Timber Plates Research Articles

Short cross-laminated timber plates subjected to out-of-plane loads

The use of cross-laminated timber (CLT) panels has increased significantly, driven by the demand for more sustainable structural solutions. When used in short spans, the load capacity of CLT panels can be significantly enhanced; however, their behaviour and failure mechanisms differ from those of large spans. This study evaluates the mechanical behaviour of short-span CLT panels made from Pinus taeda L. under out-of-plane loads, through experimental analyses on full-scale panels. Fourteen industrially manufactured panels were tested in four-point bending tests, using adhesive weights of 250 and 220 g/m². The values of maximum bending moment, shear force, and their respective resistances were analysed based on the observed failure modes. The transverse modulus of elasticity was determined using strain gauges. It was found that short panels, with a span-to-depth ratio of 9 ≤ l/h ≤ 12, exhibited bending moment and shear force failures, with no significant differences between adhesive weights. Discrepancies in shear resistance and stiffness values compared to existing standards suggest the need for reduced-specimen testing for greater accuracy.

A dynamic stiffness method to estimate the sound insulation of an arbitrarily installed thick cross laminated timber (CLT) plate

There is no generally accepted standard methodology to determine the dynamic constants of whole cross laminated timber (CLT) plates. Combined with the observation that CLT walls or floors are installed in situ under very different conditions to laboratory measurement conditions a methodology is sought to determine the sound insulation of CLT plates installed under arbitrary conditions without accurate information concerning the dynamic constants (and boundary conditions). The methodology may have applications where a panel can be tested in situ e.g. in pre-completion testing. In the laboratory measurement a CLT plate was mounted on the laboratory floor on two wooden joists placed at arbitrary positions to support the weight of the plate to represent a possible installation in situ.

Modelling the fire resistance of cross‐laminated timber rib panels

AbstractA 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.

Structural Analysis of the Sympathetic Restoration and Conservation of the Gopinath Temple, Kathmandu, Nepal

The sympathetic restoration and conservation of built cultural heritage play a significant role in the management and preparedness for future climate scenarios by facilitating adaptive reuse, enhancing cultural resilience, preserving traditional knowledge, and boosting tourism. The importance of restoring damaged heritage sites after an earthquake drew international attention to Nepal after the 2015 Gorka Earthquake. UNESCO established an office in Kathmandu to promote the restoration of tangible and intangible heritage in the area. This included developing structural analyses of buildings with historical and cultural value that, due to their nature, cannot be intervened with the same methodology as modern buildings. In this paper, the case study of the earthquake-damaged Gopinath temple is discussed. First, an initial visual inspection phase and the following diagnosis of the structure are discussed. Then, the results from a series of static and dynamic structural analyses performed to determine the safety level of the structure, together with a sensitivity analysis, are presented. A sympathetic intervention proposal capable of increasing the temple’s safety level, and based on the addition of timber plates, has resulted in substantial improvements in the lateral behavior of the structure. The proposed intervention is deemed sustainable and able to increase the resilience of the temple in the face of future hazards.

A finite element for static and dynamic analyses of cross-laminated timber floors

In this paper, a finite plate element for floorings consisting of a cross-laminated timber slab and a floating floor based on linear elastic behavior is presented. Both elemental mass and stiffness matrices are derived, allowing for static and dynamic analyses. For the cross-laminated timber plate, a higher order plate theory is employed, capturing the layer-wise zig-zag deformation of the plate and the stresses derived thereof accurately. It is augmented by an elastic layer representing the footfall sound insulation and an isotropic plate modeling the screed of a floating floor. In total, the finite element exhibits ten nodal degrees of freedom. Hence, larger structures can be analyzed efficiently, which is demonstrated by comparative finite element simulations with a commercial software package based on continuum elements.

The effect of thickness of transverse and longitudinal layers on deformability and stress distribution in three-layer panels made of cross-laminated timber

Introduction. The key feature of timber and materials, made from it, is anisotropy, or a pronounced difference between mechanical properties manifested in different directions. The construction of a cross-laminated timber plate, or a CLT panel, ensures its high strength and rigidity due to the perpendicular arrangement of fibers in mutually perpendicular layers. The article examines the effect of thickness of transverse and longitudinal layers on deformability and stress distribution in three-layer CLT panels. The relevance of the work lies in the need to obtain computational data for analyzing changes in strength characteristics of panels to select the most effective panel configuration.
 
 Materials and methods. Due to the lack of a standardized testing methodology, SCAD+ software package was applied to conduct the studies using numerical methods. The design scheme is identified as a general system whose deformations and principal unknowns are represented by linear displacements of nodal points along the X, Y, Z axes and rotations around these axes. A three–layer plate was selected as the element to be analyzed, the outer layers of which are longitudinal, and the inner one is transverse. Its simplified design scheme is a hinged beam.
 
 Results. The results of the study and calculations made using SCAD+ were applied to make tables and graphs showing dependence of deflection, distribution of normal and shear stresses on thickness of transverse and longitudinal layers of timber.
 
 Conclusions. The data, obtained by the authors, allow evaluating the effect of thickness on deformability and stress distribution in three-layer CLT panels to select the effective design. A change in thickness does not always bring a large difference between mechanical properties, which allows optimizing the panel parameters. The significance of the research lies, among other things, in expanding the scientific and engineering knowledge of timber structures.

Dilatation wave velocities estimated from the plateau in sound insulation of cross-laminated timber (CLT) plates

There are four inherent problems when predicting the airborne sound insulation of cross-laminated timber (CLT) plates. (1) The internal loss factor of wood products is high and therefore difficult to measure using the structural reverberation time technique. (2) Solid wood is a low-density building material compared to reinforced concrete or masonry construction. (3) Timber is orthotropic. (4) Orthotropic behaviour includes low shear moduli. CLT plates, similarly to thick masonry or concrete plates, exhibit thick plate behaviour in the high frequency range (f>1600Hz). The high frequency sound insulation data of nine plates is examined. Transitions to a thick plate seems to occur in all measurements. However, a clearly observable plateau is only visible for six of the nine plates. Simple methods are applied to extract information about the CLT plates from this high frequency (f>1600Hz) measured data. The data extracted from the plate is compared to typical values for equivalent isotropic plates, where the bending stiffness is assumed to be B_iso=√(B_x B_y ). The results are discussed in the context of laboratory measurement of sound insulation.

Design considerations for robotically assembled through-tenon timber joints

This research investigates the robotic assembly of timber structures connected by wood–wood connections. As the digitization of the timber construction sector progresses, digital tools, such as industrial robotic arms and Computer Numerical Control machines, are becoming increasingly accessible. The new-found ease with which wood can be processed stimulates a renewed interest in traditional joinery, where pieces are simply interlocked instead of being connected by additional metallic parts. Previous research established a computational workflow for the robotic assembly of timber plate structures connected by wood–wood connections. This paper focuses on determining the physical conditions that allow inserting through-tenon joints with a robot. The main challenge lies in minimizing the clearance between the tenon and the mortise in order to keep the connections as tight as possible. An experimental protocol has, therefore, been developed to quantitatively assess the performance of the insertion according to different geometric parameters. Robotic insertion tests have been carried out on over 50 samples of 39 mm Laminated Veneer Lumber. Results showed the interest of tapering the joint with a 5 degrees angle, in addition to introducing an offset of 0.05 mm, to minimize friction forces during the insertion. This configuration was confirmed by successfully assembling a 2,50 m long box girder with the same parameters.

Residual stresses in adhesively bonded wood determined by a bilayer flexion reporter system

The application of adhesives in modern timber engineering often introduces moisture into the wood, leading to permanent residual stresses after hardening. This paper proposes a novel approach to assess these residual stresses by using wooden bilayers as a reporter system. For thin bilayers, moisture-induced stresses lead to pronounced visible flexion that can be used to identify the stress-driving parameters of the adhesive’s gelation process. These parameters depend solely on the wood/adhesive combination and are inversely determined by fitting a finite element method model on the experimentally obtained flexion state. In a subsequent step, the determined parameters are used to calculate the residual stresses in the adhesive bondline of cross-laminated timber plates, emphasizing this approach’s scale independence and general applicability to larger scale structures. All combinations of European beech and Norway spruce with the adhesives Melamine–Urea–Formaldehyde (MUF), Phenol–Resorcinol–Formaldehyde (PRF), and Polyurethane (PUR) were investigated.

Seismic behavior of variable friction timber dampers: Experimental and numerical investigation

This paper proposed variable friction timber dampers (VFTDs) made of replaceable grooved timber plates, seismic behavior of such dampers and its influence on the lateral performance and dynamic response of heavy timber frames were investigated. Firstly, in total four specimens with different geometry characteristics and pre-stressing forces were conducted with reversed cyclic loading test. Typical damage and failure modes were identified and hysteretic curves were analyzed. Secondly, a modelling method on the hysteretic behavior of VFTDs was proposed by using multiple materials in OpenSees. Combined an existing test of a simple timber frame, the lateral performance and dynamic response of timber frames with VFTDs were numerically investigated and compared to those of a simple frame and a frame with a conventional friction timber damper. The experimental results indicated that timber plates of VFTDs cracked perpendicular to wood grain under combined compression and friction. The cracking weakened the integrity of timber plates, resulting to asymmetry of hysteretic curves of VFTDs. VFTDs were able to dissipate energy meanwhile provide higher damping force when timber plates slid on slope surfaces. Increasing pre-stressing force in a certain range considerably improved damping force and energy dissipation capacity of VFTDs. The numerical simulation demonstrated that VFTDs increased the lateral load-resisting capacity and energy dissipation capacity of timber frames more than 55% and 710%, respectively. Owing to superior lateral load-resisting capacity and extraordinary energy dissipation capacity of VFTDs, the peak drift and acceleration of timber frames decreased up to 55%. VFTDs with slope sliding surfaces outperformed VFTDs with consecutive flat and slope sliding surfaces and conventional friction timber dampers in seismic response reduction.

Structural Performance of Cross-Laminated Timber Plates in Bending: An Experimental and Numerical Approach

Structural Performance of Cross-Laminated Timber Plates in Bending: An Experimental and Numerical Approach

Investigation of rolling shear properties of cross-laminated timber (CLT) and comparison of experimental approaches

The structural behaviour of a cross laminated timber (CLT) system is dictated in-part by the rolling shear properties (both strength fr and modulus Gr) of its laminates. To investigate the rolling shear properties of CLT, short-span four-point bending tests, modified planar shear (MPS) tests with timber sandwich plates, and MPS tests with steel sandwich plates were conducted on Australian grown Eucalyptus nitens and radiata pine, as well as European grown Norway spruce. A strong positive relationship between aspect ratio and strength was found, which agrees with previous research. However, the annual ring orientation distribution rather than the aspect ratio was shown to have the most pronounced effect on the shear modulus. The load direction, which has not been accounted for by researchers, was shown to have a substantial effect on the measured rolling shear strength. When the applied load direction was parallel to the annual rings, the Eucalyptus nitens, radiata pine and Norway spruce specimens exhibited rolling shear strengths of 4.1, 2.7 and 1.7 MPa respectively. These average recorded strengths were found to decrease by 16%, 40% and 52% respectively when the load direction was changed to run perpendicular to the rings instead. By directly measuring the shear deformations of two specimens tested under different MPS approaches using Digital Image Correlation (DIC), the impact of the plate material on the recorded shear modulus was isolated. This revealed that the MPS tests with steel plates recorded average rolling shear modulus values which were as much as 42% higher than their counterparts with timber plates, as well as identifying substantial errors in laser and LVDT-like measurement tools. It is recommended that a DIC approach is employed to complement or replace a UTM or laser sensor deformation measurement approach to mitigate these potential errors.

Bayesian parameter updating in linear structural dynamics with frequency transformed data using rational surrogate models

The identification of parameters of structural models through measurements of the system’s response is of interest in many contexts. In Bayesian system identification the underlying inverse problem is formulated in a probabilistic setting, and Bayes’ rule is applied to update a prior conjecture on the parameters. We apply the Bayesian framework to identify the parameters of structural systems using dynamic measurement data. The likelihood function is formulated in terms of the misfit of the frequency transformed data and the model frequency response function. We introduce a novel formulation that accounts for the correlation of the model error in both spatial and frequency domain. The proposed formulation is able to handle dense data sets in the frequency domain without need to manually select data points. Due to the high computational demands of sampling-based approaches for solving the Bayesian updating problem with expensive structural dynamics models, we resort to surrogate models. We apply a recently introduced rational surrogate model that approximates the complex frequency response as a rational of two polynomials with complex coefficients. Samples of the posterior distribution of the model parameters are then obtained through an adaptive sequential sampling approach using the surrogate instead of the original dynamic model. The proposed method is successfully applied to identify the orthotropic stiffness and damping parameters of a finite element model of a cross laminated timber plate.

Determination of the dispersion relation in cross-laminated timber plates: Benchmarking of time- and frequency-domain methods

The availability of a reliable estimate of the dispersion relation of plates is of great importance for acoustic modelling. Several experimental methods for the extraction of wavenumber and wave velocity information are discussed in the literature. They differ, among other factors, by the sensitivity to noise and multiple reflections, frequency range of application and implementation of the processing algorithm. While for homogeneous thick or thin plates well-established analytical solutions are available, non homogeneous materials would benefit from experimental characterisation. In this framework, our attention is focused on cross-laminated timber (CLT) elements, load-bearing orthotropic layered wood plates that revolutionised the sector of timber construction. The anisotropic and non homogeneous nature of wood suggested testing methods that, though converging for homogeneous materials, could bring different results in their application to CLT elements. The aim of this paper is therefore to benchmark methods for the extraction of wavenumber information on CLT plates, from which the effective elastic properties to model CLT structures as an equivalent homogeneous plate can be derived. This is achieved through a numerical and experimental benchmark of well-established methods for the evaluation of the real component of the propagating wavenumber in CLT elements. Five relevant methods were selected through a literature review, implemented and analyzed: three in the time domain, namely maximum peak, cross-correlation and kurtosis, and two in the frequency domain: phase difference and wave correlation. First, the five methods were benchmarked by numerical simulation on a homogeneous material. In this ideal case, results showed to be consistent for all methods. Then, wavenumber measurements were performed on a cross-laminated timber plate. The results show that the maximum peak, cross-correlation and the wave correlation method provide the lowest dispersion of the data. Considering the time required by the installation of the setup, the wave correlation method seems to be the best alternative among the proposed ones.

Experimental analysis of cross-laminated timber rib panels at normal temperature and in fire

The results of an experimental programme on the structural behaviour, fire behaviour, and fire resistance of CLT rib panels are presented. The floor system consists of cross-laminated timber (CLT) plates rigidly bonded to glued-laminated timber ribs by means of screw-press gluing.The experimental programme comprised ultimate-load tests at normal temperature as reference tests and full-scale fire resistance tests on four cross-sections. In addition to the reference tests, shear tests of the glue line between CLT plate and glued-laminated timber rib were performed for analysis of the cross-sections’ composite action.The results of the reference tests show good agreement with results based on the simplified method according to EN 1995-1-1 [1] and its final draft of CLT design [2]. The importance of the glue line’s quality was confirmed. The fire resistance tests show results on the safe side compared to predictions of the fire behaviour according to EN 1995-1-2 [3] and its actual draft [4]. However, the fire resistance was underestimated due to conservative assumptions about the composite cross-section’s structural behaviour.The experimental programme addressed the fire behaviour and fire resistance of CLT rib panels currently not covered in standards. The project’s overall aim is the development of design rules in fire for EN 1995-1-2.

An integrated design tool for timber plate structures to generate joints geometry, fabrication toolpath, and robot trajectories

This paper presents an integrated design tool for structures composed of engineered timber panels that are connected by traditional wood joints. Recent advances in computational architecture have permitted to automate the fabrication and assembly of such structures using Computer Numerical Control (CNC) machines and industrial robotic arms. While several large-scale demonstrators have been realized, most developed algorithms are closed-source or project-oriented. The lack of a general framework makes it difficult for architects, engineers and designers to effectively manipulate this innovative construction system. Therefore, this research aims at developing a holistic design tool targeting a wide range of architectural applications. Main achievements include: (1) a new data structure to deal with modular assemblies, (2) an analytical parametrization of the geometry of five timber joints, (3) a method to generate CNC toolpath while integrating fabrication constraints, and (4) a method to automatically compute robot trajectories for a given stack of timber plates.

Computational simulation of light timber framing connections strengthened with self-tapping screws

Traditional light timber framing systems, comprised of stud to top and bottom plate connections, suffer from relatively low stiffness along compression perpendicular-to-grain of the plates, leading to excessive shortening of studs in mid-rise buildings. Experimental testing of timber stud to plate connections revealed that a reinforcement technique employing self-tapping screws, placed at the top/bottom plate interface, was an efficient way to enhance the connection stiffness and alleviate permanent displacements. In other words, the combination of bonding stress development at the interface of self-tapping screws and timber stud as well as plastic deformation, built up in timber plate in compression perpendicular-to-grain, plays an important role in improving the bearing stiffness/strength of these connections. In this paper, structural performance of light timber framing connections, strengthened with self-tapping screws under gravity loading is investigated, utilising finite element modelling. Continuum damage mechanics framework along with traction-separation cohesive zone technique are incorporated in detecting various failure scenarios and damage propagation for timber components in the finite element modelling. Small-scale unreinforced and reinforced stud to top/bottom plate connections using the Machine Graded Pine timber and high strength self-tapping screws were employed and tested experimentally to calibrate the finite element modelling parameters. Calibrated parameters are then utilised to establish a full-scale light timber framing finite element model. It is demonstrated that finite element models established in this paper can predict the load-displacement response and failure modes of reinforced light timber framing systems.

Three-Dimensional Numerical Calculation Model for Static Behavior Simulation of Cross-Laminated Timber Plates under Thermal Environment

Cross-laminated timber (CLT) is well known as an interesting technical and economical product for modern wood structures. The use of CLT for modern construction industry has become increasingly popular in particular for residential timber buildings. Analyzing the CLT behavior in high thermal environment has attracted scholars’ attention. Thermal environment greatly influences the CLT properties and load bearing capacity of CLT, and the investigation can form the basis for predicting the structural response of such CLT-based structures. In the present work, the finite element method (FEM) is employed to analyze the thermal influence on the deformation of CLT. Furthermore, several factors were taken into consideration, including board layer number, hole conformation, and hole position, respectively. In order to determine the influence, several numerical models for different calculation were established. The calculation process was validated by comparing with published data. The performance is quantified by demonstrating the temperature distribution and structural deformation.

A framework to automate the design of digitally-fabricated timber plate structures

The current study uses knowledge from digital architecture, computer science, engineering informatics, and structural engineering to formulate an algorithmic framework for integrated Computer-Aided Design (CAD) and Computer-Aided Engineering (CAE) of Integrally-Attached Timber Plate (IATP) structures. The algorithm is designed to take the CAD 3D geometry of an IATP structure as input and automates the construction and analysis of the corresponding CAE model using a macroscopic element, which is an alternative to continuum Finite Element (FE) models. Each component of the macro model is assigned a unique tag that is linked to the relevant geometric and structural parameters. The CAE model integrity is maintained through the use of the common data model (CDM) concept and object-oriented programming. The relevant algorithms are implemented in Rhinoceros 3D using RhinoCommon, a .NET software development kit. Once the CAE macro model is generated, it is introduced to the OpenSees computational platform for structural analysis. The algorithmic framework is demonstrated using two case structures: a prefabricated timber beam with standard geometry and a free-form timber plate arch. The results are verified with measurements from physical experiments and FE models, where the time needed to convert thousands of CAD assemblies to the corresponding CAE models for response simulation is considerably reduced.

Macroscopic Model for Spatial Timber Plate Structures with Integral Mechanical Attachments

AbstractThe use of integral mechanical attachments (IMAs) in spatial free-form timber plate structures has been revitalized by the production of engineered boards and recent developments in digital...