A major constraint to the Canadian wood preservation industry in both domestic and export markets is the difficulty of penetrating Canadian wood species with preservatives. FPInnovations has put considerable effort into various forms of improved mechanical incising but these have not been adopted by the industry due to adverse effects on throughput and appearance of the final product. Recently, work in Europe has shown promising results from biological incising using white-rot fungi that colonize wood relatively rapidly but decay slowly. The use of European isolates of fungi in North America may be constrained by phytosanitary concerns. This report covers an experiment to screen North American isolates of white-rot fungi for potential as biological control agents. A modification of the soil-block test method was used to evaluate the ability of a range of fungi to improve permeability without affecting strength properties. Wood samples were exposed to the fungi for zero, two, four and six week time increments and were then treated with a 1.5% ACQ-D solution. Preservative uptake was calculated based on change in weight before and after treatment. Two isolates of Dichomitus squalens were found that dramatically increased preservative uptake. These samples were tested for strength loss and preservative penetration. Spruce samples exposed to D. squalens isolate 78A for six weeks were completely penetrated with preservative (19 mm depth) in all six samples. D. squalens 78B also showed promising results in pine and spruce samples based on uptake and penetration data. No stiffness loss was detected in any of these samples based on results from the crushing tests.
The latest developments in seismic design philosophy have been geared towards developing of so called "resilient" or "low damage" innovative structural systems that can reduce damage to the structure while offering the same or higher levels of safety to occupants. One such innovative structural system is the Pres-Lam system that is a wood-hybrid system that utilizes post-tensioned (PT) mass timber components in both rigid-frame and wall-based buildings along with various types of energy disspators. To help implement the Pres-Lam system in Canada and the US, information about the system performance made with North American engineered wood products is needed. That information can later be used to develop design guidelines for the designers for wider acceptance of the system by the design community. Several components influence the performance of the Pres-Lam systems: the load-deformation properties of the engineered wood products under compression, load-deformation and energy dissipation properties of the dissipators used, placement of the dissiaptors in the system, and the level of post-tensioning force. The influence of all these components on the performance of Pres-Lam wall systems under gravity and lateral loads was investigated in this research project. The research project consisted on two main parts: material tests and system tests.
In the material tests part of the program, a total of 110 compression tests were conducted to determine the load-deformation properties of four different engineered wood products (LVL, LSL, Glulam and CLT) in various directions. The LVL, LSL and Glulam specimens tested under compression parallel to grain had similar linear elastic behaviour with limited ductility. The CLT specimens tested under compression in the major-axis direction had linear elastic behaviour with moderate plasticity. Depending on the type of engineered wood product, typical failure modes included crushing, shear, wedge split and splitting. The compressive strength of the products tested ranged from 42.1 to 53.5 MPa, the global MOE (of the entire specimen under compression) varied between 6390 and 9554 MPa, the local (near the crushing surface) MOE parallel to grain was in the range of 2211 to 5090 MPa, while the local to global MOE ratio ranged from 29.2 to 58.0%, and was higher with the increase in the oven-dry density.
The specimens of the four different engineered wood products tested under compression perpendicular to grain or in the minor-axis direction had elastic-plastic behaviour with a clearly defined plastic plateau. Crushing (densification) of the fibres perpendicular to grain was the main failure mode for all specimens, and was in some cases followed by in-plane shear failure or cracking perpendicular to grain. Compression parallel to grain in the middle layer that was followed by its delamination and buckling was a unique failure mode for CLT specimens tested under compression in the minor strength direction. The compressive strength of the engineered wood products tested were in the range of 4.8 to 27.8 MPa, while the global and local MOE perpendicular to grain were in the range of 244 to 2555 MPa, and 320 to 1726 MPa, respectively. The compressive strength and global MOE perpendicular to grain increased with an increase in the oven-dry density. The results show no well-defined trend for the local MOE perpendicular to grain. The specimens loaded in the centre perpendicular to grain had higher strength, global and local MOE than those loaded at the end.
A convenient and timesaving design for the axial energy dissipators (fuses) was developed by replacing the epoxy in the original design with two half-tubes. Compared to the original design of fuses with epoxy, the new design with two half-tubes had similar necking failure mode and a longer failure displacment, thus providing user-friendly fuses that performed similar or even better than the original design.
In the system tests part of the program, a total of 17 different PT and Pres-Lam CLT walls with six different configurations were tested under monotonic and reversed cyclic loading. The studied parameters included the level of PT force, the position of the fuses, and the number of UFPs. CLT shear walls subjected only to post-tensioning, had non-linear elastic behaviour. The behaviour of the PT walls with and without energy dissipators was relatively similar under monotonic and cyclic loading. The strength degradation observed during the cyclic tests was low in all wall configurations suggesting that very little damage was inflicted upon the structure during the first cycles at any deformation level. Four major failure modes, including yielding and buckling of fuse, crushing and splitting of wood at the end of wall, and buckling of lumber in the exterior-layer of CLT wall, were observed in the tests. The yielding in fuses occurred at the early stage of loading as designed and the other failure modes happened when the lateral drift reached or beyond 2.5%.
The initial stiffness of the single-panel PT CLT walls tested ranged from 1.80 to 2.31 kN/mm, the load at the decompression point and 2.5% drift were in the range of 4.2 to 14.9 kN and 32.7 to 45.9 kN, respectively. The initial stiffness of the single-panel Pres-Lam CLT walls tested ranged from 1.69 to 2.44 kN/mm, the load at the decompression point and 2.5% drift were in the range of 21.0 to 30.2 kN and 59.6 to 69.8 kN, respectively. All the mechanical properties increased with an increase in the PT force. The average initial stiffness and the load at 2.5% drift of the coupled-panel Pres-Lam CLT walls tested were 4.59 kN/mm and 151.3 kN, respectively, while the load at the decompression point increased from 58.4 to 69.7 kN by increasing the number of UFP. The test results show that the behaviour of the Pre-Lam CLT shear walls can be de-coupled and a “superposition rule” can be applied to obtain the stiffness and resistance of such system.
The test results gave a valuable insight into the structural behaviour of the PT and Pres-Lam CLT shear wall under in-plane lateral loads. The data from the testing will be used in the future for development of numerical computer models. They will also be used for development of design guidelines for this system. All tests conducted in this study and the analyses in the future modelling research will form the basis for developing future design guidelines for PT and Pres-Lam mass timber systems.
The main project objective is to identify the wood-rotting fungi causing decay in Canadian buildings, and to provide data for a numerical model which will provide an indication of the time required for initiation of strength loss in wood-based panels when exposed to a range of moisture contents and temperatures. The project is divided into two phases; the pilot study reported here is the first phase of the project. The objective of this phase of the work was to develop an appropriate test method.
The Moisture Management in Exterior Wall Systems consortium led by the National Research Council’s Institute for Research in Construction is developing a computer model to predict the moisture and temperature conditions within a construction assembly in service. By including a damage function calculation for the various building components, the model can predict the consequences of these conditions in terms of strength loss.
Forintek’s role is to develop an experimental protocol that will be universally acceptable in the field of wood science, and generate a data set from which to derive a damage equation for wood decay as a function of time, temperature and moisture conditions. Discussions have established that strength loss in sheathing is the first priority.
A series of proposed test methods were examined. In consultation with members of the consortium task force, a method was developed which was anticipated to provide suitable strength loss data within the constraints of the funding available. The proposed method will subject sheathing samples to various combinations of temperature and humidity and to repeated inoculations with small amounts of a wood-rotting fungus to simulate natural infection. The samples will be monitored first using non-destructive testing and then destructively tested when a change in strength properties is detected. The result is a two-stage test at a range of temperatures and humidity levels, giving a measurement of time to strength loss.
This report is the final one on a pilot study to develop, refine and verify the proposed test method. "Method B" of ASTM 3043 (ASTM, 1999) was evaluated to determine if it was appropriate. The test monitored the bending stiffness and bending failure strength of oriented strand board samples, using a 4-point flexure test. The pilot study exposed samples to 20°C and 99.9% relative humidity and monitored bending stiffness loss as a proxy for bending failure strength loss. When there appeared to be a loss in bending stiffness, samples were destructively tested for bending failure strength loss.
Under the pilot test conditions, samples reached equilibrium moisture content within one month and were rapidly infected with xerophilic moulds. These died off within three to four months to be replaced by an unknown basidiomycete, first noticed after about 11 months. Bending strength loss occurred slowly and was first evident at approximately eight months. Presumably the basidiomycete had been active at this stage, but growth had not progressed to the stage of being noticeable to the naked eye. Only minimal strength loss had occurred after one year in test. Unfortunately, an electrical fault outside the safety cutoff caused the conditioning chamber to overheat after 15.5 months, killing the fungi growing on the samples and thereby terminating the test.
Based on results in the pilot study, recommendations have been made concerning moisture control and general operation of the environmental chambers. Recommendations have also been made regarding the disposition of samples in future tests, the time required for conditioning prior to inoculation and the actual bending stiffness and bending failure strength test procedures. The inoculation protocol should be continued but provision should also be made for more uniform natural infection of the test specimens.
A group of 2x4 SPF samples was tested for bending stiffness in the Western laboratory of Forintek and then re-tested in the Eastern laboratory . Another group of 2x4 SPF samples was tested for bending stiffness in the Eastern laboratory and then re-tested in the Western laboratory. The bending stiffness tests were conducted on test machines set up in accordance with ASTM Standard D198-02. Additional bending tests were done according to ASTM D4761-02A using the “portable bending” machine in the Western laboratory and a modified Metriguard 312 bending machine in the Eastern laboratory.
Results from ASTM D198-02 bending stiffness tests showed a differences between the laboratories of 2.1% for the sample originating from the Western Laboratory and 1.5% for the sample originating from the Eastern Laboratory. The MOE bending test results were not adjusted to account for any increase or decrease in the moisture content of the specimens.
Braced mass timber (MT) frames are one of the most efficient structural systems to resist lateral loads induced by earthquakes or high winds. Although braced frames are presented as a system in the National Building Code of Canada (NBCC), no design guidelines currently exist in CSA O86. That not only leaves these efficient systems out of reach of designers, but also puts them in danger of being eliminated from NBCC. The main objective of this project was to develop the technical information needed for development of design guidelines for braced MT frames as a lateral load resisting system in CSA O86.
In the first year of the project, the seismic performance of thirty (30) braced MT frames with riveted connections with various numbers of storeys, storey heights, and bay aspect ratios were studied by conducting non-linear pushover and dynamic time-history analyses. Also, fifteen (15) glulam brace specimens using bolted connections with different slenderness ratios were tested under monotonic and cyclic loading. Results from this multi-year project will form the basis for developing comprehensive design guidelines for braced frames in CSA O86.
Results from the first two years of the research project on the performance of structural systems with glulam riveted connections in non-residential buildings are presented in this report. The emphasis is placed on use of glulam rivets in structural systems such as braced frames and moment resisting frames.
Initially a comprehensive literature survey on the topic is given, including the historical development of the fastener and previous research work. This is followed by state-of-the-art information on the static and dynamic behaviour of glulam riveted connections in heavy timber construction. Research results include information from the following phases of the project:
Bending and tension tests to determine the material properties of glulam rivets as fasteners;
Embedment tests of glulam rivets in various wood products parallel, perpendicular and oblique to grain or strand;
Quasi-static monotonic compression tests on small riveted connections in various wood product loaded parallel and perpendicular to grain or strand;
Quasi-static monotonic and cyclic tests on axially loaded members with riveted connections used in braced timber frames;
Progress on the development of an analytical model to predict the resistance of riveted connections subjected to eccentric loading.
The results of the study cover riveted connections used with four different engineered wood products: Glulam, Laminated Veneer Lumber (LVL), Parallel Strand Lumber (PSL), and Laminated Strand Lumber (LSL). It should be noted that a comparison of the behaviour of riveted connections in different wood-based products was not the objective of the study. Consequently, the material sampling plan included one manufacturer per product.
The study will help provide relevant information that will be used to produce technical guidelines for design and construction of both types of frames with riveted connections. Such design guidelines and performance characteristics currently exist for structural systems in other construction materials such as steel and concrete, while with exception of wood-frame shear walls, they are virtually nonexistent for other wood–based structural systems.
Results from a three-year research project on the performance of structural systems with glulam riveted connections in non-residential buildings are presented in this report. The emphasis is placed on use of timber rivets in structural systems such as braced frames and moment resisting frames.
Initially a comprehensive literature survey on the topic is given, including the historical development of the fastener and previous research work. This is followed by state-of-the-art information on the static and dynamic behaviour of glulam riveted connections in heavy timber construction. Research results include information on all phases of the project:
· Bending and tension tests to determine the material properties of timber rivets as fasteners;
· Embedment tests of timber rivets in various wood products parallel and perpendicular to grain or strand;
· Quasi-static monotonic compression tests on small riveted connections in four different wood products loaded parallel and perpendicular to grain or strand;
· Quasi-static monotonic and cyclic tests on axially loaded members with riveted connections used in braced timber frames;
· Cyclic tests on portal moment resistant frames with riveted connections in four different wood products;
· An analytical methodology to quantify the dynamic performance of braced frames with timber rivets;
· Force modification factors for braced timber frames with riveted connections according to the NBCC.
· Force modification factors for portal moment resisting frames with riveted connections according to the NBCC;
Results of the study cover riveted connections in four different engineered wood products: Glulam, Laminated Veneer Lumber (LVL), Parallel Strand Lumber (PSL), and Laminated Strand Lumber (LSL). It should be noted that a comparison of the behaviour of riveted connections in different wood-based products was not the objective of the study. Consequently, the material sampling plan included one manufacturer per product.
The study provides relevant information that may be used to produce technical guidelines for design and construction of both types of frames with riveted connections. Such design guidelines and performance characteristics currently exist for structural systems in other construction materials such as steel and concrete, while with exception of wood-frame shear walls, they are virtually nonexistent for other wood–based structural systems.