A study was conducted with the primary objective of examining the efficacy of a standard block shear test method to assess the bond quality of cross-laminated timber (CLT) products. The secondary objective was to examine the effect of pressure and adhesive type on the block shear properties of CLT panels. The wood material used for the CLT samples was Select grade nominal 25 x 152-mm (1 x 6-inch) Hem-Fir. Three adhesive types were evaluated under two test conditions: dry and vacuum-pressure-dry (VPD), the latter as described in CSA standard O112.10. Shear strength and wood failure were evaluated for each test condition.
Among the four properties evaluated (dry and VPD shear strength, and dry and VPD wood failure), only the VPD wood failure showed consistency in assessing the bond quality of the CLT panels in terms of the factors (pressure and adhesive type) evaluated. Adhesive type had a strong effect on VPD wood failure. The different performance levels of the three adhesives were useful in providing insights into how the VPD block shear wood failure test responds to significant changes in CLT manufacturing parameters. The pressure used in fabricating the CLT panels showed a strong effect on VPD wood failure as demonstrated for one of the adhesives. VPD wood failure decreased with decreasing pressure. Although dry shear wood failure was able to detect the effect of pressure, it failed to detect the effect of adhesive type on the bond quality of the CLT panels.
These results provide support as to the effectiveness of the VPD block shear wood failure test in assessing the bond quality of CLT panels. The VPD conditioning treatment was able to identify poor bondline manufacturing conditions by observed changes in the mode of failure, which is also considered an indication of wood-adhesive bond durability. These results corroborate those obtained from the delamination test conducted in a previous study (Casilla et al. 2011).
Along with the delamination test proposed in an earlier report, the VPD block shear wood failure can be used to assess the CLT bond quality. Although promising, more testing is needed to assess whether the VPD block shear wood failure can be used in lieu of the delamination test. The other properties studied (shear strength and dry wood failure), however, were not found to be useful in consistently assessing bond line manufacturing quality.
A study was conducted with the primary objective of gathering information for the development of a protocol for evaluating the surface quality of cross-laminated timber (CLT) products. The secondary objectives were to examine the effect of moisture content (MC) reduction on the development of surface checks and gaps, and find ways of minimizing the checking problems in CLT panels. The wood materials used for the CLT samples were rough-sawn Select grade Hem-Fir boards 25 x 152 mm (1 x 6 inches). Polyurethane was the adhesive used. The development of checks and gaps were evaluated after drying at two temperature levels at ambient relative humidity (RH).
The checks and gaps, as a result of drying to 6% to 10% MC from an initial MC of 13%, occurred randomly depending upon the characteristics of the wood and the manner in which the outer laminas were laid up in the panel. Suggestions are made for minimizing checking and gap problems in CLT panels. The checks and gaps close when the panels are exposed to higher humidity.
Guidelines were proposed for the development of a protocol for classifying CLT panels into appearance grades in terms of the severity of checks and gaps. The grades can be based on the estimated dimensions of the checks and gaps, their frequency, and the number of laminas in which they appear.
This chapter provides general information about the manufacturing of CLT that may be of interest to the design community. The information contained in this chapter may also provide guidance to CLT manufacturers in the development of their plant operating specification document. Typical steps of the manufacturing process of CLT are described, and key process variables affecting adhesive bond quality of CLT products are discussed. Proposed methods for evaluating panel quality are presented.
Cross-laminated timber (CLT) products are used as load-carrying slab and wall elements in structural systems, thus load duration and creep behaviour are critical characteristics that should be taken into account in design. Given the nature of CLT with orthogonal arrangement of layers and either mechanically fastened with nails or wood dowels, or bonded with structural adhesive, CLT is more prone to time-dependent deformations under load (creep) than other engineered wood products such as glued-laminated timber.
Time-dependent behaviour of structural wood products is accounted for in design standards by providing load duration factors to adjust specified strengths. Since the Canadian Standard on Engineering Design in Wood (CSA O86-09) does not deal with CLT, it does not provide load duration and service condition factors. Until this can be rectified, two options are proposed for adopters of CLT systems in Canada. These include not only load duration and service factors, but also an approach to accounting for creep in CLT structural elements. The proposed recommendations are in line with the specifications in CSA O86-09 and Canadian National Building Code.
Le présent chapitre fournit de l’information générale sur la fabrication du CLT qui peut être intéressante pour les concepteurs. Les renseignements contenus dans ce chapitre peuvent également servir de guide aux fabricants de CLT quant au développement de leur cahier de spécifications d'exploitation d'usine.
Ce chapitre aborde également les étapes spécifiques du processus de fabrication de CLT et les variables de processus clés qui ont une incidence sur la qualité d’adhésion des lamelles des produits de CLT. On y retrouve également les méthodes proposées pour évaluer la qualité des panneaux.
The objective of the project is to develop/improve practical, reliable and internationally recognized methods for assessing/pre-screening the long-term structural performance of engineered wood products used in residential and non-residential applications.
As 6-storey wood-frame, massive-timber and hybrid wood buildings are increasingly accepted by more jurisdictions across Canada, there is a need to develop reliable elevator shaft designs that meet the minimum structural, fire, and sound requirements in building codes. Elevator shaft walls constructed with wood-based materials have the advantages of material compatibility, use of sustainable materials, and ease of construction.
In this exploratory study, selected elevator shaft wall designs built with nail-laminated-timber (NLT) structural elements were tested to investigate their sound insulation performance because little is known about the sound insulation performance of such wall assemblies. The tests were carried out in an acoustic mock-up facility in accordance to standard requirements, and provide preliminary data on the sound insulation performance of elevator shaft walls built with NLT panels.
Four different elevator shaft walls built with NLT panels were tested and their measured apparent sound insulation class (ASTC) ratings ranged from 18 to 39 depending on their construction details. Some of the reasons that may have contributed to the ASTC ratings obtained for the elevator shaft walls described in this report as well as recommendations for future designs were provided.
It is recommended to continue improving the sound insulation of elevator shaft walls built with NLT panels to meet or exceed the minimum requirements in building codes.
Wood design standards in Canada and the United States provide design values for floor and roof diaphragms with sheathing thickness ranging from 9.5 mm (3/8 in) up to 18.5 mm (3/4 in), that are supported by joists spaced less than 610 mm (24 in) on centre. This range of sheathing thicknesses is adequate for housing and small buildings, but for large non-residential structures, diaphragms with thicker sheathing and wider joist spacing may be more appropriate.
This paper includes the findings of a study aimed at providing research information suitable for implementing design values for diaphragms with thick sheathing in the North American wood design standards. Results from quasi-static monotonic tests on fifteen full-scale 7.3 m (24 ft) long by 2.4 m (8 ft) wide diaphragms framed with 38x191 mm or 38x235 mm (nominal 2x8 and 2x10, respectively) solid sawn lumber or laminated strand lumber and sheathed with plywood or oriented strand board are discussed.
A numerical model was developed using the finite element method. The basic properties of the sheathing, framing members and nailed connections were implemented in the model to replicate the structural behaviour of the diaphragms with thick panels. The numerical model was successfully validated against the experimental data. The shear resistance values for the diaphragms with thick panels tested in this study were calculated. The model may be used to interpolate between various diaphragm configurations and calculate shear resistance values for other configurations of diaphragms with thick sheathing.
In the long run, it is hoped that the use of thicker sheathing will enable the use of structural systems that are cost effective for wider joist or beam spacing than systems made with dimension lumber and traditional sheathing thickness. The experimental data and the model developed in this project will be used to develop proposals for implementation of wood floor and roof diaphragms with thick panels in the Canadian and United States wood design standards.
The objectives of this project are to provide research information suitable for implementing design procedures for diaphragms with thick sheathing in the Canadian Standard for Engineering Design in Wood (CAN/CSA O86.1) and to make the information available to other markets by publishing the results and recommended procedures in a journal article.
This report describes work to provide research information suitable for implementing design procedures for diaphragms with thick sheathing in the Canadian Standard for Engineering Design in Wood (CAN/CSA O86.1) and to make the information available to other markets by publishing the results and recommended procedures in a journal article.