Timber Panels Research Articles

Feasibility of a Local Production Chain for Structural Timber in Sardinia, Italy

The construction sector is currently responsible for over 30% of the consumption of natural resources and the release of solid waste and pollution into the environment. This situation is even more serious in closed communities such as islands, economically highly dependent on the outside world. One of the possible interventions to reverse this trend is the use of eco-sustainable construction materials such as wood, produced through supply chains with a low environmental impact. This paper reports on a research activity that analyzed the feasibility of implementing a sustainable local supply chain in Sardinia to produce Cross-Laminated Timber (CLT) panels made of locally grown wood. This research has experimentally carried out the entire supply chain process: (i) choice and collection of the raw material in the forest for producing strength-graded boards to manufacture laminated timber, (ii) manufacturing of CLT panel prototypes, and (iii) determination of CLT panels’ mechanical performance through laboratory tests. This experimentation allowed, on the one hand, to evaluate the performance and competitiveness of CLT panels made of local wood, and on the other hand, to identify the criticalities that currently hinder the implementation of this supply chain in Sardinia, and to propose possible actions to solve them.

Numerical investigation of lateral behaviour of steel‐timber hybrid frames

AbstractThis paper examines the response of steel‐timber hybrid (STH) lateral stability systems for medium‐rise buildings. A ten‐storey baseline STH structure was designed to codified procedures and compared with a steel‐concrete composite structure. Detailed numerical models were constructed in which specific constitutive representations were assigned to steel‐timber and timber‐timber connections. Parametric investigations on the STH structure were carried out in which the cross laminated timber panel layups, timber shear wall length, and connection characteristics were modified. The study indicated that the STH structure had larger lateral deformations compared to the steel‐concrete structure, both within code limits. For the same design loads, the reduction in self‐weight from the steel‐concrete structure to the STH structure was 73.1%, whilst the floor depth was reduced by 17.2%, respectively. Parametric studies showed that the lateral response of STHs is generally improved with the effective thickness of the timber infill panel and is influenced by the panel layup. Increasing the shear wall length generally enhances the lateral stiffness, yet the overall performance is reduced with the increase of panel connections. The reduction in self‐weight, member sizes and replacement of the concrete with timber led to a reduction in embodied carbon of more than 32.7% whilst achieving similar structural performance.

Wood Diaphragm Deflections. I: Generalizing Standard Equations Using Mechanics-Based Derivations for Panel Construction

Horizontal wood diaphragm systems, whether decked with conventional or mass timber panels, transfer wind and seismic loads to vertical elements of a lateral force-resisting system (LFRS), in flexible, rigid, or semirigid fashion. Characterizing and calculating the resulting diaphragm deflections determines the distribution of forces to critically loaded components and a significant portion of lateral building translations and rotations. Deflection equations for sheathed wood structural panel (WSP) diaphragms are well established in US design standards in a four-term expression that models flexural, shear, and fastener-slip deformations, and its full derivation using principles of mechanics is provided herein. Derivations of similar equations for cross-laminated timber (CLT) diaphragms have yet to unfold, despite growing industry consensus that CLT panels make efficient slabs and decks. In this first of two companion papers, the corrected full derivation of the current four-term WSP diaphragm deflection expression is provided and assessed, and two ways to quantify the cumulative contribution of fastener slip are presented to expand its usage to a wider variety of WSP and CLT configurations in current use. Building on this generalized mechanics-based derivation, the authors are able to propose and assess in the companion paper a unified diaphragm deflection model to compute both WSP and CLT diaphragm deflections as implemented under current practice and guide further development.

Full-scale testing of masonry-infilled RC frames retrofitted with cross-laminated timber panels

This paper presents the results from an experimental study on an innovative timber-based seismic retrofit solution for existing reinforced concrete (RC) buildings. The intervention aims at enhancing the overall seismic resistance of RC framed structures with a light, cost-effective, sustainable, and reversible approach, allowing possible integration with energy efficiency upgrades. The retrofit technique relies on cross-laminated timber (CLT) panels mechanically connected through steel fasteners to the RC frame. This strengthening technique is investigated experimentally for the first time in this paper. The study examines two intervention configurations with different degrees of invasiveness: the first (RC-TP) involves replacing the existing masonry infill wall with a CLT panel, whereas the latter (RC-TPext) consists in applying the panel to the outer face of the frame. Both retrofit configurations were assessed experimentally through cyclic quasi-static in-plane tests on full-scale single-storey, single-bay RC frames. The frames were identical in geometry and characterised by poor mechanical material properties and steel reinforcement details, promoting the development of a strong-beam-weak-column mechanism. The experiments comprised tests on four specimens: a non-retrofitted masonry-infilled frame employed as a reference specimen and three frames strengthened with CLT panels as infills or externally connected retrofitting elements. The paper presents construction details of the strengthening interventions, demonstrates a step-by-step application procedure, and summarises the main observations from the tests, illustrating the evolution of structural damage, the ultimate failure mode, and the cyclic hysteretic response of the specimens. The experiments showed promising results, proving that both retrofit configurations improved the seismic behaviour of the RC frames considerably. Specifically, the RC-TP and RC-TPext retrofit interventions increased the lateral strength of the reference frame by approximately 169% and 104%, respectively. At the same time, both configurations prevented the shear collapse of the columns.

Experimental Research and FE Model of a Bolted Steel-CLT Composite Connection

Steel-timber composite structures have numerous advantages compared to steel only and timber only structures. One of the most important parts of a composite structure is the composite connection. Object of this research was a steel-CLT composite connection consisting of a steel profile, a cross-laminated timber (CLT) panel and a bolt with nut and washer. Aim of the research was to develop an efficient finite element (FE) model of a bolted steel-CLT composite connection and to validate it experimentally. The research process consisted of several steps: experimental testing of the considered connection using asymmetrical push-out test, numerical modelling and analysis of the connection using Finite Element Method (FEM), validation of the numerical model using experimental results, and parametric study of the proposed numerical model. For numerical analysis, an innovative method for timber modelling has been proposed. The comparison between the experimental and numerical research results demonstrated that the proposed numerical model was convenient for practical application in structure analyses. The parametric study showed that, in some cases, atypical failure modes of the connection occurred. Based on registered behavior, a recommendation is given to calculate the load capacity of the connection integrally, taking into account both the primary (Johansen’s) and the secondary (rope effect) part of the connection strength, instead partially, as proposed by EN standards.

System identification using Bayesian model updating with cross-signature correlations

In this paper, a novel likelihood function for Bayesian model updating algorithms is proposed, in particular for the transitional Markov chain Monte Carlo algorithm. The likelihood function is based on a measure of fit in which the prediction errors between the measured and simulated frequency response functions are evaluated using the cross-signature correlation. This formulation avoids the problem that for the commonly used modal measure of fit, the obtained results are ambiguous (i.e., correlated) when both the mass and stiffness properties are uncertain. Validation is first performed on simulated test data of cross-laminated timber structures and, in a second application, on real experimental data of a cross-laminated timber panel by performing Bayesian model updating on a finite element model of the specimen under consideration.

Study of the hygroscopic properties of three Australian wood species used as solid wood and composite products

The use of engineered wood products and mass timber panels such as cross laminated timber (CLT), glued laminated timber (glulam) and laminated veneer lumber (LVL) is becoming more common, as these products have benefits in terms of environmental credentials and resource utilisation and have the potential to provide faster and more economical construction processes. However, timber exposed to moisture for prolonged periods can degrade biologically, leading to a loss of appearance and decreased mechanical properties. Southern pine, radiata pine and shining gum timber are important forest resources for the Australian timber industry. To date, no in-depth studies on the hygroscopic properties of these species have been carried out from a timber wetting point of view. Consequently, existing literature has a knowledge gap regarding the determination of moisture movement properties in these species that are applicable to numerical modelling when used as solid wood or in the production of engineered wood products (EWPs). The work presented herein will help develop a better understanding of moisture ingress and egress in solid timber and EWPs and provide data for future predictive tools (such as numerical modelling) for moisture management in timber buildings. Samples were prepared from solid timber as well as EWP’s to examine the relationships between glue lines and edge gaps in CLT and multiple glue lines in LVL on moisture movement. As expected, longitudinal permeability was higher than radial and tangential permeability for the species tested. Southern pine samples had higher gas and liquid permeability values than radiata pine and shining gum. CLT with end grain sections including an edge gap had higher gas and liquid permeability than similar sections with glue lines only. LVL sections with 1 glue line had slightly lower permeability values than in samples with 2 glue lines. Gas and liquid permeabilities were lower for LVL samples than a two-layered veneer section without a glue line illustrating the barrier posed by the glue line. The moisture loss parameter during the diffusion testing was higher for LVL ends and CLT ends with edge gaps than face and edge sample sections. The results will be used to develop numerical models for moisture behaviour in solid and composite timber panels when exposed to humidity and free water. It is recommended to conduct additional studies to examine the impact of the adhesive layer and its properties on impeding moisture migration or functioning as a moisture barrier.

Bending behavior and bond analysis on adhesively bonded glulam-concrete panels fabricated with wet bonding technique

In this paper, we report on the effect of adhesive type on the bending behavior of adhesively bonded glulam-concrete composite panels. Steel-reinforced and unreinforced concrete were bonded to glued-laminated timber (GL-24 h) panels with polyurethane (PUR) and epoxy adhesives using the wet bonding technique. The PUR and epoxy adhesives (both were two-component adhesives) were selected to represent brittle and ductile adhesive behaviors. Four-point bending load was applied to glulam-concrete composite panels to investigate their bending behavior. The bending behavior measured includes bending load vs. mid-span deflection, strain distribution at the mid-span of the panel, and strain distribution between the loading point and its adjacent support. These were determined by linear variable differential transformers (LVDTs), strain gauges, and digital image correlation (DIC) technique. The experimental results showed that polyurethane-bonded glulam-unreinforced concrete panels showed similar load vs. mid-span deflection curves to epoxy-bonded glulam-unreinforced concrete panels and epoxy-bonded glulam-reinforced concrete panels. The shear stress, shear deformation, and peel strain analyses at the adhesive bond line showed that debonding at the glulam-concrete interface was more likely to occur for panels bonded with the ductile polyurethane.

Vibration-based numerical identification of effective orthotropic elastic properties for finite element model of cross-laminated timber panel

The influence of non-gluing of narrow surfaces of boards on all effective orthotropic elastic moduli for shell or solid finite element models of cross-laminated timber (CLT) panels is investigated. This lack of gluing leads to discontinuous layers and severe meshing difficulties. The objective of this study is to create an equivalent homogeneous layer and equivalent material properties in this case. Two finite element (FE) models were built for comparison. The first model, using solid elements, is the reference without gluing the narrow surfaces. The second considers homogeneous layers and equivalent material properties. Thanks to an identification process, all the elastic moduli of the model with homogeneous layers are adjusted to minimize the difference in vibration frequencies between the two models. A method is proposed to significantly speed-up the calculation of first derivatives, which are necessary for the identification process. The process was applied for 36 configurations of CLT panels with different geometrical properties (number of layers, width and thickness of boards) within the practical range. Metamodels are proposed to quickly calculate the effective moduli based on the vibration properties of CLT panels. The Verification and Validation methodology was applied to evaluate the performance of the two simplified FE models using the effective moduli.

Modelling the behaviour of heavy and mass timber members subjected to blast loads

This paper presents a numerical study investigating the behaviour of glued laminated timber (glulam) beams and cross-laminated timber (CLT) panels subjected to shock-tube simulated blast loads. A 3D constitutive material model for wood, which accounts for the anisotropic nature of the material as well as high strain rate effects, was implemented into a finite element (FE) model via user subroutine. Utilizing the continuum damage approach for wood, a total of eight failure criteria were used to describe both ductile and brittle failure modes. A total of 23 full-scale experimental test results were used in the validation of the modelling approach. In general, the FE model was found to be capable of capturing the overall failure mode, damage propagation, as well as predicting the resistance curves with good accuracy.

Parametric analysis of the effective flange width of mass timber composite floor panels

Mass timber composites (MTCs), where the webs are typically spaced 750–2000 mm apart, have shown potential in overcoming span limitations of conventional flat slab mass timber floors. However, fundamental research investigating the non-linear stress distribution (i.e., shear lag) in the flanges is required. While this behaviour has been simplified in design for other materials using the concept of an effective flange width (EFW), no guidance exists in international design codes for mass timber composites. In the current study, a parametric analysis was conducted on a mass timber I-beam under positive bending where the effects of web spacing, beam configuration (edge or interior placement), shear connection stiffness, concentrated versus uniform loading, web depth, web width, flange thickness, and flange modulus of elasticity on the EFW, were investigated. The reference section in the finite element model consisted of a glued-laminated timber (GLT) panel for the flanges, a glulam beam web, and a fully composite glued connection between elements.The results have shown that existing design code provisions, even those meant for light-frame wood members, over-estimate the EFW of GLT-glulam I-beams. The web spacing, shear connection stiffness, loading type, flange thickness, and web width were observed to be the most influential parameters on the EFW of GLT-glulam MTCs. Between the upper and lower boundaries of connection stiffness, a sharp increase in the EFW was observed below the point of full composite action due to the section beginning to behave as three separate elements. Although, the decrease in composite action resulted in an overall decrease in the bending stiffness of the section. For GLT-glulam MTCs, the modulus of elasticity (MOE) of the GLT flange was not observed to significantly affect the EFW for high degree of composite action configurations. A small increase in the EFW was observed when the degree of composite action was relatively low. Ultimately, the development of equations for quantifying the EFW of MTCs is key to their increased adoption but requires the expansion of the current study to include other mass timber elements, as well as experimental data investigating the most significant parameters identified herein.

Preliminary State of the Art report on Timber Panel Infills as Retrofit measure in reinforced concrete frames structures in seismic regions

Preliminary State of the Art report on Timber Panel Infills as Retrofit measure in reinforced concrete frames structures in seismic regions

Upgrading of Fire Resistance to Architectural Heritage Escape Route Timber Doors

ABSTRACT Original timber stairwell doors in historic masonry apartment buildings of architectural heritage value can be found in the larger cities of Norway. In Oslo, there are around 4000 such buildings, of which many still hold preserved original stairwell doors. The doors often have glass with decorative patterns in the upper parts, and timber panels on the lower part. Old residential buildings are vulnerable to fire due to the building construction and need fire protection upgrades. The stairwell doors are critical elements to prevent fire spread and to keep evacuation routes safe, so their function and condition are important to the level of fire protection in the building. The research work in this paper aims to find retrofit methods for upgrading the fire resistance of these types of doors so they maintain their integrity and insulating properties for up to 30 minutes, at the same time as they maintain their architectural expression. The upgrades must be as little intrusive and destructive as possible. Intermediate scale tests were carried out in a fire resistance test furnace, using different door configurations. The tests lasted between 30 minutes and 42 minutes, with a thermal exposure from the standard time/temperature curve described in EN 1363–1. The results from the tests showed that 40 mm thick laminated wood could withstand up to 30 minutes of fire exposure, thin timber panels could be upgraded using stone wool and robust gypsum boards type R, and that fire-resistant glass could be mounted on the inside of the original glass in different ways. Visual observations indicate that adding smoke seals inside the door leaf are effective for stopping cold and hot smoke. The solutions presented enables the preservation of the original doors’ architectural design, their historical values and aesthetic character.

Bending and shear performance of a cross-laminated composite consisting of flattened bamboo board and Chinese fir lumber

Bamboo-wood composites are effective for utilizing the mechanical properties of bamboo and fast-growing wood resources. Investigation the application of flattened bamboo in engineering structures provides added value to bamboo resources. This paper analyzes the flatwise bending and shear properties of cross-laminated bamboo and timber (CLBT) panels consisting of flattened bamboo boards and Chinese fir lumber. A three-layer cross-laminated timber (CLT) panel made from Chinese fir lumber was used for comparison. The mechanical properties of the CLBT and CLT panels in the major strength direction were obtained through experimental tests, and theoretical and finite element models were developed to predict the panels’ bending stiffness and strength. The calculated values were compared with the experimental data. The results showed that the failure modes of the three groups of CLBT panels were similar to those of the CLT panel and were predominantly rolling shear and bonding delamination. The bending strength and modulus of the CLBT were higher than that of the CLT. Increasing the number of layers of the flattened bamboo board improved the maximum bending moment and bending stiffness of the CLBT. The bending stiffness and strength of the CLBT/CLT obtained from the finite element model were in better agreement with the static test values than the theoretical model values. The results of this study provie new information for future engineering applications and the structural design of CLBT.

Effect of Alternate Drying Techniques on Cross-Laminated Timber after Exposure to Free-Water Wetting

Cross-laminated timber (CLT) panels are commonly used in mass-timber multistorey constructions due to their prefabrication, construction flexibility, environmental credentials and weight-to-strength ratio advantages compared to competing building materials. However, the long-term durability and service life of these mass timber panels require further understanding of their performance when exposed to free water. Wetting and drying trials were conducted by exposing Radiata pine (Pinus radiata) CLT sections to either free water (pooling on a single surface) or submerged water (all directions exposed) saturation, followed by either ambient or fan drying. The panels exposed to water pooling only reached MC above the FSP up to 40 mm of the panel depth. For submerged panels, the MC reached values above the fibre saturation point (FSP) at depths of 30 to 40 mm penetration on both panel faces. When comparing the ambient and fan-drying panel sections over the same time period, a less uniform MC profile was observed for the ambient drying, whereas the fan-dried panels fell below the FSP faster and with a more consistent MC profile. A complementary study was conducted on a standalone 3.0 × 3.0 m CLT room, where the room was wetted during a simulated pipe burst event. The moisture monitoring of wall and floor panels during fan drying of the room showed that an MC reduction from an excess of 40% to below 20% could be reached in less than 96 h for the panels’ surface; however, the middle sections of the panels dried slower than the surface sections. The CLT structure fan drying required a longer drying time than the CLT sections tested due to the closed sections (overlaps and connected faces) and a lower rate of airflow. The study of drying CLT sections highlighted the product reaching and maintaining MC higher than FSP points and the need for further drying applied to minimise long-term decay development. Further study is recommended to investigate the effects of closed sections (connected faces) and the duration of drying needed for semi-finished and finished buildings.

A layered beam-based model for analyzing the stress of rolling shear for the cross-laminated timber panels under out-of-plane bending

When used as horizontal components to carry vertical loads, such as floors and beams, the design of cross-laminated timber (CLT) panels is driven by out-of-plane bending. In this case, rolling shear is always one of the major concerns that governs the performances of ultimate limit state of CLT members. Analytical models are available for predicting the shear capacity of CLT panels, but they are computational extensive and cannot provide the longitudinal distribution of shear stress which is necessary to predict where the failure will happen. In this paper, a layered beam-based analytical model, for analyzing the stress of rolling shear for transversely loaded CLT members was developed. The model deems that the shear deformations of out-of-plane bending CLT members are carried by cross layers while the deformations of bending moment are carried by parallel layers. Based on the layered beam theory, the equation that governs the stress of rolling shear and its analytical solution were derived. It was found that the shear stress distribution in CLT longitudinal direction obeys exponential law and the maximum shear stress is located at the end of the CLT member. Formulas to predict the shear capacity for 3- and 5-layer CLT panels under out-of-plane bending were obtained. The proposed method was validated by the experimental data generated by the authors and by other researchers. Comparing to the shear analogy method and Gamma method, the proposed method requires less computational work and provides similar accuracy.

Assessment of termite damage in cross-laminated timber sections using micro-computed tomography and vibration analysis

The durability of engineered wood products (EWPs) is a parameter yet to be fully investigated and understood. This is specifically important for mass timber structures and cross-laminated timber (CLT) panels. The effect of termites and scale of damage on radiata pine sawn boards have been previously investigated. However, the effects of glue line and the layered structure of CLT exposed to termite feeding in the field in Australia have not been studied. A total of 420 CLT specimens with different exposed faces and layer arrangements were exposed to termite attack in the field. Microcomputer tomography and vibration analysis were used to assess sample conditions before and after 20 weeks exposure. The observed changes showed damage patterns within samples where a glue line and different growth ring patterns were present. The termites created continuous damage along the longitudinal cells through the length and width of the samples. The 3D data showed that the edge gap on the face of panels could potentially act as a pathway for termites entering the core or mid-layers of the panel. The vibration frequency values were lower for samples after the termite exposure. The vibration analysis results showed significant effects of sample direction exposed to termite attack, and percentage of mass loss had significant effects on internal friction and damping values determined.

Experimental Assessment of Alternative Shear Connections in Cross-Laminated Timber-Concrete Floor Systems

New building code changes enable mass timber panels (MTP), including cross-laminated timber (CLT), to be used in moderate and tall buildings as a floor system, usually with a concrete topping. A floor system of CLT composite with a reinforced concrete topping slab can provide increased stiffness and strength, making the system more advantageous. Present connection methods used to produce composite action within timber-concrete composites (TCC) have limitations when considering constructability or performance. This study presents experimental results from four (4) shear connectors for CLT-concrete composite floor systems, including three developed for this study. The connectors included self-tapping screws (STS) at 45-degrees, a modified lag screw with an integral plate washer that bears on the CLT surface at installation, a steel angle anchored only at the end of the span, and an inverted-T steel section with stem perforations. Different tests were performed on the different connectors including individual fastener tests, push-off group tests, and full-scale one-way bending tests. The push-off group tests showed that the proposed washer-screw exhibited higher stiffness and strength than a conventional STS. The full-scale one-way bending testing showed that the STS specimen exhibited the lowest strength of the alternatives. The inverted-T section exhibited the highest stiffness, while the other three connections had similar stiffness to the STS.

Moisture- and mould-resistance: multi-modal modelling leveraging X-ray tomography in edge-sealed cross-laminated timber

Edge-sealing, which involves treating the edges of wood products, improves water resistance. This study investigated the feasibility of edge-sealed cross-laminated timber (CLT) panels to reduce capillary water uptake, thereby resisting mould formation. The water and vapour permeabilities of ten characteristically different single-layer sealant coating systems were systematically determined. Multi-modal assessment leveraged by computed tomography (CT) scanning methodology was used to enhance detection of material characteristics beyond the standard coating permeability assessment. Moisture content was observed to change during the specimens’ absorption and desorption depending on the sealant system applied. The results revealed different characteristics of coatings during the water absorption and desorption stages. Findings from this study were used to develop recommendations regarding the water resistance of coating systems, curing time, susceptibility to mould formation, and industrial applicability. Results suggest that edge-sealed CLT could minimise the risk of mould formation, which can occur at worksites with minimal weather protection. The method developed in this study provides a basis to evaluate new coating systems and determine which use case is the best for a particular coating type. This study also incorporates insights from industry to identify future research orientations, which may pave the way for new designs and assessment techniques.

Application of the wave and finite element method to predict the acoustic performance of double-leaf cross-laminated timber panels

This paper presents a wave and finite element method for predicting the sound transmission loss of double-leaf walls comprising panels of arbitrary complexity separated by a cavity which can contain air or an insulating material. The method is verified against analytical models and validated against a number of different experimental measurements. The method is then used to investigate the effect of various parameters on the sound transmission performance of a double-leaf cross-laminated timber (CLT) wall construction. Parameters investigated include the flow resistivity of the insulating layer separating the wall panels and the effect of panel thickness and orientation. The effect of a neoprene rubber layer in between the CLT panels is also investigated.