In order to provide bridge designers with better information, International Forest Products Limited (Interfor) asked the Forest Engineering Resarach Institute of Canada (FERIC) to evaluate the bending strength and stiffness of log stringers used for constructing bridges on forest roads in coastal British Columbia. Given the lack of definitive standards for testing this material, FERIC developed a field-based test procedure and designed a test facility for destructive testing of full-size, whole-log stringers obtained from second-growth stands. Sixteen coastal Douglas-fir and twelve western hemlock logs were tested in 2003. This report describes the test procedure and methods of analysis, presents the log bending strength and stiffness results, and makes recommendations regarding future testing.
The goal of this project, carried out at Forintek’s Quebec MDF Pilot Plant, was to develop an enhanced fibreboard product for exterior applications. The experimental work consisted of three different phases. Phase I consisted of selecting a suitable resin system from among five types of resin exposed to the same process conditions. Panels produced with the MUPF resin (resin R03) had the best overall moisture resistance and dimensional stability properties. Phase II defined optimal refining and hot pressing process conditions. Based on the experiment results and statistical analysis, a numerical optimization was carried out using Design Expert® computer software. Phase III examined the chemical modification of wood fibre by acetylation. The following conclusions can be reached from this research project:
Among the five different resin systems, resin R03 (an MUPF resin) produced the best overall panel properties for moisture resistance and dimensional stability and was most cost effective.
For resins R03 and R04 (MUF), post-press heat treatment showed marginal improvements in panel bonding strength, moisture resistance, and dimensional stability.
Panels made with MDI resin were comparable to R03 panels in terms of dry IB, but resulted in lower water resistance (lower one-hour boiling IB).
With resin R03, panel series S7 had the best overall panel properties among the 8 different types of panels made under the different process conditions.
Resin content of R03 in the panel had the greatest effect on IB, water resistance, and dimensional stability.
Higher steam temperature in the preheater improved panel moisture resistance and dimensional stability.
All properties tested in S7 produced results higher than those typical of wood plastic.
The cost to produce S7 is about 40% of the cost of wood plastic panels for similar applications.
Acetylated wood fibre demonstrated a great improvement in water resistance and dimensional stability. However, further research is required in order to find better adhesives and application methods to optimize MDF panel processes with acetylated fibre.
Wood fibre-based panel can replace wood plastic for exterior applications at a significant cost advantage.
Further work is required to optimize the process and to fully evaluate panel properties under long term outdoor conditions.
Western redcedar (WRC) is renowned for its high durability, which is due at least in part to the presence of extractives that are toxic to decay fungi. Western redcedar's naturally low equilibrium moisture content (EMC) may also be a protective factor, since fungi typically require 30% moisture content to grow. Extractives are thought to contribute to the low EMC by blocking water adsorption sites on the wood. The present work compared the EMC of extracted and un-extracted WRC heartwood and sapwood. Extracted WRC heartwood had higher EMC than un-extracted WRC heartwood in samples not affected by fungi, and WRC sapwood had higher EMC than adjacent heartwood. The presence of extractives was identified as being associated with the low EMC of WRC heartwood in these samples.
In this study, extensive veneer compression tests were conducted to examine the transverse compression behaviour of veneer at both ambient and controlled temperature and moisture content (MC) environments. Based on the results, a novel method was developed to characterize overall surface quality of veneer and other wood materials in terms of their bondability and compression behaviour.
The method would have significant implication in both theory and practice. In theory, the general wood compression theory would need to be modified. The revised wood compression theory would include four stages instead of commonly defined three. The first stage, which has long and so far been overlooked but is critically important, could be named as “non-linear conformation”. During this stage, the contact area increases nonlinearly with the load applied. It is this stage that directly reveals the interfacial bonding behaviour of wood materials such as veneer-to-veneer and strand-to-strand and their minimum compression required for achieving adequate contact (bonding). In practice, the method provides a fast and objective way of evaluating surface roughness/quality of veneer and other wood materials. The new method also establishes the maximum compression allowable for achieving the best panel performance in terms of bonding strength, stiffness and dimensional stability. Based on the concept of this method, it was further found that both minimum compression required and maximum compression allowable are independent of temperature and MC, which provides a direct benchmark to the material recovery during panel hot-pressing.
In a case study with Trembling aspen veneer, the variation of veneer surface roughness/quality and its effect on resulting material recovery were first revealed. Then, the optimum panel densification was identified for performance plywood and LVL products based on the frequency distribution of the minimum compression required and the maximum compression allowable. Finally, an overall veneer quality index was established to compare veneer overall quality for different species/thickness. The method shows good potential in practical applications for increased material recovery, reduced glue consumption and improved panel performance.
The seismic and wind design provisions for engineered wood structures in Canada have to be enhanced to be compatible with those already available for structures built according to other material standards. Such design provisions are of vital importance for ensuring the competitive position of timber structures relative to reinforced concrete and steel structures. This report provides information on the framework needed for development of such enhanced provisions for design of lateral load resisting systems in engineered wood buildings. Although the framework presented here is suggested for implementation in the Canadian wood design standard (CSAO86) in correlation with the National Building Code of Canada (NBCC - the Canadian model design code), the information provided can be used as a template for other national and international codes and standards.
In the beginning, a comprehensive review on the development of the seismic design procedures in Canada and the US is presented. This is followed by the information on seismic design principles and methods of seismic analysis throughout the world. In addition, a state-of-the-art survey is included on the development and current activities related to the performance based design procedures throughout the world. This is followed by the details that should form the new design section on lateral load resisting systems (LLRS) to be developed in CSAO86 during the next code cycle. It is suggested that in response to the changes already in place in the 2005 edition of the NBCC, besides systems such as shearwalls and diaphragms, the section should include subsections for braced frames and moment resisting frames. It is also suggested that a strong link should be made between the design section on connections and the new one on LLRS. Future editions of the CSAO86 should also be encouraged to use the reliability and performance based design provisions, as the codes in the area of seismic design worldwide are moving in that direction.
There are several ongoing research activities in the field of wood-based lateral load resisting systems and connections throughout Canada and the US. Cooperation between researchers, engineering community and regulatory representatives is vital for successful delivery of the design guidelines mentioned above.
The objectives of this project were to develop and validate a finite element (FE) model of the hygroscopic warping of OSB panels and to suggest panel structures that ensure a higher level of stability during the storage, handling and use of panels.
A modification of the methodology developed at Université Laval for solid wood and already applied to MDF panels at Forintek Canada Corp. was used for the determination of diffusion coefficients in OSB. An existing finite element model developed jointly by Forintek Canada Corp. and Université Laval for the evaluation of MDF warping was adapted to the characteristic OSB structure. The finite element model was based on an unsteady-state moisture transfer equation, a mechanical equilibrium equation, and an elastic constitutive law. The experimental inputs were the mechanical properties E1, E2, E3, G12, G13 and G23 all as a function of moisture content, density and strand orientation; the expansion properties b1, b2 and b3 as a function of density and alignment; sorption isotherms and diffusion coefficient generated by producing a total of 50 laboratory OSB panels: 18 one-layer panels without density profile and strands oriented through the entire thickness (6 x 500 kg/m³, 6 x 625 kg/m³, 6 x 800 kg/m³), 24 three-layer panels with density profile (16 panels with density 625 kg/m³, aligned strands in surface, random strands in core, and 8 panels with density 625 kg/m³, different alignment in the two surface layers, random strands in core) and 8 panels with density 625 kg/m³, random strands. The panels had dimensions after trimming of 838 mm x 838 mm x 10.5 mm (33 in x 33 in x 7/16 in). To validate the model, warp was initiated and its dynamics was monitored by submitting 2 panels from each group to an 80% relative humidity.
The results showed that for all one-side sealed panels, the MC-increase in the zones close to the surface at the early exposure stages caused rapidly a convex deformation towards the exposed surface. When MC gradually homogenized across thickness, most of the panels returned close to their original flat shape. For panels with a flat density profile, the higher the average panel density, the higher the level of warp due to the effect of density on the expansion and swelling properties. Panels with oriented strands experienced higher strain differential and therefore developed stronger warp compared to panels with random strands. Panels with a one-layer structure experienced higher warp compared to panels with a three-layer structure. When the sealed surface layer was thicker than the exposed surface layer, or when the alignment in the sealed layer was higher than the alignment of the exposed layer, the panels continued to distort and their warp became negative, instead of stabilizing close to their original flat form.
The agreement between the experimental results and the finite element results confirmed the validity of the proposed model in the conditions and the OSB properties considered in this work. Simulations with the finite element method were performed corresponding to specific industrial applications and allowed the creation of a large database of results, which served for building the software package WarpExpert.
In recent years, significant attention has been paid to the engineering performance of wood structural systems, and a new generation of more reliable engineered wood components for building construction has evolved.
The latest trend is towards advanced products that combine wood and synthetics. This increases performance and structural reliability of engineered wood products, and leads to new markets and expanded opportunities. It is anticipated that cost of fibre reinforcement decreases over time and advances developed on reinforcing techniques and methods of evaluation would provide wood producers with more options to better position their products in the marketplace.
A new reinforcing technique has been developed and applied to manufacture a hybrid wood product for structural applications. The technique involves a layering analogy using layers of synthetic reinforcement sandwiched between layers of wood composite. The products manufactured in the laboratory used regular OSB laminations and alternating layers of E-glass fabrics and resin. Three- and four-ply billets were manufactured with various layouts and then tests were conducted to characterize mechanical properties of the hybrid products. Overall, the test specimens performed well relative to the controls. Shear failures were observed as a result of the limited performance of OSB in shear, and consequently the next tests will be conducted with plywood laminations instead of OSB.
Selected issues related to code acceptance of structural FRP-reinforced wood products are discussed in the appendix. Future work is suggested to completely characterize and understand the properties and behaviour of the FRP-reinforced wood products, including fire performance, long term durability, maintenance and cost, in order to establish an environment in which to work comfortably with such materials. Overcoming these issues is vital for product acceptance in building codes.
FERIC has produced a guide for equipment operators, contractors and their field supervisors aimed at preventing soil damage from forest operations. A brief description of soils and soil damage categories is provided as are recommendations for choosing equipment options and operating techniques that reduce damaging soil disturbance.
This report summarizes the research project carried out at Forintek’s Eastern Laboratory entitled Properties of MDF in Relation to Wood fibre Characteristics and Processing. This project included two phases. In the first phase, 10 types of raw materials, including wood, bark, and tops, were selected to cover large range of wood characteristics. The samples were classified by wood species (e.g., the less desirable red pine species), fast growing and short rotation (e.g., hybrid poplar), residue type (e.g., tops and bark), and forest management regime (e.g., commercial thinnings). The basic properties of raw materials, such as basic density, pH, and buffering capacity, were determined. The effects of raw material acidity on the curing behaviours of UF resins were investigated, and the properties of MDF panels manufactured using each sample at fixed manufacturing conditions were compared. The impact of bark content on MDF properties was also studied. In the second phase, two types of raw materials (black spruce tops and bark) were selected for the optimization of process parameters, including refining and hot pressing. The effects of refining conditions on pH and buffering capacity of refined fibres as well as on the properties of MDF panels were investigated. Optimal refining and hot-pressing parameters were established for manufacturing MDF products with black spruce tops and bark. Based on the results of this study, the following conclusions can be made:
Buffering capacity and pH differ among species and type of raw materials. Bark has higher acid and alkaline buffering capacities and a lower pH value than wood of the same species due to their extractives. Ten-year-old poplar wood has a higher pH than six year old poplar wood, tops, and bark.
The pH value of the raw fibre materials studied decreases with increased absolute and relative acid buffering capacity due to the increased absolute acidity mass in the solution.
At lower levels of added catalyst, the effect of raw materials pH on UF resin gel time is significant, while it is insignificant at higher catalyst contents. This may be due to the acidity of wood, which is the main source of acid catalyst in mixtures with lower levels of added catalyst. In contrast, at higher levels of added catalyst, the catalyst is the main source of acid catalyst. With higher catalyst contents, all studied raw materials mixed with UF resin result in a longer gel time than with UF resin alone. The gel time of UF resin/wood mixture does not correlate to acid buffering capacity or alkaline buffering capacity, but there is a strong relationship between gel time and both absolute acid buffering capacity and relative acid buffering capacity.
The reaction enthalpy of UF resin increases with catalyst content. The activation energy and peak temperature of curing UF resin generally decrease with increased catalyst content at lower catalyst levels. However, with further increases in catalyst content, the changes in activation energy and peak temperature are insignificant. The hydrolysis reaction of cured UF resin occurs during the latter stages of the curing process at both lower-level (<0.2%) and higher-level (>0.7%) catalyst contents. This indicates that there is an optimal range of catalyst content for UF resin. The curing enthalpy of UF resin decreases with increased amounts of wood raw materials; this is due to the effect of diffusion induced by wood materials and the changes in the phase of curing systems. This suggests the curing reactions reach a lower final degree of conversion for wood/resin mixtures than for UF resin alone.
Hybrid poplar MDF panels show better mechanical properties than jack pine panels; the mechanical properties of jack pine panels are better to those of red pine and white spruce panels. The dimensional stability is the best in jack pine panels among the materials studied (poplar, red pine, and white spruce).
The effect of refining on wood pH is significant, but it is insignificant on bark pH. The pH values of the wood from all species studied reduced after refining.
The effect of bark on the modulus of rupture (MOR) and modulus of elasticity (MOE) of MDF panels is more significant than the effects on IB and other physical properties, such as thickness swelling (TS), water absorption (WA), and linear expansion (LE). All properties of MDF panels (except TS and, in one case, MOR) made with up to 40% bark meet the ANSI standard.
When black spruce tops are used as raw material for MDF, steam pressure is more important than retention time during the refining process in order to achieve better panel properties. The panels show very good mechanical properties and dimension stability under optimal refining conditions even without the addition of wax.
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.