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.
The highlights of a co-operative research program developed by the U.S. Forest Products Laboratory (FPL) and Forintek Canada Corp. to provide detailed creep-rupture and some creep information for composite panel products are summarized here. Support for this program has been provided by the American Plywood Association, The Waferboard Association (now the Structural Board Association), as well as the U.S. and Canadian Forest Services. Commercially produced plywood, oriented strandboard (OSB), and waferboard were tested to identify three mills that produced panels with high, low and median flexural creep performance. These three plywood, three OSB, and three waferboard products were then extensively tested to provide information on their duration of load and creep performance.
The work presented in this report is a continuation of the FPInnovations' research project on determining the performance of the CLT as a structural system under lateral loads. As currently there are no standardized methods for determining the resistance of CLT shearwalls under lateral loads, the design approaches are left at discretion of the designers. The most common approach that is currently used in Europe and North America assumes that the resistance of CLT walls is a simple summary of the shear resistance of all connectors at the bottom of the wall. In this report some new analytical models for predicting of the design (factored) resistance of CLT walls under lateral loads were developed based on connection properties. These new models were than evaluated for their consistency along with the models that are currently used in North America and in Europe.
In total five different design models (approaches) were used in the study, the two existing models and three newly developed ones. All models were used to predict the factored lateral load resistances of various CLT wall configurations tested in 2010 at FPInnovations. The analyzed walls had different aspect ratios and segmentation, different vertical load levels, different connection layouts and different fasteners in the connections (ring nails, spiral nails and screws). The design values obtained using the various analytical models were compared with the maximum forces and yielding forces obtained from the experimental tests. Ratios between the ultimate loads obtained from experimental tests and design values obtained by the five analytical design models were used as a measure for the consistency of the models. Newly developed models that account for sliding-uplift interaction in the brackets (models D3-D5) showed higher level of consistency compared to existing ones. The analytical model D4 that accounts for sliding-uplift interaction according to a circular domain, is probably the best candidate for future development of design procedures for determining resistance of CLT walls under lateral loads. In case of coupled CLT walls, contribution of vertical load to the wall lateral resistance was found to be two times lower than in case of single wall element with the same geometry and vertical load. Special attention in the coupled walls design should be given to step joints between the adjacent wall panels. Over-design of the step joint can result in completely different wall behavior in terms of mechanical properties (strength, ductility, deformation capacity, etc.) that those predicted.
It should be noted that conclusions made in this report are made based on the comparison to the tested configurations only. Additional experimental data or results from numerical parametric analyses are needed to cover additional variations in wall parameters such as wall geometry and aspect ratio, layout of connectors (hold-downs, brackets), type and number of fasteners used in the connectors, and the amount of vertical load. The findings in this report, however, give a solid base for the development of seismic design procedure for CLT structures. Such procedure should also include capacity based design principles, which take into account statistical distributions of connections resistances.
This report summarizes the experimental works that was carried out for a one-year research project developed as the continuation of previous research projects on the subject of light weight hollow core sandwich panels. The experiment focused on the investigation of creep behavior of light weight hollow core panel under long term static loading and high humidity conditions and its correlation with short term properties. Five types of surface panels were used, namely, 3.2 mm thick high density fibreboard with birch veneer on both sides, two thicknesses of M2 grade particleboard (6.3 mm and 9.5 mm) and two thicknesses of medium density fibreboard (6.3 mm and 9.5 mm). All panels were fabricated to the same final sandwich thickness of 45 mm using cell size of 12.7 mm Kraft paper honeycomb.
The results of the experiment show that the strongest facing material used to make the sandwich panels was the 3.2 mm hardboard with wood veneer lamination on both sides running along the long axis of the panel and test specimen, followed by the 6.3 mm MDF and the 9.5 mm MDF. The experiment demonstrated that exposing the panels to high humidity could cause strength loss of up to half of the original strength. However, the result of the experiment also suggested that it would be difficult to accurately predict the long term creep behavior of the sandwich panels using their corresponding short term flexural properties as the correlation between creep deformation and flexural properties was rather weak under the testing procedure and condition used.
Technical information needed for the reliable and expanded structural use of commercial panel products alone or as components of composite structural elements have been identified. In addition, alternative models used for describing the creep and creep-rupture of wood and wood-based panels have been reviewed, and their advantages and limitations have been discussed. Finally both short and long term research needs have been considered, and possible action plans have been suggested.
This report presents the results of a pilot study of the equilibrium moisture content and tensile strength of 20.5 mm thick Canadian Softwood Plywood and 15.9 mm thick waferboard exposed to a range of climatic conditions. Plywood and waferboard were conditioned until they reached constant weight at 20 C/65%RH and 5 C/90%RH. In addition some of the plywood and waferboard test specimens conditioned at high humidity subsequently were moved to a 20 C/65%RH atmosphere where they remained until an equilibrium moisture content had been achieved. A fourth group of plywood and waferboard specimens were kept at ambient conditions in the laboratory. Additional groups of plywood specimens were conditioned at 20 C/50%RH, 20 C/80%RH and also reconditioned from wet to 20 C/50%RH. Density, moisture content and tensile strength of all specimens were determined after they had reached equilibrium moisture content. The results indicate that there can be large differences in the equilibrium moisture content of wood-based panel products. The results also indicate a strong moisture dependency for the tensile strength of waferboard. No clear trend for the tensile strength of plywood in relation to moisture content could be established by this study.
This final report summarises progress in the fourth and final year of this multi-year project intended to characterise the fire performance of decorative wood room-linings and finishes. Forintek is often asked when decorative wood panelling is permitted in our export markets as a wall lining, a ceiling lining and as wainscoting. The question is challenging because both building code requirements and fire test methods for room linings vary from country to country.
A literature review was undertaken that demonstrated that different countries apply different test methods to regulate the use of combustible interior finish. The single-burning item test is used in Europe and is likely to be adopted in China; the cone calorimeter test is used in Japan, Australia and New Zealand; and the Steiner tunnel test is used in North America. Since Canadian wood products are sold in a variety of markets, it was decided that Forintek should document how they perform in each of these tests.
As globalisation intensifies, there is much interest internationally in comparing the performance of products as assessed by the different test methods used in various jurisdictions in order to facilitate trade. The room-corner test is proving useful in this regard. Although expensive and time-consuming to run, of all the test methods used to quantify the performance of lining materials, it is most representative of real-world fire scenarios. Consequently the room-corner test has become a reference scenario whereby the results generated in other tests can be understood. In fact, as countries move towards harmonisation of standards, there is a tendency to base product acceptance on performance in either the national fire test method or in the ISO room-corner fire test.
An agreement was made with Southwest Research Institute (SwRI) to conduct tunnel tests (ASTM E84), cone calorimeter tests (ISO 5660 / ASTM E1354), single-burning-item tests (SBI / EN 13823) and room-corner tests (ISO 9705) on several wood products. The wood products were white pine boards, white oak boards, OSB, Douglas fir plywood and FRT Douglas fir plywood. Due to equipment problems, the final report was not forwarded to Forintek until March 27. This has left little opportunity for analysis of the results. However, Forintek scientists have reviewed some of the raw data and have concluded that, in the reference scenario, the room-corner test, wainscoting performs very well.
A detailed analysis of the test data generated for Forintek by SwRI will be undertaken and an amendment to this final report will be made by the end of the First Quarter in 2006-2007.
The results of this study will allow Forintek scientists to respond appropriately to questions from members about when decorative wood panelling is permitted in our export markets. Because the project has involved testing in the internationally sanctioned reference scenario, the room-corner test, the results of the study also allow Forintek to recommend where it may be possible to recommend relaxations in requirements for room lings and wainscoting in our international markets.