Assessing the Fire Integrity Performance of Cross-Laminated Timber Floor Panel-to-Panel Joints

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.

Cross-laminated timber (CLT) is a product consisting of multiple timber layers (lamina) face-glued together to form structural wall and flooring systems. Internationally its use is growing rapidly, although its fire resistance is a topic of ongoing research. This study investigates the fire resistance of CLT wall panels manufactured locally from South African pine and eucalyptus, the most commonly used timber species for CLT in South Africa, through SANS10177-2 compliant fire tests of two 100 mm (33-33-33) thick CLT wall panel samples with dimensions of 0.9 m x 0.9 m. In addition to insulation and integrity fire resistance ratings, the study characterises the charring rate and delamination behaviour of CLT. The recommended integrity and insulation fire resistance ratings for the 100 mm thick SA pine and eucalyptus CLT samples is 60 minutes and 90 minutes respectively. The average charring rate calculated for the SA pine CLT and eucalyptus CLT panels was 0.95 mm/min and 0.76 mm/min respectively. These values are higher than charring rates for bulk timber, due to significant delamination observed in both tests. Associated structural fire resistance rating was estimated for each CLT panel by rational design, giving structural resistance times of 29 mins and 36 mins for the SA pine and eucalyptus CLT, respectively. These times are notably smaller than the insulation and integrity fire ratings reported above, but are only relevant to load-bearing walls. As a result, the tested CLT panels can only be used in multi-storey timber buildings as non-loading bearing walls.

Hygrothermal performance of cross-laminated timber wall assemblies with built-in moisture: field measurements and simulations

Wooden structures are increasingly being used in the construction of residential buildings. A common and often published reason to avoid wooden structures is their insufficient fire resistance, which reduces bearing capacity. For this reason, composite sandwich structures began to be designed to eliminate this drawback, as well as others. Recently, however, the trend is for a return to the original, wood-only variant and a search is underway for new technical means of improving the properties of such structures. Many timber structure technologies are known, but structures made from cross-laminated timber (CLT) panels have been used very often in recent years. CLT panels, also known as X-LAM, are currently gaining popularity in Europe. In the case of CLT panels composed of several layers of boards, they can be said to offer a certain advantage in that after the surface layer of a board has burnt and the subsurface layer has dried, oxygen is not drawn to the unburned wood for further combustion and thus the burning process ceases. CLT panels do not need to be specially modified or coated with fire resistant materials, although they are usually lined with gypsum-fibre fire resistant boards due to guidelines set out in the relevant standards. This paper presents a new method for the assessment of load-bearing perimeter walls fabricated from CLT panels without the use of an inner fire-retardant lining to ensure fire resistance at the level required by European standards (i.e. those harmonized for the Czech construction industry). The calculations were verified through laboratory tests which show that better parameters can be achieved during the classification of structures from the fire resistance point of view. The aim of the article is to utilize the results of assessment and testing by an accredited laboratory in order to demonstrate the possibilities of using CLT panels for the construction of multistorey as well as multi-purpose buildings in the Czech Republic.

Cross-laminated solid timber panels represent an interesting technical and economical product for modern timber structures. The use of large prefabricated cross-laminated solid timber panels for load-bearing wall and floor assemblies has become increasingly popular in particular for residential timber buildings. The fire behaviour of cross-laminated solid timber panels has been experimentally and numerically studied during two different ongoing research projects carried out at the Institute of Structural Engineering of ETH Zurich, Switzerland and the Trees and Timber Institute CNR-IVALSA in Trento, Italy. The paper presents the main results of the experimental and numerical analyses. Particular attention is given to the comparison of the fire behaviour of cross-laminated solid timber panels with homogeneous timber panels. The results of the analysis have shown that the fire behaviour of cross-laminated solid timber panels depends on the behaviour of the single layers. If the charred layers fall off, an increased charring rate needs to be taken into account. The same effect is observed for initially protected timber members after the fire protection has fallen off. Thus the fire behaviour of cross-laminated solid timber panels can be strongly influenced by the thickness and the number of layers. Further vertical structural members (walls) may show a better fire behaviour in comparison to horizontal members (slabs).

Airtightness of cross-laminated timber envelopes: Influence of moisture content, indoor humidity, orientation, and assembly

Wetting circumstances, expected moisture content, and drying performance of CLT end-grain edges based on field measurements and laboratory analysis

The Cross laminated timber (CLT) panels extended the market of timber material in structural construction, while its laminated structure allows layup design for utilizing low-value lumber. Through mechanical tests and numerical simulation, the mechanical properties of CLT made with low-value sugar maple (Acer saccharum) was first examined. The CLT panels made with white spruce (Picea glauca) salvaged from dead standing trees were examined. The mixed-species panels were prepared with the low-value sugar maple and salvaged spruce. The CLT panels were tested with the third-point and mid-point bending tests following ASTM D198 for major-axis flexural and shear properties. The CLT panels provided adequate flexural performance per current standard PRG 320-2019. The mechanical properties of the hybrid CLT panels with sugar maple surface layers were improved. In the meanwhile, the finite element model built with orthogonal constitutive law and progressive damage criteria simulated the mechanical behaviors of the tested CLT panels. Overall, the simulation results compared favorably with test data and provided reasonable estimates. A decomposed model with equivalent springs and shell elements based on the connection properties was developed to estimate the nonlinear dynamic performance of the conventional CLT shear wall. Full-size building simulation results indicated that the developed model could accurately estimate the wall dynamic performance. The dynamic performance of PT CLT rocking wall was also evaluated with numerical simulation. The similar equivalent decomposed wall model was developed and calibrated. A full-scale platform structure was simulated and compared with test results subjected to different seismic excitations. Because of the concentrated connection damage, the impact of sequential seismic-wind hazards on CLT shear wall systems is severer than that on traditional steel or reinforced concrete structures. With the developed conventional and PT wall models, the structural dynamic responses of different CLT wall systems were evaluated in wind-only and sequential seismic-wind scenarios. The wind-excited peak story displacement and acceleration for both CLT structures were magnified in the sequential seismic-wind scenarios compared with wind-only scenarios. The simulation results indicated that the sequential seismic-wind scenarios caused large acceleration with damaged connections for the conventional CLT shear wall structure. The PT CLT wall structure had minor displacement and acceleration, which was linear to the wind loading factors. The study of mechanical properties of the CLT panels made with low-value sugar maple and salvaged spruce can promote the utilization of the low-value lumber and promote forest management. The developed panel model provided an approach to estimate the

Numerical simulation of fire integrity resistance of full-scale gypsum-faced cross-laminated timber wall

Cross-laminated timber (CLT) is an innovative engineering wood product made by gluing layers of solid-sawn lumber at perpendicular angles. The commonly used wood species for CLT manufacturing include spruce-pine-fir (SPF), douglas fir-larch, and southern pine lumber. With the hope of broadening the wood species for CLT manufacturing, the purposes of this study include evaluating the mechanical properties of black spruce CLT and analyzing the influence of CLT thickness on its bending or shear properties. In this paper, bending, shear, and compressive tests were conducted respectively on 3-layer CLT panels with a thickness of 105 mm and on 5-layer CLT panels with a thickness of 155 mm, both of which were fabricated with No. 2-grade Canadian black spruce. Their bending or shear resisting properties as well as the failure modes were analyzed. Furthermore, comparison of mechanical properties was conducted between the black spruce CLT panels and the CLT panels fabricated with some other common wood species. Finally, for both the CLT bending panels and the CLT shear panels, their numerical models were developed and calibrated with the experimental results. For the CLT bending panels, results show that increasing the CLT thickness whilst maintaining identical span-to-thickness ratios can even slightly reduce the characteristic bending strength of the black spruce CLT. For the CLT shear panels, results show that increasing the CLT thickness whilst maintaining identical span-to-thickness ratios has little enhancement on their characteristic shear strength. For the CLT bending panels, their effective bending stiffness based on the Shear Analogy theory can be used as a more accurate prediction on their experiment-based global bending stiffness. The model of the CLT bending specimens is capable of predicting their bending properties; whereas, the model of the CLT shear specimens would underestimate their ultimate shear resisting capacity due to the absence of the rolling shear mechanism in the model, although the elastic stiffness can be predicted accurately. Overall, it is attested that the black spruce CLT can provide ideal bending or shear properties, which can be comparable to those of the CLT fabricated with other commonly used wood species. Besides, further efforts should focus on developing a numerical model that can consider the influence of the rolling shear mechanism.

Fabrication and use of Cross Laminated Timber (CLT) using tropical woods is still limited at present. Therefore objective of the present study aims to determine the possibility of using CLT panels of 3 and 5 layers, fabricated with Tectona grandis and Gmelina arborea wood using adhesive of isocyanate polymer emulsion system catalyzed with polymeric isocyanate. Delamination, water absorption, density, flexure test, compression and glue-line shear were evaluated using ANSI/APA PRG320-2012 ASTM D198 and ASTM D4761 standard. The results showed that CLT panels of T. grandis presented higher values of density, less water absorption and lower delamination, with no evident differences between the CLT of 3 and 5 layers. The high density of T. grandis resulted in higher values of the mechanical properties. The flatwise and edgewise flexure tests in 5-layer CLT panels of both species presented higher values of bending stiffness compared to those of 3-layer CLT panels. Further the bending stress values in 3-layer CLT panels were higher than for 5-layer CLT panels. As for shear stress in bending flatwise, in both species, 3-layer CLT surpassed 5-layer CLT panels, but in the edgewise test no differences were observed. The MOE and Fc in the compression test were superior in relation to the edgewise test. MOE and Fc in compression flatwise in 3-layer CLT was greater than in 5-layer CLT in both species, but edgewise these values were higher in 5-layer CLT panels. The most common failures were stress and delamination in the flexure test, whereas in the compression test these were: shearing, splitting and crushing. In the glue-line shear test no differences were observed between CLT panels of 3 and 5 layers for both species.

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.

Mid-rise to tall timber buildings are internationally gaining popularity. Reaching heights greater than 5 to 6 storeys has been made possible by the availability of engineered wood products, such as Laminated Veneer Lumber (LVL), Glued laminated timber (Glulam) and Cross Laminated Timber (CLT). These buildings are referred to as “mass timber buildings”. As the height of timber buildings increases, so do their potential risks of progressive collapse. Progressive collapse is characterised by a local failure of a load-bearing structural element which may propagate through the whole building, and ultimately causes its partial or entire collapse. While progressive collapse mechanisms of reinforced concrete and steel buildings have been widely researched, limited studies have been carried out on mass timber buildings. Their ability to resist progressive collapse and their load transfer mechanisms after the loss of a load-bearing element are currently unclear. First, to gain an initial understanding of the progressive collapse behaviour of post-and-beam mass timber buildings, a series of scaled-down 1×2-bay (2D) timber frame substructures were tested under a middle column removal scenario. The behaviour of the frames and the ability of three types of commercially used beam-to-column connections and a proposed novel connection, to develop catenary action under large deformations was measured. The system capacity in terms of the Uniformly Distributed Pressure (UDP) was also quantified. The test results showed that only the proposed novel connector was able to sustain the design pressure in international design specifications if no dynamic increase factor was considered, and therefore presented a potential solution to improve the robustness of post-and-beam mass timber buildings. Furthermore, progressive collapse of post-and-beam mass timber buildings cannot be resisted by the frame alone using the investigated currently used connections and alternative load paths must be found. Second to further explore the mechanisms of post-and-beam mass timber buildings against progressive collapse, four scaled-down 2×2-bay (3D) substructures, with CLT panels, were constructed and tested in the laboratory. Three substructures were tested under an edge column removal scenario, with substructures manufactured from two different types of beam-to-column connections. Namely, two tests were performed with a connection type commonly used in Australia, and one test with the proposed novel connection investigated earlier. The last substructure was subjected to two different corner column removal scenarios, with the substructure tested twice under different CLT panels configurations. The substructure was assembled from the commonly used in Australia beam-to-column connection. In all tests, two Uniformly Distributed Pressures (UDP) were applied to the floors in two stages: (i) a constant UDP of 4.8 kPa was first applied to the bays not adjacent to the removed column and (ii) an idealised UDP was then increasingly applied to the remaining bay(s) through a hydraulic jack connected to a six-point loading tree. The load redistribution mechanisms (alternative load paths), the structural response and failure modes were recorded. In general, experimental test results showed that the applied load was principally transferred to the three columns the closest to the removed column and that the CLT panels spanning over two bays were efficient in resisting the load. The layout of the CLT panels plays a critical role in resisting progressive collapse. A simplified analytical model, consistent with the current industry design practice and pre-defined alternative load paths, was used to predict the ultimate resistance capacity of the tested specimens and compared to the experimental capacities. Overall, the simplified methodology was found to be conservative. Third, finite element (FE) models were developed using the component model and validated against the 2D and 3D experimental results. The properties of the springs to be used in the component model were obtained from additional experimental component tests. CLT panels were simulated using layered shell elements while beam elements were used for the beams and columns. In the 2D numerical model, the ultimate load was accurately predicted and the development of compressive arch and catenary actions were well reproduced. The validated 2D model was then used to build the 3D model. For all tests, the 3D numerical models accurately predicted the overall load-displacement responses, load redistribution mechanisms, failure modes and strain developments in the beams and CLT panels. The validated numerical models were used to conduct a series of parametric studies to further examine the structural responses of the post-and-beam mass timber buildings. The results indicated that the structural capacity would be reduced when only using onebay long CLT panels, compared to using either staggered or all two-bay long CLT panels. Also, beam-to-column connections of the frames connected to the removed column could locally support the CLT panels above, providing an additional alternative load path for the structure in the context of progressive collapse, which is normally neglected in industry design practice.

This paper presents and discusses the results of an attempt that was made to determine the Type X, 12.7 mm and 15.9-mm-thick, gypsum board fall-off in fire resistance tests of different orientations (horizontal and vertical assemblies) for 83 and 41 full-scale floor and wall test assemblies, respectively. These tests were conducted at the National Research Council of Canada in accordance with the CAN/ULC–S101 standard, which is similar in fire exposure to the ASTM E119 fire resistance standard for updating the fire resistance ratings in the listed wall and floor assemblies in Part 9, Appendix A, of the National Building Codes of Canada. The results of tests were further analyzed to investigate the gypsum board fall-off for wall and floor assemblies. Four different approaches were investigated using the floor assemblies' test results to identify board fall-off criterion. The proposed temperature criterion selected is based on the sudden temperature rise on the back side of the fire exposed gypsum board due to the board fall-off. The same criterion was also used in predicting the gypsum board fall-off in wall assemblies. A comparison of the gypsum board fall-off based on test observations and temperature measurements and temperature criteria for gypsum board fall-off for both vertical and horizontal applications are presented and discussed.

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