Timber Panels Research Articles

PROPRIEDADES DA MADEIRA LAMINADA CRUZADA COLADA COM ADESIVO À BASE DE TANINOS DA CASCA DAS ÁRVORES DE Mimosa Tenuiflora

ABSTRACT This study aimed to determine the concentration of condensed tannins in the bark of Mimosa tenuiflora (Willd) Poir trees. Additionally, the physical-mechanical properties of cross-laminated timber (CLT) panels bonded with an adhesive based on M. tenuiflora tannins were assessed. Bark was collected from five trees. The adhesive formulation was synthesized by mixing powdered tannins, paraformaldehyde, and water at 50 °C under continuous stirring. Bark tannins extract in its pristine state without any previous chemical treatment or modification was employed to synthesize the adhesive. Viscosity, pH, solids content, and gel time of the adhesive formulation were determined. CLT panels were manufactured with Eucalyptus spp. wood. The bonding performance was assessed by determining the physical (apparent density and water absorption) and mechanical (modulus of elasticity – MOE, modulus of rupture – MOR, and shear strength) properties of the CLT panels. Condensed tannins content in the M. tenuiflora bark was 23.4%. Adhesive properties were pH = 3.93, TS of 50.64%, gel time of 460 s, and 6,000 cP for viscosity. Values of MOE, MOR and shear strength were 4,411, 16.18, and 1.06 MPa, respectively. The M. tenuiflora tannins are promising for the formulation of adhesives to bond CLT.

Behavior of timber-concrete composite with defects in adhesive connection

Rigid timber to concrete connection is the most effective solution for timber-concrete composite members subjected to the flexure which provides full composite action and better structural behaviour. One of the most used technologies to produce glued connection of the timber-concrete composite is “dry” method, which includes gluing together of timber and precast concrete slab. This technique has high risk of forming a poor-quality rigid connection in timber-concrete composite, and there are difficulties in controlling the quality of the glued connection. The effect of the non-glued areas in connection between composite layers on the shear stresses and energy absorption were investigated by finite element method and laboratorian experiment. Three timber-concrete composite panels in combination with carbon fibre reinforced plastic composite tapes in the tension zone with the span 1.8 m were statically loaded till the failure by the scheme of three-point bending. Mid-span displacements were measured in the bending test. One specimen was produced by dry method, by gluing together cross-laminated timber panel and prefabricated concrete panel. Timber-concrete qualitative connection of the other two specimens was provided by the granite chips, which were glued on the surface of the cross-laminated timber by epoxy, and then wet concrete was placed. Dimensions of the crushed granite pieces changes within the limits from 16 to 25 mm. The investigated panel with different amount and sizes of non-glued areas in the timber to concrete connection was numerically modelled. Obtained results shown, that the increase of shear stresses is influenced not so much by a total amount of non-glued areas, but by the size of the individual defective areas. Moreover, large non-glued areas significantly reduce the energy absorption of elements subjected to the flexure, which was observed experimentally for defective panel produced by the classical dry method with almost 4 times larger mid-span displacements than for panel with full composite action provided by the proposed production technology of the timber to concrete rigid connection. So, the proposed technology based on the use of granite chips, provides a high-quality connection between timber and concrete layers, with insignificant ration between possible defect and total connection surface area, which is equal to the area of ​​one granite chips edge.

Improved seismic response of light-frame-timber panels with cement-particle-board sheathing of various thicknesses and different configurations of fasteners

Due to their comparable fire characteristics and surface preparation, light-frame timber panels using cement-particle boards (CPB) as a sheathing material present a potential alternative to gypsum-fibre boards. An experimental campaign was conducted to evaluate the behaviour of CPB light-frame-timber panels under in-plane lateral loading. Monotonic and cyclic in-plane shear tests were conducted on full-size panels, following preceding tests on the stapled sheathing-to-timber connections used in the panels. The influence of the boards’ thickness and staple geometry on the response of connections and panels was studied, also on panels with an asymmetrical CPB layout, which proved not to have a negative influence on the panels’ lateral load-bearing capacity. Furthermore, in order to improve the seismic response, panels, which had almost twice the number of staples compared to the basic panel, were tested; one variation with two rows of staples, and the other with the staples spaced closer together, such that the spacing distance was halved. The tests revealed a significant, though not proportional, increase in lateral resistance in the strengthened panels. Fastening the CPB with two rows of staples proved the better option, since subsequent failure of the CPB along the connections, as opposed to ductile failure of the staples in the basic panels, proved not to reduce the panels’ deformation capacity. The paper also compares the test results of the connections and panels to analytical results according to Eurocode 5 (EC5), the European code provision for the design of timber structures.

CLT concrete composite floors with steel kerf plate connectors

This paper presents experimental investigations on timber-concrete-composite (TCC) floors with transversely installed steel kerf plates as shear connectors. The TCC system was comprised of 245 mm thick, 7-ply cross-laminated timber (CLT) panels with 150 mm concrete topping. Three embedment depths of the steel kerf plates in CLT (35 mm, 70 mm, and 90 mm) were evaluated at hand of 18 small-scale shear tests. It was shown to be beneficial to only engage the top layer of the CLT panel in order to avoid rolling shear failure. Subsequently, two full-scale TCC floor segments were tested under symmetric four-point bending. The tests confirmed that the TCC floors with steel kerf plates can be designed using the established gamma procedure, and that they exhibited adequate capacity and stiffness to provide an economical solution. The results from this research were utilized to make project-specific design decisions for “The Arbour”, a 10-storey mass timber building for George Brown College, located in Toronto, Canada.

Evaluation of Low-Grade Yellow-Poplar (Liriodendron tulipifera) as Raw Material for Cross-Laminated Timber Panel Production

Abstract Utilization of low-grade yellow-poplar (Liriodendron tulipifera) lumber would provide for alternative structural lumber sources and promote the growth of cross-laminated timber (CLT) manufacturing facilities within the Appalachian Region. A significant amount of low-grade yellow-poplar lumber (i.e., National Hardwood Lumber Association [NHLA] No. 2A and Below Grade) is utilized for wood pallets. In practice, this material is not graded for structural purposes. Additionally, research on yellow-poplar for structural use has focused on grading lumber from a small population of selected logs, not by regrading NHLA lumber from manufacturing facilities. Therefore, the research's objective was to investigate the structural grades of a typical population of NHLA graded No. 2 and lower lumber and evaluate their potential to meet structural grades necessary for CLT panels. NHLA graded lumber was regraded and assigned to visual structural grades following Northeastern Lumber Manufacturers Association rules and evaluated for flatwise bending modulus of elasticity (MOEb) by nondestructive proof loading. The results of the study indicated that 54.6 percent of the boards possessed a minimal structural visual grade required for CLT panels according to American National Standards Institutes/The Engineered Wood Association (ANSI/APA) PRG 320-2019 (2020). Splits were the most common limiting defect that downgraded boards to nonstructural grades. Also, 96.6 percent of the boards evaluated had a MOEb above the required minimal board value of 1.2 ×106 psi (8,274 MPa) listed in ANSI/APA PRG 320-2019 (2020). The results of the study indicated that a majority of NHLA low-grade yellow-poplar, when regraded for structural purposes, meets or exceeds minimum lumber grade values necessary for use in CLT panel production.

Non-Destructive Assessment of the Elastic Properties of Low-Grade CLT Panels

The use of cross-laminated timber panels (CLT) made of low-grade structural timber has steadily increased in developing countries. These panels usually present several natural defects, which can cause a high local variation of their orthotropic elastic properties, generating future structural serviceability problems. Our work aims to estimate the local variability of the elastic properties in low-grade CLT panels by combining nondestructive transverse vibration testing, numerical simulations, and regional sensitivity analysis (RSA). Four three-layer Radiata pine CLT panels were subjected to transverse vibration tests with supports at four points. Besides, a series of numerical simulations of the panels, considering the local variability of the elastic properties of the panels in eight zones, were carried out using the finite element method. Then, RSA analysis was performed to study in which ranges of values the panels’ elastic properties generated lower differences between the measured versus simulated dynamic properties. Finally, a structural quality control indicator was proposed for the CLT panels based on keeping low the probability that the elastic properties in the central zones do not exceed minimum acceptable values. The results obtained suggest that the proposed methodology is suitable for segregating CLT panels with high concentrations of defects such as pith presence.

Structural performance of composite WikiHouse beams from CNC-cut timber panels

Computer-numerical-control (CNC) fabrication of interlocking-plate timber structures is a promising form of construction for housing with the potential to be socially, economically and environmentally sustainable. The primary mechanisms of load transfer in these structures rely on direct contact and friction between interlocking elements, without the nails and screws used in conventional timber structures. The development of these connections is relatively new, and therefore the application of interlocking plates structural systems in real projects is so far limited. In this study, the WikiHouse interlocking-plate timber structural system for digitally fabricated houses is presented from a design and fabrication point of view. The main structural elements of the system, the beams and columns, are hollow section members fabricated using computer-numerical-control (CNC) cut plywood panels. In the first part of the paper, the concept of Wikihouse and its fabrication process are presented. Then, the performance of the structural beams is investigated by means of experimental testing on full scale 5 m specimens. Finally, an analytical model to calculate the beam capacity and displacements is derived based on elastic beam bending and joint flexibility. Results show that the specimens failed in a ductile manner. Furthermore, it was found that the joints between the panels introduce extra flexibility to element, and that rigid-body rotations occurring in the joints within the span make a substantial contribution to the overall deflection.

Mechanical behavior of V-shaped timber folded-plate structure joints reinforced with self-tapping screws

Timber folded-plate structures built with cross-laminated timber (CLT) panels can be applied to gymnasiums and conference halls. The design of the joints is crucial to facilitate the development of timber folded-plate structures. Considering that the compressive performance of CLT panels should be fully utilized and the failure of the joints was induced by the self-tapping screws, 45° miter-connected (MCJR) and mortise-tenon (MTJR) joints reinforced with self-tapping screws were designed. Eight CLT specimen groups with varying connection type, loading direction, and self-tapping screw spacing and diameter were designed and subjected to tests. Typical characteristics of the failure modes and moment–rotation curves were evaluated, and the corresponding rotational stiffness, yield rotation, yield moment, ultimate rotation, and ultimate moment of the specimens were calculated. The results showed that the failure mode of the MCJR and MTJR in push was the pull-out of self-tapping screws, and those in pull included the shear-off and pull-out of self-tapping screws. The loading direction significantly influenced the rotational stiffness and ultimate moment of both types of joints. The mechanical behavior of the MTJR in pull was better than that of the MCJR in pull; however, the rotational stiffness and ultimate moment of the MTJR in push were relatively lower than those of the MCJR in push. Moreover, increased self-tapping screw diameter and decreased self-tapping screw spacing significantly improved the mechanical behavior of MCJR. Finally, an analytical model was established to determine the rotational stiffness of the MCJR and MTJR in different loading directions. A comparison of the analytical and experimental results demonstrates that the proposed analytical method can conservatively estimate the rotational stiffness of the MCJR and MTJR.

Application of Variability Response Function to Cross Laminated Timber

Variation in material properties leads to variation in stiffness, or displacement response, of structural systems. This paper presents an efficient method to calculate the variability in stiffness of a three-layer Cross Laminated Timber (CLT) panel as a result of heterogeneous elastic properties in the constituent lumber. Typically, problems involving stochastic material properties are solved by Monte Carlo simulations, which is computationally expensive for complex systems. The Variability Response Function is a well-established concept for efficient evaluation of the variance of stochastic systems where properties are modeled by random fields. A new method to study the variation in CLT panel stiffness is developed by applying the Variability Response Function to CLT geometry. Using this method, novel CLT panel layups can be efficiently studied, increasing opportunities for traditionally low-value species to be used in CLT panels. Three case studies are provided to demonstrate the application and utility of the developed method.

Experimental and numerical investigations of a timber-concrete dovetail splice joint

Cross-laminated timber panels offer an effective option for timber structures; they allow biaxial load transfer and have good dimensional stability. However, practical transportation and handling limits size of the panel and a stiff connection between the panels is required to effectively utilise biaxial properties. In this paper, a dovetail splice joint for timber panels is presented using cross-banded LVL with cast concrete grout interlayer. The interlayer allows a tight fit, which is important for stiffness, but also avoiding installation problems due to manufacturing tolerances and moisture-induced dimensional changes. The mechanical behaviour of the dovetail joint was investigated experimentally for various geometries. Furthermore, a numerical model was developed that shows a wide agreement with the experiments, especially in the cases with governing failure in the LVL. Using the numerical model, a parameter study was performed where the influence of the connection length (number of dovetails) and the joint geometry on the strength and stiffness properties was investigated. Besides the optimal geometrical configurations of the dovetail joint, also a significant increase of the strength and stiffness properties with increasing connection length was identified.

Optimal design of mass timber panels as dynamic insulation: simulations of steady and transient heat exchange

Mass timber panels could be designed as heat exchangers for use in building envelopes. Fresh air, drawn through geometrically optimized channels in the panel, is pre-tempered with building heat that would otherwise be lost to the exterior via conduction. Recent experiments have shown that timber heat exchanging panels can approach U ~0.1 W/m2K – but there are potential limitations. The sizing correlations which predict panel geometry and steady heat exchange must be numerically calibrated for building-scale contexts, the heat-exchange efficiency must be verified virtually, and practical thresholds for transient response time must be determined. This study uses numerical simulations to investigate these factors for one design ‘case’ of timber panels, and establishes a methodology for studies of further cases.

Preliminary investigation on the transient hygrothermal analysis of a CLT-based retrofit solution for exterior walls

This paper investigates the transient hygrothermal performance of an innovative energy and seismic renovation solution for reinforced concrete (RC) framed buildings, based on the addition of Cross-Laminated Timber (CLT) panels to the outer walls, in combination with wood-based insulation. This solution is being developed in the framework of a four-year EU-funded project called e-SAFE. The investigation relies on numerical simulations in DELPHIN 6.1, by considering combined heat and mass transfer (HAMT) due to water vapour diffusion and capillary transport. The proposed solution is tested in three different climates in Italy, to verify whether the CLT layer and the outer waterproof vapour-open membrane, inserted to protect the wood-based insulation from rain, still allow the effective drying of the vapour accumulated in liquid form in the walls, while also preventing mould formation. The results show that the increased thermal resistance of the wall assembly significantly reduces the total water content, although moderate risks of mould growth in the wooden materials may occur in coldest climates.

Experimental Study on Torsional Behavior of Cross-Laminated Timber Skewed Pedestrian Bridge Deck Panels Subjected to Asymmetric Loading

AbstractThe performance of cross-laminated timber (CLT) panels in building applications have been investigated extensively. However, limited information is available regarding the performance of CL...

Modeling of Cross-Laminated Timber (CLT) panels loaded with combined out-of-plane bending and compression

Rolling shear is one of the major concerns that significantly impact the performance of CLT walls if they are subjected to combined out-of-plane bending and compression loads. Because the effects of rolling shear and out-of-plane bending are coupled to each other, prediction of the load-carrying capacity of CLT wall is always a challenge for the design of CLT structures. Current design codes employ an Ayrton-Perry type interaction equation as the failure criterion to check the safety of a CLT panel loaded with combined bending and compression. Nevertheless, there is no model available to predict their load-carrying capacity. The presented work aims at developing an analytical model to predict the load-carrying capacity of CLT wall loaded with combined out-of-plane bending and compression. In total 12 five-layer CLT panels loaded with different initial load eccentricities were tested to investigate the failure modes. Observed during the test were two ultimate failure modes, i.e., compression crush on the concave side and tension rupture in convex side. Based on these failure modes and deeming the test member as a beam-column, an analytical model which takes rolling shear effects into account to predict the load-carry capacity of CLT compression-bending members was developed. An explicit formula based on compression failure mode was proposed. The model is capable of determining the distribution of rolling shear stress along longitudinal direction, rolling shear-induced axial force and moments in CLT beam-columns. By calculating the load-carrying capacities of the specimens tested in this study as well as the additional three- and seven-layer specimens tested by another studies, it was found that the compression failure mode-based formula can provide good agreements with the test results.

Method of calculation of panel buildings from cross-laminated timber

Building constructions made of cross-laminated timber become more and more widespread. Experience in the timber structures design and operation for various purposes confirms the feasibility of their use. Recently, the construction of prefabricated cross-laminated timber houses has become especially widespread. The problem solution of cross-laminated timber panels calculation by means of a finite element method with the material`s reduced mechanical characteristics application is offered in this article. The specified formulas for definition of the reduced geometrical and mechanical characteristics of cross-laminated timber panels` various types, including those made of combined cross-laminated timber, are resulted. The algorithm of cross-laminated timber panels calculation by means of a finite element method is resulted. The possibility of using flat finite elements taking into account orthotropic properties for the calculation of cross-laminated timber panels using the elasticity above modulus according to the above method, adjusting the Poisson's ratios so as to preserve the condition of elastic potential in timber, is reasoned.

An Integrated Approach to Improve Seismic and Energetic Behaviour of RC Framed Buildings Using Timber Panels

In the present paper, an integrated intervention system applicable to concrete-framed buildings is presented. The purpose of the intervention is to improve both the seismic and the energetic behaviour of such buildings using cross-laminated timber (CLT) panels. Two alternative intervention configurations with different levels of invasiveness are described. Considering a double-wythe masonry-infilled frame, the most invasive configuration consists in the replacement of the external masonry wythe with the CLT panel, while the least invasive configuration consists in the arrangement of the CLT panel from the outside without removing the wythes. The technical details and implementation procedures were studied, considering functionality and disturbance to occupants. An isolated one-storey-one-bay frame was used as a reference for the seismic and thermal analyses. Subsequently, the two intervention configurations were applied to a case-study building by identifying two alternative intervention strategies. The obtained results showed that the proposed integrated intervention approach can significantly reduce both the seismic vulnerability and the energy consumption of concrete buildings.

Integrated Deep Renovation of Existing Buildings with Prefabricated Shell Exoskeleton

The European goal to reach carbon neutrality in 2050 has further put the focus on the construction sector, which is responsible for great impacts on the environment, and new sustainable solutions to renovate the existing building stock are currently under development. In this paper, the AdESA (Adeguamento Energetico Sismico ed Architettonico, in Italian) system, a holistic retrofit technique for the integrated renovation of the existing buildings, is presented. The system was developed by a consortium of enterprises and universities and was applied to a pilot building. The system consists of a dry, modular and flexible shell exoskeleton technique that implements different layers depending on the building retrofit needs (cross-laminated timber (CLT) panels for the structural retrofit, thermal insulation panels for the energy efficiency amelioration, and claddings for the architectural restyling). In order to foster actual sustainability, the solution contextually targets eco-efficiency, safety and resilience. To this end, the system not only couples the structural and energy interventions to reduce the operating costs, but it is also conceived in compliance with life cycle thinking (LCT) principles to reduce impacts throughout the remaining building service life (from retrofit time to the end of its life). The system is designed to be easily mountable and demountable to allow for the reuse/recycling of its components at the end of life by adopting macro-prefabricated dry components and standardized connections, to reduce damage caused by earthquakes by reducing the allowed inter-story drift, and by amassing the possible damage into sacrificial replaceable elements. The paper describes the AdESA system from a multidisciplinary perspective and its effective application for the deep renovation of an existing gymnasium hall.

Experimental and theoretical investigation of long-term performance of steel-timber composite beams

The structural performance of the steel-timber composite floors under sustained long-term loads was investigated by laboratory tests over a period of 22 months. The long-term deflections, end-slips, and strain distributions over the cross-section were measured and reported for six beams with a loading span of 5.8 m. Effects of different shear connectors, arrangement of the timber panels and timber slab segmentations and the magnitude of applied loads were studied. The timber slab segmentation had a detrimental effect on the short- and long-term stiffness of the tested beams. The long-term effects (after 22 months) led to a maximum 19% increase in the midspan deflections. Furthermore, the moisture transport, variation of mechanical properties with respect to moisture content, long-term compressive deformation of the panels and long-term slip moduli of the shear connectors were investigated to provide a thorough understating of the long-term behaviour of the steel-timber composite system. A simplified analytical model for estimating the flexural stiffness of the steel-timber composite beams was proposed and employed to estimate an overall creep deformation factor for the composite beams. The creep deformation factor of the tested beams was in the range of 0.29–0.39 depending on the shear connector type and timber slab orientation.

Experimental Investigation on Axial Compression of Resilient Nail-Cross-Laminated Timber Panels

Conventional cross-laminated timber is an engineered wood product consisting of solid-sawn lumber panels glued together. In this study, the structural behavior of solid wood panels of Nail-Cross-Laminated Timber (NCLT) panels connected with nails instead of glue was studied. The failure mode and nail deformation of the novel NCLT panels under axial compression load using eight full-scale NCLT panels was investigated. The effects of four key design parameters, namely, the nail type, number of nails, nail orientation angle, and nail slenderness ratio on axial compression performance of NCLT panels were also analyzed. In addition, a formula for predicting the axial compression bearing capacity of NCLT panels was developed. For calculation of the slenderness ratio, the moment of inertia of the full section or the effective section was determined based on the nail type, number of nails, angle of nail orientation and number of layers of the plate. Results showed that specimens connected by tapping screws had best compressive performance.

Diaphragm shear and diagonal compression testing of cross-laminated timber

To learn the characteristics of a cross-laminated timber (CLT) panel, it is crucial to perform experimental tests. This study presents two experimental test methods to measure the in-plane shear modulus of CLT panels. This characteristic can be measured by multiple methods such as the picture frame test, the diagonal compression test, and the diaphragm shear test. In this study, the same CLT panels are tested and evaluated in the diaphragm shear test and the diagonal compression test to see if more reliable results can be achieved from the diaphragm shear test. This evaluation is done by experimental tests and finite element simulations. The theoretical pure shear simulation is used as a reference case. Finite element simulations are made for both edge glued and non-edge glued CLT panels. Nine CLT panels are tested in the diaphragm shear test and the diagonal compression test. During ideal conditions (uniform material properties and contact conditions), all three simulated methods result in an almost equal shear modulus. During the experimental testing, the diagonal compression test gives more coherent results with the expected shear modulus based on finite element simulations. Based on the diaphragm shear test results, the CLT panels behave like edge glued, but this situation is dismissed. However, during ideal conditions, the diaphragm shear test is seen as a more reliable method due to the higher proportion of shear in the measured area.Article HighlightsComparing the two experimental methods: the diaphragm shear test and the diagonal compression test.Using the theoretical pure shear simulations to verify the experimental methods.Experimental testing and finite element analysis of the same cross-laminated timber panel.