted than steel, concrete, and aluminum nowadays. The building industry benefits from using timber based on several perspectives, including decarbonization, improved energy efficiency, and easier recycling and disposal processes. The cross-laminated timber (CLT) panel is one of the widely utilized engineered wood products in construction for floors, which is an ideal alternative option for replacing reinforced concrete. One single CLT panel has an outstanding flexural behavior. However, CLT cannot be extended independently without external connections, which are normally made of steel. This article proposes two innovative adhesive-free edge connections made of timber, the double surface (DS) and half-lapped (HL) connections. These connections were designed to connect two CLT panels along their weak direction. Parametric studies consisting of twenty models were conducted on the proposed edge connections to investigate the effects of different factors and the flexural behavior of CLT panels with these edge connections under a four-point bending test. Numerical simulations of all the models were done in the current study by using ABAQUS 2022. Furthermore, the employed material properties and other relevant inputs (VUSDFLD subroutines, time steps, meshes, etc.) of the numerical models were validated through existing experiments. The results demonstrated that the maximum and minimum load capacities among the studied models were 6.23 kN and 0.35 kN, respectively. The load–displacement responses, strain, stress, and defection distributions were collected and analyzed, as well as their failure modes. It was revealed that the CLT panels' load capacity was distinctly improved due to the increment of the connectors' number (55.05%) and horizontal length (80.81%), which also reinforced the stability. Based on the findings, it was indicated that adhesive-free timber connections could be used for CLT panels in buildings and replace traditional construction materials, having profound potential for improving buildings' sustainability and energy efficiency. [ABSTRACT FROM AUTHOR]

The perpendicular orientation of the cross-layer (s) makes Cross-laminated Timber (CLT) susceptible to reduced stiffness in out-of-plane bending. Orienting the cross layers at angles other than 90° could provide cost-effective layup customization for fabrication. This customization improvement has the potential to allow production of a panel with an optimized fiber content from regional resources for a requested structural performance and span. Under out-of-plane bending, shear deformation occurs in the cross layers along the radial-tangential plane. This reduced stiffness in CLT panels can be improved by varying the grain orientation of the cross-layers away from perpendicular-to-grain (90°), and closer to parallel-to-grain (0°). This paper studies the shear stiffness of a pair of asymmetric angle-ply layers rotated at angles from 90 to 70, 40, 20, 10, and 0°. These two layers with varying grain orientations were assumed to be representative of the inner layers of a four-ply Diagonal Cross-laminated Timber panel. For this purpose, a theoretical model based on Hankinson's formula was developed, and compared to empirical testing from two-plate shear tests. These predicted and observed behaviors were then compared to numerical modeling using the Finite Element Method. The results of the three methods showed an agreement in predicting an increase in shear stiffness when the angle-ply orientation of the layers decreases from 90 to 0°. The results indicated that Hankinson's formula seems to be a conservative theoretical predictor for the shear stiffness of diagonal layers. Regarding the experimental results, orienting the cross layers to an angle between 70 and 40° was shown to improve the shear stiffness by 10 and 46% respectively. This research provides insights into innovations towards CLT development with improved shear stiffness using diagonally-oriented layers. [ABSTRACT FROM AUTHOR]

In this study, the finite element method (FEM) was used to determine the effect of the optimal angle of the thread and double thread application among self-tapping screw (STS) design information on the improvement of the withdrawal capacity of the connection. It was modeled by reflecting the design information of an Italian STS distributed in the domestic wooden building market, and the stress distribution of the connections was compared according to the change in the thread angle. A cross laminated timber (CLT) composed of five layers was modeled as a member. The STS modeling was centered on the threaded area, and two threaded angles were applied: 90° and 95°. Additionally, the stress changes were compared when double threads located in the middle of the thread pitch in the screw pitch were applied to improve the withdrawal capacity of the connection. The domestic STSs were manufactured using four materials and two shapes. The finite element analysis and strength performance tests of the STS types indicated that the material properties, angle of the screw thread, and shape of the screw thread affect the Korean CLT withdrawal capacity.

The effect of densification of the laminas was studied relative to the shear performance of cross-laminated timber (CLT) specimens submitted to the bending test. The three-layered CLT panels were fabricated using loblolly pine (Pinus taeda L.). A compression ratio (CR) of 50% was used to densify the lumber using the thermomechanical densification technique. The process included plasticizing the lumbers by soaking them in boiling water for 10 minutes and then hot-pressing to the target thickness at 140 °C. Four groups were made, i.e., a control sample with all three layers non-densified, only mid-layer densified, all layers densified, and all layers planed to the same thickness of densified layers. Specimens were tested in short-span bending with a span-to-depth ratio of eight. For specimens having densified mid-layer, the failure mode changed from rolling shear to tensile failure of the outer layer, and the maximum shear stress was increased by 34%. Densification of the mid-layer at CR of 16% was sufficient to change the failure mode from rolling shear in mid-layer to tensile in outer layer. In the case of all-layer-densified specimens, the maximum rolling shear strength was increased by 129% compared to the control.

Cross-Laminated Timber (CLT) panels have many structural benefits but do not have much thermal resistance. We have developed a solution to insulate CLT structures that uses high-performance insulation panels that provide R-values up to R40/inch. The CLT panels are made of layers of wood laminates (three, five, seven or more). The solution replaces some of the wood laminates in the CLT production with the insulation panels in a staggered fashion so that the wood laminates maintain contact throughout the panel, ensuring the CLT panel's structural integrity. The insulated CLT panels have factory-installed water-resistive barriers reducing the installation time by eliminating installing insulation and water-resistive barriers on site. Per simulations, the CLT/insulation panel achieved code-required insulation levels with commonly available insulation materials. The significance of the thermal mass of CLT/insulation hybrid building envelopes was quantified by comparing the whole building energy performance and peak demand of traditional low mass and CLT wall assemblies resulting in up to 7% reduction in peak demand for cooling in Knoxville, TN, in a multifamily building. Buildings contribute over 40 percent of carbon emissions. The proposed CLT/insulation hybrid building envelope addresses both operational and embodied carbon by having high thermal resistances due to the embedded insulation sections and eliminating the use of high embodied carbon materials such as steel and concrete. The carbon benefit is estimated. [ABSTRACT FROM AUTHOR]

In this study, the vibration serviceability of multi-storey timber buildings is addressed. The core of this study pertains to the preparation of a comprehensive finite element model to predict modal properties for an accurate vibration serviceability checking. To that end, findings obtained from studying three multi-storey timber buildings are summarized and discussed. Two of the buildings (of seven and eight storeys) consist entirely of cross-laminated timber (CLT), while the third is a five-storey hybrid CLT-concrete building. Thanks to the detailed finite element models and modal testing results, one has the capability to conduct sensitivity analyses, classical and Bayesian model updating, and uncertainty quantifications. With these methodologies, influential modelling parameters as well as the sources of modelling error were identified. This allowed for conclusions to be drawn about the in-plane shear stiffness of the constructed walls (whose higher value causes the natural frequencies to increase by up to 25%), the soil deformability (which may cause the natural frequencies to drop by up to 20%), and the perpendicular-to-the-grain deformation of floor slabs (which may lead to an overestimation of a fundamental frequency by up to 8%). [ABSTRACT FROM AUTHOR]

This study investigates the load-bearing properties of cross-laminated timber (CLT) under compression perpendicular to the grain. Different series of CLT panels with varying layups, layer thicknesses, and overall depths were tested. Also, the compression perpendicular to the grain properties of CLT plate specimens is compared against clear wood and cubic CLT specimens. The results show a 30% reduction in modulus perpendicular to the grain for cubic samples compared to clear specimens. Increasing the number of layers from three to five leads to a 21% higher modulus, while increasing the overall depth from 105 to 175 mm results (with the same number of layers) in a 17% reduction. The overall depth significantly affects the CLT's modulus and strength under compression perpendicular to the grain. The study also compares two analytical models for determining the transversal compression factor, kc,90. Although the models showed satisfactory results for thinner CLTs, their accuracy decreased with greater panel depth. These findings enhance the understanding of CLT panels for structural applications. [ABSTRACT FROM AUTHOR]

This study was part of a larger project investigating the feasibility of using ponderosa pine (Pinus ponderosa, PP) harvested from forest restoration programs in the Northwestern United States for low-rise modular buildings. The panels have a standard width of 1.2 m to consider dimensions available from local manufacturers. To use these panels as walls or floors, they must be joined using in-plane connections. The stiffness and capacity of these connection systems under reversal lateral loading affect the behavior of the multipanel wall systems. Such multipanel systems are proposed for use in modular construction, with the goal of finding suitable market outlets for PP cross-laminated timber (CLT). In-plane connections within the multipanel system here play the role of the intramodular connection, while intermodular connections connect different multipanel systems to form a structure. Butt joints with 45° screws and a bolted point-type connection system were selected as intramodular and intermodular connections, respectively, due to their suitability for prefabrication and ease of installation. The aim of the study was to determine the mechanical characteristics of these two types of connections in PP CLT. Ten intramodular connections under monotonic and cyclic loading in shear and tension, and 12 intermodular connections in monotonic and cyclic in two different configurations were tested. The resulting force-displacement curves were used to extract the mechanical characteristics of the connections, which were then compared to the performance of the same type of connections in CLT panels made from other wood species. The intramodular connection showed high ductility in shear and low to medium ductility in tension, while the intermodular connection had lower initial stiffness compared to tests of commercial CLT in all tested directions except compression. [ABSTRACT FROM AUTHOR]

The use of timber as a building material is becoming increasingly popular thanks to its superior environmental performance compared with concrete and steel. However, timber structures rely on solid connections to improve their weak expansibility. Steel connections can be prone to corrosion over time, leading to the decreased structural integrity. Additionally, steel connections require more material and energy to manufacture and install compared with timber connections. This article focuses on the flexural performance of cross-laminated timber (CLT) panels with adhesive-free edge connections under four-point bending tests. First, numerical models of experimentally tested CLT panels were constructed using the finite element (FE) software ABAQUS. Then, these FE models were validated with the comparisons of their results with those of the experimental tests. Afterward, four new adhesive-free edge connections using timber for the CLT panels were developed in this study, helping sustainable construction. Utilizing the designed edge connections of the current study, forty-one parametric studies were numerically conducted on the connected CLT panels to investigate their ultimate loads, strains, displacements, moment capacities, failure modes, and effective stiffness. The factors affecting the edge connections’ load-bearing capacity were also examined and discussed. The study provides helpful insights into the development of CLT as a sustainable construction material with improved adhesive-free edge connections.

This study aims to contribute to limited research evidence for evaluating air leakage through Canadian manufactured CLT, by initiating research to characterize and quantify air leakage paths across CLT panels and evaluate the impact of additional air barrier system components on CLT. Understanding air leakage across CLT is important to the continuous development of design and construction practices towards ensuring the performance of CLT buildings. Through experimental testing of various panel parameters, metrics including the air leakage rate, normalized equivalent leakage area, as well as the flow exponent and flow coefficient were measured. For 3-ply and 5-ply CLT panels utilized in this research, significant air leakage through panel edges compared to air leakage through the panel face was observed due to unglued edge joint gaps typical to Canadian manufactured CLT. Further, sealing panel edges with an effective air barrier material such as a self-adhered membrane to reduce air leakage from 4 to 12 L/sm2 to 0.09–1.4 L/sm2 was not enough to meet more stringent thresholds for air barrier assemblies at 0.1 L/sm2 at a 75 Pa pressure differential.

Abstract Most of the currently employed methods, such as Gamma method and shear analogy method, to estimate the bending stiffness and bending capacity of cross-laminated timber (CLT) beams, are computationally extensive. In our previous study, a rolling shear analysis (RSA)-based method, which simplifies the calculation, was developed to determine the shearing capacity of CLT beams. In the present study, the authors expand upon the RSA method to determine the apparent stiffness and bending capacity of 3- and 5-layer CLT beams. By considering the shear deformation of cross layers, simplified formulas to determine the apparent bending stiffness of CLT beam was derived. Two schemes to determine the CLT bending capacity were proposed. One is based on the shear stress analysis, and the other is based on the formula specified in Canadian standard, CSA O86, by replacing the effective stiffness with the apparent stiffness. Test results from the authors and the other researchers were adopted to validate the method. The findings showed that the RSA method, using the apparent stiffness obtained from the proposed method along with the bending capacity formula in CSA O86, can provide a simpler and more reliable estimation of the apparent bending stiffness and bending capacity of CLT beams as compared to the Gamma method and shear analogy method.

This paper deals with the bonding characteristics of cross-laminated timber (CLT) panels made of Silver birch (Betula pendula Roth.), European aspen (Populus tremula L.), and Norway spruce (Picea abies (L.) H. Karst.) wood. Three-layered single-species CLT panels were manufactured using birch, aspen, and spruce lamellae bonded with a one-component polyurethane (PUR) adhesive. Spruce CLT panels were used as reference. The bonding characteristics of CLT were assessed based on bond shear strength, total and maximum delamination, and wood failure percentage. The reference spruce CLT met both criteria (Delamtot ≤ 10%, Delammax ≤ 40%) for passing the delamination test, where up to 80% of the test samples passed. The aspen and birch CLTs met the criterion for maximum delamination (26.5% and 33.2%, respectively), but exceeded the maximum allowed value for total delamination (12.7% and 13.2%, respectively). However, the minimum requirement of 70% wood failure percentage (WFP) was met for all CLT types, with aspen CLTs achieving 83.7% and birch CLTs 76.9%. The spruce CLTs achieved an average bond shear strength of 1.9 N/mm2, while both hardwood CLTs had significantly higher values, with the aspen CLT at 3.3 N/mm2 and the birch CLT at up to 3.9 N/mm2. Based on the results obtained, it can be concluded that cross-laminated timber (CLT) made from hardwoods like aspen and birch is suitable for environments with low humidity fluctuations.

Most of the currently employed methods, such as Gamma method and shear analogy method, to estimate the bending stiffness and bending capacity of cross-laminated timber (CLT) beams, are computationally extensive. In our previous study, a rolling shear analysis (RSA)-based method, which simplifies the calculation, was developed to determine the shearing capacity of CLT beams. In the present study, the authors expand upon the RSA method to determine the apparent stiffness and bending capacity of 3- and 5-layer CLT beams. By considering the shear deformation of cross layers, simplified formulas to determine the apparent bending stiffness of CLT beam was derived. Two schemes to determine the CLT bending capacity were proposed. One is based on the shear stress analysis, and the other is based on the formula specified in Canadian standard, CSA O86, by replacing the effective stiffness with the apparent stiffness. Test results from the authors and the other researchers were adopted to validate the method. The findings showed that the RSA method, using the apparent stiffness obtained from the proposed method along with the bending capacity formula in CSA O86, can provide a simpler and more reliable estimation of the apparent bending stiffness and bending capacity of CLT beams as compared to the Gamma method and shear analogy method. [ABSTRACT FROM AUTHOR]

The end-grain bonding of timber components using the Timber Structures 3.0 technology (TS3) is an advancing construction method in timber engineering. This technology allows the realisation of any plate size by bonding plates on-site where low temperatures influence the performance. Therefore, investigations are underway to evaluate the influence of the low temperatures on the curing process. Additionally, research is in progress to discover techniques to reduce any adverse effects of low curing temperatures on the mechanical properties of the bond. The implementation of particular measures, such as the inclusion of milled heating wires into the joint and the pre-heating of the joint with a hot air blower, has been identified as advancing the potential for grouting even in the face of low external temperatures, as recent research has indicated. [ABSTRACT FROM AUTHOR]

A strengthening of cross-laminated timber (CLT) by a composite effect with steel girders can widen the application of CLT ceilings to spans over 8 m. Most possible shear connectors are not stiff enough to ensure a completely rigid composite. At present, it has not been sufficiently clarified how the elastic bending behaviour is affected by the influences of the flexibility of continuously and discontinuously shear connectors, the number of transverse layers of the CLT and the span width. Thus, 4-point bending tests and vibration tests were performed with different cross-section configurations and two different shear connectors in continuous and discontinuous spacing in spans of 8.10 and 10.80 m. To date, no comparable bending tests have been carried out in these spans, with more than five CLT-layers and discontinuously arranged shear connectors. The composite beams deformed linear-elastically until the yield strength of the steel was reached. The composite effect increased the elastic bending stiffness up to twofold compared to no composite. Increasing the span resulted in a higher bending stiffnesses. The elastic bending stiffness of the composite beams with shear studs was significantly lower than with fully threaded screws. For a worthwhile composite effect, both materials should contribute a balanced share of the stiffness. A larger share of the CLT in the bending stiffness compared to the steel girder created a higher elastic limit load capacity but an equivalent bending stiffness. It is necessary to discuss which cross-sectional configurations are appropriate in terms of load bearing capacity, economic efficiency and sustainability. To assess the practical application potential in spans between 8 and 12 m, the tests were additionally evaluated for the equivalent load level for the serviceability limit state of office or industrial buildings. For spans of 8.10 m, the limits according to EC5 for the initial deflection of L/300 and fundamental frequency of 8 Hz can be met. For spans of 10.80 m, only less strict deflection limits are achieved. However, by increasing the degree of composite through more shear connectors, compliance with the limit values mentioned could already be possible with the crosssections tested. In case of fire, it may be sufficient to consider only the CLT with the reduced cross-section method (EN 1995-1-2) for load transfer, even for longer fire durations. [ABSTRACT FROM AUTHOR]

Mass-timber construction is becoming more prevalent in Australia and around the world. However, as these mass-timber buildings become taller, it is important to consider robust detailing against accidental damages to major load-bearing elements and thereby avoid potential progressive collapse scenarios. In order to better understand the robustness of typical mass-timber buildings, this study analyzed a typical 10-story midrise mass-timber building subjected to different progressive collapse scenarios. A scenario-independent approach was considered in the analysis, which includes the sudden removal of a load-bearing glulam column from the midrise mass-timber building. It was observed that when internal ties and bracings were provided, the robustness of the building was not affected as there was an alternative load path created. The orthogonal tie beam and diagonal bracing can transfer about 60% and 20% of the axial loads of the removed column to the adjacent columns, respectively. It was found that the building becomes vulnerable when no internal tie or bracing is available to transfer the accidental load. In this scenario, higher stiffness of the cross-laminated timber panel-to-panel joint can be adopted to improve the robustness of mass-timber building. [ABSTRACT FROM AUTHOR]

This paper introduces a method to create a moment-resisting edge connection between two cross-laminated timber (CLT) panels. With this connection, two-way spanning cross-laminated timber slabs can be realised, where the span exceeds the manufacturing and transport-related width of the individual CLT panels. Until now, mostly on-site gluing solutions have been suggested for such connections. In this study, a solution using a timber–concrete–composite (TCC) system is proposed. For this, self-tapping screws are inserted along the edge face of the CLT component, enabling the formation of a lap splice between two adjacent CLT elements. This lap splice is reinforced by additional rebars and filled with concrete. This means that only familiar, easy-to-handle materials are used on-site, and there is no need for adhesives, which can be difficult to apply. To evaluate the load-bearing capacity of the connection, it was subjected to a pure bending load in four-point bending tests, where load-bearing capacities of up to 70% of the characteristic load-bearing capacity of the solid CLT elements were achieved. An analytical approach for a simplified engineering calculation model is introduced to determine the load acting upon the screws. Based on the experimental results, it is shown that the analytical approach is able to adequately represent the load-bearing capacity of the connection. The analytically determined forces on the screws may then be used to carry out further verifications on this connection method. [ABSTRACT FROM AUTHOR]

High-rise wooden buildings are increasing in popularity, and they typically include cross-laminated timber in the structure. Taller buildings result in higher loads on the junctions lower down in the building, which are suggested in the literature to negatively affect the sound insulation. This study involved measurement of the vibration reduction index in four different CLT buildings, varying in height and junction details. A total of 12 junctions were measured at both high and low levels in the buildings. Among these, 10 junctions had resilient interlayers with different stiffnesses dependent on the designed quasi-permanent load, while 2 junctions lacked resilient interlayers. The results indicated that the vibration reduction index decreases lower down in the building mainly for the Wall–Wall path. The findings were consistent for all measured junctions above 400 Hz for the Wall–Wall path and for the majority of the measurements of the remaining frequency range, 400 Hz and below. The observed difference in the vibration reduction index could significantly impact the final result if a high-rise building has several flanking paths that affect the sound insulation between two apartments, and this needs to be considered during the design phase. Similar effects were shown for buildings both with and without resilient interlayers in the junctions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Embedment strength is an important factor in the design and performance of connections in timber structures. This study assesses the embedment strength of lag screws in three-ply cross-laminated timber (CLT) composed of densified poplar wood with densification ratios of 25% and 50%, under both longitudinal (L) and transverse (T) loading conditions. The embedment strength was thereafter compared with that of CLT reinforced with glass-fiber-reinforced polymer (GFRP). The experimental data was compared with results obtained using different models for calculating embedment strength. The findings indicated that the embedment strength of CLT specimens made of densified wood and GFRP was significantly greater than that of control specimens. CLT samples loaded in the L direction showed higher embedment strength compared to those in the T direction. In addition, 50% densification had the best performance, followed by 25% densification and GFRP reinforcement. Modelling using the NDS formula yielded the highest accuracy (mean absolute percentage error = 10.31%), followed by the Ubel and Blub (MAPE = 21%), Kennedy (MAPE = 28.86%), CSA (MAPE = 32.68%), and Dong (MAPE = 40.07%) equations. Overall, densification can be considered as an alternative to GFRP reinforcement in order to increase the embedment strength in CLT. [ABSTRACT FROM AUTHOR]

Floor diaphragms are structural elements mainly responsible for transmitting lateral loads to the adjoining vertical members of the Seismic-Force-Resisting System (SFRS). Under significant seismic events, the actual in-plane stiffness of floor diaphragms affects patterns of load distribution in-between horizontal and vertical elements and, as such, contributes to the local nonlinear response and the global dynamic behavior. However, in SFRS with mass timber and hybrid timber-based floor diaphragms, neither design provisions nor procedures exist to account for its in-plane flexibility. To highlight the influence of the actual in-plane stiffness of diaphragms on a timber-steel hybrid building system, this paper analyzes its dynamic response via nonlinear dynamic analysis. The OpenSees framework is adopted to develop three finite-element building models that feature diaphragms with (i) rigid behavior, (ii) actual members and connections diaphragm subassembly behavior, including panel-to-panel slab connections, or (iii) neglecting the contribution of the slab connections, respectively. The SFRS of the building entails a Special Concentrically Braced Frame whose nonlinear behaviors are explicitly simulated, including global buckling, tensile yielding, and post-buckling behaviors. The collapse fragility analysis reveals that the conditional probability of exceeding all three considered limit states given any level of ground motion intensity for the SFRS equipped with the CLT-steel floor diaphragm is close to that of the SFRS with rigid diaphragm behavior. Removal of CLT panel-to-panel connections attracts disproportionate and excessive lateral deformation demands towards the unbraced frames due to the increased in-plane diaphragm flexibility. [ABSTRACT FROM AUTHOR]

Japan is actively promoting the application of cross-laminated timber (CLT) in construction to utilize plantation forests efficiently and fulfil its climate commitments. Although CLT has unique structural properties and environmental advantages, understanding the environmental burden of CLT manufacturing remains scarce. This study uses input–output analysis to evaluate the greenhouse gas (GHG) emissions from CLT manufacturing. An extended input–output table was created to measure the GHG emissions by investigating the revenue and expenditure data of the largest CLT manufacturers in Japan in 2020, combined with the energy and emission intensity data. The results showed that electricity, activities not elsewhere classified, road freight transportation (except self-transportation), timber, and logs were the main sectors contributing to GHG emissions from CLT manufacturing. In addition, the environmental burdens of the cement and steel sectors were evaluated for comparison with the same increase in the final demand. We found that CLT manufacturing emits significantly fewer GHGs than the cement and steel sectors. These findings highlight the potential of CLT in reducing environmental burden, particularly in construction and civil engineering, emphasizing the importance of renewable energy use and efficient raw material transportation. [ABSTRACT FROM AUTHOR]

The mechanical properties of materials such as lumber (L), glued laminated timber (GLT), cross-laminated timber (CLT), and Ply-lam CLT (P), which are laminated in cross layers, were compared. As a result, the modulus of elasticity (MOE) was 9.7 to 10.3 GPa, showing no significant difference between the materials. Modulus of rupture (MOR) of L and GLT showed higher strength than that of CLT and P. MOR of CLT and P was at the same level, and there was no difference in strength according to the plywood and lumber arranged alternately. Alternatively, there was a difference in the coefficient of variation of the materials, and CLT and P was 20.2% and 11.8%, respectively; therefore, uniform properties can be secured when using plywood. The compression strength showed the highest compression strength in the order of GLT, L, P, and CLT. P was failure by buckling+delamination, but other materials showed failure by only buckling. The adhesion of P passed the glulam standard (7.0 MPa), and the delamination ratio was very low at 0.41%. It can be used together with CLT. This study is expected to be used as basic data for establishing quality standards.

Cross-Laminated Timber (CLT) and concrete composite structures represent an architectural system that integrates the strengths of both materials. In this innovative configuration, the CLT and concrete collaborate synergistically, harnessing their individual merits to achieve enhanced structural performance and functionality. Specifically, the CLT offers a lightweight design, superior bending resistance, and immense engineering plasticity, while concrete boasts exceptional compressive strength and durability. This study investigates the mechanical performance of CLT–concrete composite structures through quasi-static reciprocating loading tests in three full-scale CLT shear wall samples. Designed with varying initial prestressing forces and dimensions of the CLT panel, the prestressed CLT–concrete structures demonstrated a reduced dependence on the steel nodes, resulting in an increase in yield load, yield displacement, and maximum load-carrying capacity. Maximum capacity increased by 39.8% and 33.7% under initial prestressing forces of 23 kN and 46 kN on steel strands. Failure occurred due to localized compressive failure on prestressed steel strands and anchor plates. ABAQUS finite element analysis established three refined models, revealing that the increased initial prestressing force moderately enhanced stiffness but reduced ductility under similar cross-sectional dimensions. Furthermore, under consistent CLT material, dimensions, prestressing force, and loading conditions, prestressed CLT–concrete structures exhibited a higher maximum load-bearing capacity than prestressed CLT–steel composite structures. This study proposes structural design recommendations based on experimental and simulation results, incorporating specific assumptions.

As a sustainable construction material, timber is more promoted than steel, concrete, and aluminum nowadays. The building industry benefits from using timber based on several perspectives, including decarbonization, improved energy efficiency, and easier recycling and disposal processes. The cross-laminated timber (CLT) panel is one of the widely utilized engineered wood products in construction for floors, which is an ideal alternative option for replacing reinforced concrete. One single CLT panel has an outstanding flexural behavior. However, CLT cannot be extended independently without external connections, which are normally made of steel. This article proposes two innovative adhesive-free edge connections made of timber, the double surface (DS) and half-lapped (HL) connections. These connections were designed to connect two CLT panels along their weak direction. Parametric studies consisting of twenty models were conducted on the proposed edge connections to investigate the effects of different factors and the flexural behavior of CLT panels with these edge connections under a four-point bending test. Numerical simulations of all the models were done in the current study by using ABAQUS 2022. Furthermore, the employed material properties and other relevant inputs (VUSDFLD subroutines, time steps, meshes, etc.) of the numerical models were validated through existing experiments. The results demonstrated that the maximum and minimum load capacities among the studied models were 6.23 kN and 0.35 kN, respectively. The load–displacement responses, strain, stress, and defection distributions were collected and analyzed, as well as their failure modes. It was revealed that the CLT panels’ load capacity was distinctly improved due to the increment of the connectors’ number (55.05%) and horizontal length (80.81%), which also reinforced the stability. Based on the findings, it was indicated that adhesive-free timber connections could be used for CLT panels in buildings and replace traditional construction materials, having profound potential for improving buildings’ sustainability and energy efficiency.

Background and verification principles for the fire protection design of cross‐laminated timber constructions – part 2 The two‐part paper describes the current state of the art about fire design methods for cross‐laminated timber elements and structures and describe differences in comparison to the design with solid timber. The second part of the paper explains the approaches for the separating function of protected and unprotected cross laminated‐timber elements, give design guidance about fire safe detailing and about the influence of visible timber members and elements regarding to the fire dynamic. [ABSTRACT FROM AUTHOR]

Cross-laminated timber (CLT) is increasingly being utilized in Europe, North America and elsewhere due to its superior mechanical properties and environmental-friendly performance. Considering regions and countries, such as China, those are scarce in structural wood resource but rich in bamboo forest, an idea of introducing bamboo into CLT system has been proposed to form a novel composite material, named as cross-laminated bamboo and timber (CLBT). This paper focuses on the comparison of thermal insulation performance of CLBT and CLT panels. The thermal resistance and transmittance of CLT and CLBT wall specimens were measured by the Guarded Hot Box test. A calculation method provided by ISO standard and a finite element (FE) model were also used to evaluate the thermal resistance of CLT and CLBT panels. Based on the proposed FE model, some parametric analysis was performed through 11 CLBT panels with different compositions, including the layer number of glubam and timber, the thickness of extruded polystyrene and the use of gypsum board and screws. Moreover, the feasibilities of these CLBT panels were evaluated for the application in different climate regions of China and the United States in accordance with the corresponding Chinese and American building energy efficiency standards, respectively. It can be finally concluded that, the development and application of CLBT contributes to achieving the low carbon sustainable features of structures, which is due to the good carbon sequestration ability of its component materials (i.e., timber and bamboo) as well as the good insulation performance of CLBT panels. [ABSTRACT FROM AUTHOR]

Cross-Laminated Timber (CLT) is a quasi-rigid composite engineered timber product that can assist the building industry in reducing embodied carbon emissions. The adoption of CLT in architectural design is of great importance to help to achieve China's dual carbon goals. This study aims to understand the factors and their effects on influencing architects' intentions to adopt this low-carbon building technology. It applied the theory of diffusion of innovation (DOI), incorporated architects' innovativeness and material properties of cross-laminated timber and used partial least squares structural equation modelling (PLS-SEM) to construct an adoption model. The adoption of CLT was found to depend on architects' novelty seeking and independent judgement making as well as the trialability, observability, relative advantage and riskiness. Observability had the most significant impact on the intention to use cross-laminated timber, followed by trialability, riskiness and relative advantage. It is imperative to increase the extent to which CLT can be observed and experienced by design professionals, to increase the publicity of its benefits, and to address barriers to uptake. Significant differences were found between architects with different years of work experience, which will help to develop tailored strategies for better promoting cross-laminated timber in China. [ABSTRACT FROM AUTHOR]

Most previous research on seismic performance of cross-laminated timber (CLT) structures focused on platform-type construction. This paper investigates the seismic performance and collapse risk of a balloon-framed CLT school building, designed for Vancouver, Canada. Incremental dynamic analysis was performed using a three-dimensional numerical model. Experimental data from connection- and wall-level tests were used to calibrate and validate the model. Twenty-one ground motions (crustal, subduction inslab, and interface) were selected. The results showed the building well met the 2% design drift limit. It had 4.2% probability of collapse at design level by considering uncertainties with a collapse margin ratio of 3.18. [ABSTRACT FROM AUTHOR]

Structural tests for seven full-scale cross-laminated timber (CLT) shear walls were conducted under cyclic lateral loading to investigate the feasibility of using fast-growing poplar in CLT structures. Connection tests with monotonic loads were performed to calculate the later bearing capacity of CLT shear walls. The effects of wood species, artificial accelerated aging, vertical step joint, and laminate strength class on the later performance of CLT were determined. Test results show that poplar CLT panels had potential application in CLT structures, with only an 8% difference in structural properties compared to spruce CLT. Accelerated aging reduced the mechanical properties of poplar CLT and converted its failure mode from plasticity to brittleness. The elastic stiffness of a poplar CLT shear wall with a vertical step joint decreased, but the energy dissipation capacity increased 3.3-fold. The lamina strength class was not positively related with the lateral bearing capacity of these walls. [ABSTRACT FROM AUTHOR]

In order to obtain the comprehensive compressive properties of cross-laminated timber (CLT), compressive strength tests were conducted on the CLT specimens made of spruce-pine-fir (SPF). The compressive strength, Poisson's ratio, and elastic modulus of CLT were calculated based on composite laminate plate theory, aiming to provide a reference for the mechanical properties testing of CLT. Nine CLT specimens with same dimensions were tested under axial compression to investigate the variation patterns of the ultimate bearing capacity, longitudinal strain, transverse strain, and Poisson's ratio. The theoretical bearing capacity of specimens was predicted according to the Chinese Standard for design of timber structures and verified with finite element modelling. The load-axial displacement curve showed a typical bifurcation characteristic, indicating that the specimens under axial pressure experienced elastic and elasto-plastic stages to failure, and the equivalent elastic modulus of SPF obtained by conversion was 10 011.57 MPa. The compressive strength and the Poisson's ratio were obtained as 35.16 MPa and 0.39, respectively. The theoretical calculated values generally fit the test results well. The simulated results in elastic stage were in good agreement with the test values. [ABSTRACT FROM AUTHOR]

Cross-Laminated Timber (CLT) panels have many structural benefits but do not have much thermal resistance. We have developed a solution to insulate CLT structures that uses high-performance insulation panels that provide R-values up to R40/inch. The CLT panels are made of layers of wood laminates (three, five, seven or more). The solution replaces some of the wood laminates in the CLT production with the insulation panels in a staggered fashion so that the wood laminates maintain contact throughout the panel, ensuring the CLT panel’s structural integrity. The insulated CLT panels have factory-installed water-resistive barriers reducing the installation time by eliminating installing insulation and water-resistive barriers on site. Per simulations, the CLT/insulation panel achieved code-required insulation levels with commonly available insulation materials. The significance of the thermal mass of CLT/insulation hybrid building envelopes was quantified by comparing the whole building energy performance and peak demand of traditional low mass and CLT wall assemblies resulting in up to 7% reduction in peak demand for cooling in Knoxville, TN, in a multifamily building. Buildings contribute over 40 percent of carbon emissions. The proposed CLT/insulation hybrid building envelope addresses both operational and embodied carbon by having high thermal resistances due to the embedded insulation sections and eliminating the use of high embodied carbon materials such as steel and concrete. The carbon benefit is estimated.