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.
Glulam rivets (or Griplam nails) are high strength steel nails originally developed in Canada to connect glued-laminated timbers (glulam) by means of pre-drilled steel side plates. Glulam rivets are considered one of the most efficient connectors in wood construction mainly because of their high load carrying capacity. However, CSA-O86.1, Code for Engineering Design in Wood does not provide design values for glulam rivet connections with sawn timber. The Fastenings Subcommittee of the CSA Technical Committee (TC) on Engineering Design in Wood has identified a need to extend the use of glulam rivet connections to sawn timber with appropriate service condition factors, and to investigate the effect of plate thickness on joint capacity. This project involving testing and analysis of sawn timber glulam rivet connections was initiated in the 1990/91 fiscal year. Since then, progress has been communicated to members of the Glulam Rivet Task Group of the TC on Engineering Design in Wood. Lateral resistance, rivet withdrawal, rivet embedment, and rivet bending tests were performed. Lateral load resistance test data were analyzed to investigate the effect of species, loading type and direction, environmental conditions, density, waiting period between assembly and test, pre-drilling, and plate thickness. Withdrawal load test data were analysed to investigate the effect of species, environmental conditions, density and waiting period. Recommendations for code implementation were made. Rivet embedment and rivet bending test data were used as input parameters with the European Yield Theory to predict the lateral resistance in rivet yielding failure mode.
To assure the appropriate use of wood in large residential and non-residential buildings, it is necessary to carry out a comprehensive study of the resistance provided by these wood structures to lateral loads due to wind and earthquakes. Given that this is a topic of international interest, and there is a strong movement towards worldwide harmonisation of codes and standards, the proposed work requires the cooperation of a number of specialists in Canada and abroad. As a first step in creating a coordinated program of research, a consultation on the seismic resistance of timber structures has been carried out. A group of six seismic experts from Japan, New Zealand, USA, Germany, Italy and Greece were brought together in Vancouver, B.C. for two days in May, 1993. This consultation was joined by six Canadian experts on seismic analysis and timber engineering research. Following this meeting, a five-year research program on the lateral resistance of engineered wood structures to seismic and wind loads was launched. The objective of the program is to provide designers and code writers with the test data and analytical tools needed to design large timber buildings for wind and earthquake forces. The program includes wood-framed and sheathed walls and diaphragms, braced timber structures, structural wood frames and arches. In the first year of the program, in cooperation with Dr. M. Yasumura, a visiting scientist from the Building Research Institute, Tsukuba, Japan, and Mr. D. Kishi, a structural engineering consultant from British Columbia, a total of 21 16' x 8' (4.8 m by 2.4 m) wood shear walls have been tested at Forintek under static and reversed cyclic loading. In these walls, three types of sheathing material (plywood, Oriented Strand Board, and Gypsum Wall Board (GWB) were used to investigate the effects of sheathing position (vertical or horizontal), blocking, nail spacing, and taping (in the case of GWB). The structural behaviour of elements such as shear walls is dependent on the behaviour of individual connections. Research alliances are currently being formed with the University of New Brunswick and the University of British Columbia for the development of test data and analytical models on the behaviour of connections.
Tree and log characteristics, wood properties, visually graded lumber yields, and machine-stress-rated (MSR) lumber yields were determined for 95 year-old lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) trees on good sites. A total of 220 trees were selected systematically by diameter-at-breast height (d.b.h.). Based on measurements of stand density made for plots around each sample tree, three samples were obtained which represented end-of-rotation stand densities of 700, 1100 and 1900 live stems/hectare (s/ha). Logs were sawn to maximize the yield of wide dimension lumber. Lumber recovery factor increased with increasing tree d.b.h. class, but due to greater stem taper, it was generally lowest for a given d.b.h. class in the 700 s/ha stand density class. Due to decreasing knot size, yields of Select Structural lumber increased as stand density increased (45.6, 62.5 and 65.4% for the 700, 1100 and 1900 s/ha samples respectively) but knots were small enough that a high proportion of lumber (greater than 90%) was visually graded No.2 & Btr. in all three stand density classes. Wood basic relative density was significantly inversely related to d.b.h., but was not significantly related to crown persistence or stand density. Lumber modulus-of-rupture (MOR) and modulus-of-elasticity (MOE) decreased as tree d.b.h. increased. Wide dimension lumber from open-grown trees generally failed to meet in-grade specifications for MOR and MOE. Lower MOR and MOE values were reflected in reductions in MSR yields. The juvenile wood proportion of tree stems, defined either as 15 or 30 annual rings from the pith, was only weakly related to lumber MOR and MOE. Kiln drying degrade increased with stand density class and ranged from 3% of pieces in the 700 s/ha sample to 7% of pieces in the 1900 s/ha sample. Drying degrade was essentially unrelated to proportions of juvenile wood. Application of study results to theoretical tree size and volume distributions generated by a stand growth and yield model (TASS) produced stand yields which in terms of lumber recovery, and premium structural and appearance grades, would rank stand densities in the following descending order: 1100, 700 and 1900 s/ha. Study results indicate that, for lodgepole pine grown on good sites, stand managers will achieve the optimal combination of lumber yield and grade by targeting a medium final stand density. Further research is underway to determine if the inverse relationship between average basic wood density and large diameter trees recorded in this regional study persists in other biogeoclimatic zones. It is important to note that, because of the systematic method of selecting trees by d.b.h. and stand density classes, the lumber strength and stiffness results obtained in this study are not representative of the current lodgepole pine resource in general.
The current American standard requires a minimum incision density for western white spruce and Engelmann spruce, but not for any other species. This requirement was based on the available data on the treatability of the western spruces with chromated copper arsenate. This preservative does not penetrate spruce as well as the ammoniacal preservatives. It therefore seemed likely that high-density incising may not be required when using the ammoniacal preservatives. End-matched samples of spruce from six sawmills were single-density- or double-density-incised and commercially treated with one of two preservatives, Ammoniacal Copper Quat (ACQ) or Ammoniacal Copper Citrate (ACcit). Both double-density and single-density-incised lumber from all six mills treated with both preservatives met the AWPA C2 standard. Conventional incision densities of around 6000 incisions per square meter were more than adequate to meet the standard.
Preparation of a didecyldimethylammonium chloride standard for the determination of DDAC content in commercial products|An investigation of the didecyldimethylammonium chloride content of sapstain control products
The didecyldimethylammonium chloride (DDAC) content of six Bardac 2280 samples (Lonza Inc.), the commercial DDAC concentrate, was determined and found to be variable. Because of the uncertain DDAC content of the Bardac used to calibrate the HPLC, solid DDAC was prepared and characterized using Pyrolysis/GC/MS, HPLC, carbon, hydrogen and nitrogen analysis and NMR spectroscopy. Bardac 2280 was analyzed using the solid DDAC calibration standard and found to contain 68 - 76% DDAC.
A questionnaire was mailed to B.C. sawmills producing hem-fir lumber to obtain information regarding hemlock brownstain. The incidence of hemlock brownstain was moderate in 1992. The survey showed that hemlock brownstain could occur at any time of year but spring and fall are more severe. Second growth as well as old growth is problematic and hemlock brownstain predominates in sapwood. An overview of general handling practices for western hemlock and amabilis fir logs prior to sawing of lumber was given. Factors affecting the development of hemlock brownstain were not clearly identified.
This report contains three draft papers concerning field test data. The first paper, "Modelling data from stake tests of wood preservatives," presents a simplified method for using such data. The second paper, "Using stake test data in wood preservation standards," provides a number of examples of how this method can be used to draw practical conclusions from such data. The third paper, "Performance of preservative-treated veneered composites: 1993 data," discusses the effect on performance of using preservatives in plywood and LVL rather than solid wood. Before any substantial change can be made to standards, data must be generated in support of such a change. In the case of wood preservatives the most important part of the data package is the performance in field tests. The standard method for interpreting stake test data is seldom used because it is somewhat unwieldy. What was needed was a simplified method which would be easily understandable by industry, academics and other standards committee members alike. Regression lines have been fitted to plots of decay rating against time for a range of preservative retentions. The slope of these lines was then plotted against retention using a log-log transformation. A rate of decay can then be determined for any given retention. This method has been used to compare the efficacy of different preservatives, compare the effect of wood species and evaluate the extension of service life resulting from increasing preservative retention. The model developed shows an excellent fit to the data from most of the waterborne preservatives in tests. Comparison between preservatives can be made on the basis of the retention required to give the same decay rate as 6.4 kg/m3 of CCA-C. For ACC this was 8.2 kg/m3, virtually identical to the retention specified for this preservative in the AWPA C2 standard. Increasing the retention of CCA from 6.4 to 9.6 kg/m3 increases the estimated stake service life (time to a rating of 70) by 54%. The effect of wood species can be assessed by determining the retention required to give the same decay rate as a standard retention in a standard wood species. For example, aspen was projected to require around 24 kg/m3 CCA to give the same decay rate as 6.4 kg/m3 in ponderosa pine. Using the methods developed here, retentions for new preservatives can now be suggested based on a practical comparison to already- standardised preservatives. There are indications that the higher retentions specified for PWF plywood and lumber will indeed provide the extended service life required of this system. Conventional stake tests use solid pine sapwood which treats through and through. In contrast, treatment of plywood commonly results in a patchy distribution of preservative. The influence of this preservative distribution on performance needed to be determined. The impact on performance of changing wood species and of field cut preservative application also needed to be addressed. Test stakes were cut from commercially treated plywood made from hem-fir and Pine-spruce. Some of this material was installed in a field test 14 years ago with and without field-cut preservative treatment on the edges. The hem-fir plywood was CCA- or ACA- treated. The pine-spruce plywood was CCA-treated. CCA- and ACA- treated aspen LVL was also put into test. Hem-fir plywood with the same preservative retention but a range of degrees of preservative penetration was installed in a soil-bed test. Despite small areas of untreated wood in the outer plys, hem-fir plywood has performed as well as solid wood treated to similar retentions over 14 years in test. Failure to apply field-cut preservative will substantially reduce the service life of preservative-treated plywood. Pine plywood with heartwood face veneers and field-cut treatment performed as well as hem-fir plywood. Plywood with sapwood face veneers did not perform as well. Variation in degree of preservative penetration has shown no effect on performance after 2.5 years in a soil-bed tests. Aspen LVL will require extremely high preservative loadings if it is to be used in exterior exposure. The data on plywood performance continues to support the recent modification to the CSA O80.15 standard to allow small areas of untreated wood in the outer plys. With further data, pine-spruce plywood might be considered for some applications where preservative treatment is required.
This report is a compilation of six draft papers. They describe laboratory and field work which has demonstrated that soil iron, mobilised under certain unusual conditions, can enter wood products in ground contact, detoxify the preservative and lead to premature decay. Forintek's field test site had been recognised as being highly aggressive towards copper and arsenic-based wood preservatives. Investigation of this phenomenon had revealed that iron was moving into wood from the soil. There were a number of ways in which this could contribute to accelerated decay and a program of research was designed to investigate this phenomenon. Premature failure of CCA- treated wood has been reported from a number of horticultural sites across the world. One such instance occurred in Penticton, B.C. and this was investigated to determine if soil iron might be involved. To eliminate the wide range of soil properties which could affect decay, much of the work has been done with iron, treated wood and brown-rot fungi under laboratory conditions using the soil-block test. Experiments have been designed to eliminate a number of possible effects of iron on the wood, the fungus and the preservative. Brown-rot fungi have then been used as a bioassay to determine which components of the preservative are affected by iron. One instance of premature failure of vineyard posts was investigated by a field survey, chemical analysis of samples and a laboratory experiment on the effect of organic soil amendment. Further soil properties affecting iron uptake have been investigated using small test stakes in containers of soil with a variety of amendments under a range of soil moisture conditions. Iron has been shown to increase the weight loss of CCA- and ACA- treated wood by a brown-rot fungus. It does not directly affect the fungus or the wood, nor does it cause leaching of the preservative. Iron does appear to detoxify the arsenic component of preservatives and may have an effect on copper at low copper and high iron loadings. Soil iron was implicated in the premature failure of vineyard posts. Iron uptake was promoted by continuously wet soil and organic amendments such as wood chips. Such conditions are typical of horticultural operations. These results suggest that North American wood preservation standards should have two levels of ground contact decay hazard as in the Australasian rather than the European system. When the use category system is implemented, horticultural posts should be treated to H5 rather than H4. Until then they should be regarded as "structural elements" and should be treated to the pole standard CSA O80.4 rather than the post standard CSA O80.5.
Borate treatment has the potential to provide termite resistance to Canadian lumber destined for use as sill plates in Japanese houses. Performance data is a prerequisite for approval of such a product by Japanese Codes and Standards authorities. Forintek therefore proposed a collaborative (University of Hawaii/University of Kyoto/Forintek Canada Corporation) field test of Canadian softwood lumber treated with borates. The first step in the procedure was to design and evaluate a suitable test method. With partial funding from the Japan Science and Technology Fund such a preliminary field test is now underway in Hawaii and Japan and is largely on schedule. However a one year delay in the Japanese portion of the test has resulted from the collaborator omitting to use bait stakes in the test termite bait stakes. Western hemlock sill plates (dodai) have been treated with both low and high levels of borate wood preservative, and, together with untreated wood, installed in a simulated sill plate field test at both sites. After five months, attack of untreated wood was demonstrated in the Japanese test in those replicates where termite bait stakes were used. In Hawaii, attack is prevalent on both controls and low-level-boron treated wood. Although not yet fully evaluated the test method appears to be successful. The main test is scheduled to begin later in 1994.
The recently revived interest in borate treatment for the production of termite-resistant lumber has led to the need for more rapid treatment processes. Pre-steaming prior to pressure treatment was known to have a number of potential benefits in terms of improved permeability, moisture distribution and vacuum. This process was therefore tried on western hemlock and amabilis fir Dodai (baby squares) in an attempt to achieve through-treatment without a diffusion period after pressure treatment. Western hemlock pre-steamed to a core temperature of 65 degrees C received a 25% increase in solution uptake and a 41% increase in mean heartwood penetration using a two hour pressure period. Amabilis fir pre-steamed to a core temperature of 90 degrees C received a 40% increase in solution uptake but no measurable increase in heartwood penetration. This was because penetration measured from the heartwood face was virtually complete in the amabilis fir treated without pre-steaming. Pre-steaming hemlock and amabilis fir Dodai appears to be a very effective means of improving uptake during pressure treatment. Further optimisation of this process is still possible.
The performance of decking with relatively shallow preservative penetration is currently of interest to standards committees. Fortunately, a variety of non-incised nominal 2 x 4 inch decking was put into test by Forintek's Vancouver laboratory between 1981 and 1985. Two sets of non-incised CCA-treated hem-fir with preservative penetrations close to the new CSA O80 decking standards have remained sound after 10 and 13 years exposure. Material which did not come close to this standard, in terms of penetration or retention, showed early signs of decay. Decking double-vacuum treated with 0.5% PCP, performed better than material dip treated with 5% PCP after 13 years in test. Decking treated with Arquad B-100 at 6.4 kg/m3, by uptake, has performed as well as decking CCA-treated to the new CSA O80 decking standard after nine years. Untreated lodgepole pine has performed better than untreated hem fir after 12 years exposure.
Two tests of field-cut preservatives were set up at the request of the Canadian Standards Association Technical Committee on Wood Preservation. Short lengths were cut from permanent wood foundation grade lumber, hem-fir in the west and jack pine in the east. The cut ends were coated with a range of field-cut preservatives. The samples were then laid horizontally, half buried in soil, at separate western and eastern test sites. Not all preservatives were tested at both sites. After six years exposure, chromated copper arsenate (CCA) was the only preservative performing well on both wood species.
The objective is to develop an economically, technically and environmentally viable process which will provide long-term protection against wood weathering without masking the natural colour and texture of wood. Progress is described.
