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1.
Sandor Poncsak Duygu Kocaefe Ramdane Younsi Yasar Kocaefe Louis Gastonguay 《Wood Science and Technology》2009,43(5-6):471-486
Thermal treatment is used to preserve the wood without any addition of any toxic chemicals. This process increases the dimensional stability and darkens the color of the wood. The improvement of the resistance to decay of wood by thermal treatment is also often suggested in the literature. However, some latest works contested if the durability of heat-treated wood is improved when it is used in contact with ground. The objective of this study was to investigate the possibility of thermally treating electrical poles which are larger compared to the standard wood lumber. One of the applications for thermally treated wood poles could be their use in environmental sensitive areas (along rivers, for example) as a replacement for untreated western red cedar (WRC) poles which are more expensive. Green and pre-dried red pine (Pinus resinosa) and jack pine (Pinus banksiana) poles, both with circular and square cross-sections, were heated to high temperatures under humid and inert atmosphere. Operating parameters such as maximum treatment temperature, maintenance time at this temperature, heating rate and gas humidity were varied in order to find most suitable treatment conditions for the poles. The tests showed that most of the cracks are formed during the drying process while thermal treatment only widened already existing cracks. The circular shape seems to promote crack formation during the drying period since the directional dependence of shrinking creates more stresses in circular poles compared to the square poles. A slight decrease in flexibility of the wood with increasing temperatures was observed. The protecting effect of gas humidity against oxidation of wood and the importance of the application of a moderate heating rate for poles with large cross-sections are also demonstrated in this article. The impact of the heat treatment on the resistance to decay of electrical wood pole will be presented in a future publication. 相似文献
2.
Wallace E. Eslyn 《Wood Science and Technology》1970,4(2):97-103
Summary The Basidiomycetes associated with decay in pine, Douglas-fir, and cedar utility poles within various geographic regions of North America were investigated. On the basis of 313 isolations from these poles, 9 fungi appeared to be of major importance in internal pole decay in the United States. These fungi were the following: Lentinus lepideus, Lenzites saepiaria, L. trabea, Peniophora A., P. gigantea, and Poria radiculosa in pine, and L. lepideus, Poria carbonica, P. monticola, and P. xantha in Douglas-fir poles. Lentinus lepideus was overwhelmingly predominant in pine poles, whereas Poria carbonica was similarly predominant in Douglas-fir poles. Lenzites trabea was the fungus most often isolated from cedar poles; however, it is believed to be associated primarily with shell rot of cedar poles and to be of little significance, therefore, in causing internal decay of cedar. The fungi associated with western red-cedar and red and jack pine poles in Canada are listed, although the frequency of their occurrence is not included.This work was in cooperation with the Navy Department, Naval Facilities Engineering Command.The author is indebted to the following for furnishing cultures and pole sections or both for culturing or for information on the identities of the species of decay fungi found in Canadian poles: Joe Clark and John Kulp, U. S. Forest Products Laboratory, Madison, Wisconsin; Robert Graham and John Mothershead, Forest Research Laboratory, Oregon State University, Corvallis, Oregon; O. Floyd Hand, Bonneville Power Administration, Vancouver, Washington; John Shields, Canadian Forest Products Laboratory, Ottawa, Ontario; and John Roff, Canadian Forest Products Laboratory, Vancouver, British Columbia. The author is especially indebted to members of the Forest Disease Laboratory, Laurel, Maryland, for their invaluable aid in identifying representative cultures of many of the fungi discussed in this investigation.The Laboratory is maintained at Madison in cooperation with the University of Wisconsin. 相似文献
3.
Summary In part 1 of this series, a three-dimensional, structural analysis, finite element program has been developed to predict the stress distribution in wood poles with and without spiral grain and variable material properties. This program serves as a basis for a model to predict the strength and failure location in full-size wood poles. Fundamental to this model is the ability to quantify the effects of key material and geometric properties of the pole. This paper deals with the enhancement of the program to quantify the effect of knots and their associated cross grain on the stress distribution of wood poles. The technique is based on the theoretical behavior of laminar fluid flow around an elliptical obstruction. The flow-grain analogy was employed to develop empirical relationships between knot diameter and pertinent variables (grain deviation angle near the knot and area of influence of the knot). Prior to the development of the empirical relationships, a study was conducted to determine the size and distribution of knots in Douglas-fir and western redcedar poles.The validity of the technique to describe knot behavior is reflected in the ability of the finite element model to predict the strength and failure location of wood poles. The results suggested that the flow-grain analogy is a rational mechanism to quantify the fiber orientation near a knot. Furthermore, this technique could have meaningful implication in improving visual grading methods for wood poles.The authors would like to recognize the contributions of Engineering Data Management, Inc. of Ft. Collins, Colorado for their contribution of test materials and facilities for this study. 相似文献
4.
Commercial pole production in linear agroforestry systems 总被引：1，自引：0，他引：1
While the stems of upperstorey trees in agroforestry systems have many uses such as firewood and fencing, it remains true
that one incentive for growing upperstorey trees is the anticipated income generated by selling commercial quality poles.
Three hundred and ninety-one poles representing 15 tree species grown under linear agroforestry conditions at four sites in
Uganda were analyzed in terms of the length, diameter and taper of their poles. At the time of harvest, the trees were 41
months old. Although the poles varied in size and shape, none conformed to the standards observed in the commercial pole market
in Kampala. The results demonstrate that linear agroforestry systems are unlikely to produce high quality commercial poles
in a short time although they have other uses. Development of commercial pole production in these systems requires low cost
management practices. New research designs and hypotheses are needed to assess the potential of commercial pole production.
They must consider trials with larger plots, longer duration and varying management practices such as side pruning, spacing,
coppicing and pollarding. 相似文献
5.
Summary This is the first of two papers designed to describe the most recent efforts in using contemporary technology to predict strength and failure location in wood poles. In this report, a three-dimensional finite element model is presented which was developed to provide a rational stress analysis tool for wood poles. Due to practical considerations, only critical pole segments were subjected to stress analyses. Twelve-inch (30.5 cm) segments were selected for analysis which contained knots or knot clusters deemed consequential.The linear elastic model assumes small-deflection theory, and exploits linear strain, 15-node wedge and 20-node parallelepiped, isoparametric finite elements. Element geometry was selected to reflect knot size distribution found in full-size wood poles used in North America. Boundary conditions represented both applied loading and support considerations.Model verification studies were conducted on poles with isotropic (steel) and anisotropic (wood) material properties with and without spiral grain and variable longitudinal elastic properties along the pole radius. The results showed excellent agreement between theoretical and numerically-predicted pole stresses. The effect of boundary conditions on predicted stress distribution was defined, and the element geometry was appropriately modified. The developed model proved to be a rational basis for a more enhanced version to predict the mechanical behavior of wood poles with several inherent growth characteristics. 相似文献
6.
Tirusew Teshale Teshale Woldeamanuel Tsegaye Bekele Asmamaw Alemu Jürgen Pretzsch 《Small-Scale Forestry》2017,16(4):469-485
Ethiopia is one of the countries well-endowed with bamboo (Arundinaria alpine, a highland bamboo, and Oxytenanthera abyssinica, a lowland bamboo species). As compared to its potential, however, the contribution of bamboo to producer livelihoods and the national economy is very low. This paper describes the bamboo production-consumption system in the Hula district of Sidama Zone, Southern Ethiopia. Data include primary and secondary sources. The primary data were collected from 160 farmers, 38 traders and 30 consumers using household surveys, key informant interviews and focus group discussions. Data were then analyzed using a value chain analysis. In the district, all households produced bamboo and allocated on average of 1/6 of their total land holding to bamboo production. Bamboo poles, the primary products, were identified as differentiated products in the market based on length, diameter, circumference, and the intended use of the poles into four major types. In 2014, 26,825 poles of Type 1 bamboo were harvested followed by 25,269 poles of Type 2. The amount harvested from Type 3 and Type 4 bamboos were 17,661 and 20,090 poles, respectively. The value chain analysis revealed that the major actors in the production to consumption system of bamboo were farmers, brokers, wholesalers, craftsmen, house constructors and domestic users. The results indicated that each type has a distinct value chain, with differentiated pricing and use pattern. The major limiting factors identified included absence of value added production and poor market linkage. This study supports the need for further research and investment in value added production alternatives and improved market access. Policies that support farmers’ access to modern production systems, establishment of cooperatives and improved extension system will also likely to accelerate the efficiency and effectiveness of the value chain. 相似文献
7.
Summary Superposition of the longitudinal stress distributions associated with neighboring knots was used to determine the interaction distances between different knot sizes. The interaction between two knots was considered significant when the superposition of the stress distribution caused an increase in the longitudinal stress level of ten percent or more. Out of 4,374 knots measured in 44 Douglas-fir poles only 55 knots showed significant interactions with adjacent knots. However, in more than half of the poles at least one interacting knot pairs existed. Therefore, it has been concluded that stress interaction between knots could play a major role in controlling the failure of poles in bending. 相似文献
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J. Ricard 《Forest Pathology》1975,5(3):175-177
Ten, creosote treated, Douglas-fir poles infected with Poria carbonica at the ground line zone were inoculated artificially with Scytalidium sp. FY strain in January 1967. FY became established in the poles. One pole was set aside for comprehensive sampling and thirty-six samples were taken from the ground line zone of it seven years later (January 1974). One sample yielded live FY, 2 samples yielded bacteria, 9 samples showed scanty fungal growth and 24 samples yielded no microorganisms. None of the 36 samples showed advanced decay or Poria carbonica. These observations are consistent with the mechanical condition of the wood in the other 9 poles inoculated with FY after decay had begun. 相似文献
11.
Testing of poles by using acoustic pulse method 总被引：4，自引：0，他引：4
J. I. Dunlop 《Wood Science and Technology》1981,15(4):301-310
Summary Wood poles have been traditionally tested by sounding — striking with a hammer and making a subjective assessment on the basis of the sound emitted. Various other acoustic methods have been developed and employed for this function but none has been accepted on any regular basis as being successful. The propagation of acoustic waves in poles is examined here, and measurements are made using a pulse echo technique of the two acoustic parameters, velocity and damping, on a selection of poles some of which contain decay and rot. The results suggest that measurement of the acoustic damping of longitudinal compression waves may be useful in detecting the presence of decay and rot within a pole.The author wishes to thank the Council of the University of New South Wales for the allowance of Study Leave during which this work was carried out. Thanks must also be paid to Forintek Canada Corporation for their generous hospitality and to Canadian Electrical Industries and British Columbia Hydro Authority for their sponsorship of the project 相似文献
12.
林区高大母树的上树采种是一个世界性难题，本文在突破传统爬树模式的基础上，首次提出了一种新型的座式上树方式，并对该技术方案的设计原理、研究思路及其关键技术进行了较详细的论述和理论分析。座式上树设备广泛适用于林区各种母树的采种采果、森林维护以及电力部门外线作业。 相似文献
13.
The degree to which variation in species distribution is predictable from topographic variation is of considerable current interest. In this paper, canonical correspondence analysis (CCA), linear regression and principal coordinates of neighbour matrices (PCNM) models were used to explain the variation in the distributions of the 13 dominant species in a 20-ha tropical rain-forest plot in China. The results showed that: (1) Tree distribution maps show that some species are mainly found in the gullies of the plot, whereas others occur on the slopes. Which indicates topographic variables are important factors for the distribution pattern of species. (2) Both linear regression and CCA results show that convexity and elevation are the most important variables effecting distribution of trees. For saplings, elevation, convexity and aspect explain 15.3%, 9.0% and 10.1% of the total variation of species abundance. For poles, elevation and convexity explain 19.3% and 11.4% respectively. However, only 5.3% of the total variation is explained for adults. (3) The PCNM results showed that topography alone explained 20%, 24% and 5% of the total variation of species abundance for saplings, poles and adults, respectively. Overall evidence for topographic control of the tropical tree distribution is strong, but the explanatory power of topographic variables was a small part of the total of variation. 相似文献
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《Southern Forests》2013,75(3):205-213
Two popular indigenous browse, shade and poles trees, Acacia galpinii and Faidherbia albida, were evaluated for survival and growth on-farm in Malotwana, Botswana, with a mean annual rainfall of 450 mm. The trial was a two species × three spacing factorial experiment in a randomised complete block design replicated five times. The three spacings were 5 m × 5 m, 6.3 m × 5 m and 8.3 m × 5 m. The study was conducted over 6.5 years. The results showed that A. galpinii is a promising poles, browse and shade species, while F. albida exhibited high mortality (67%) at 4.5 years (after below-average rainfall). The crown width of A. galpinii ranged from 5.86 ± 0.24 m at high density to 6.56 ± 0.25 m in low-density plots. The difference in crown width among densities was significant (p = 0.0406). Diameter at breast height ranged between 10.4 ± 0.68 cm at high density to 12.5 ± 0.64 cm in low-density plantings and was significantly different among spacings (p = 0.0003). 相似文献
17.
该文以徽州考察为基础,全面阐述了徽州民间对竹资源的综合利用,从竹鞭、竹根、竹笋、竹秆、竹枝等层次进行了深入的分析,并从横向切分、纵向切分、横纵切分几个层面分析了竹秆的综合利用情况,指出民间对竹资源的利用是数百上千年的经验总结,是人民大众创造性的结晶,值得我们去研究。 相似文献
18.
Béla Keresztesi 《Forest Ecology and Management》1983,6(3):217-244
Black or common locust was introduced into Hungary between 1710 and 1720. Its present extent is 276 000 ha, 18.2% of the total forest area. Since its introduction, black locust has always been closely associated with farming.Selection breeding followed numerous steps. The best shipmast-type groves in the best stands were surveyed for superior trees which were grafted for clone tests.The National Agricultural Council for Variety Testing approved three selected or introduced locust cultivars in 1973 and five more in 1979. The registered cultivars and a further 13 candidates are grouped into three categories according to their proposed uses: sawlogs; poles and posts; and finally beekeeping and decorative planting.Some cultivars such as ‘Zalai’, ‘Kiskunsági’, ‘Császártöltési’, ‘Egylevelü’ and ‘Váti 46’ are suitable both for forestry and beekeeping.Vegetative propagation systems have been introduced for mass propagation of the improved cultivars. The planned production of 8 million plants in 1984 covers two-thirds of the demand.The selected cultivars demand intensive technologies, of which planting after deep-ploughing on better sites is the best. Silvicultural models have been worked out for producing sawlogs on better sites and poles and posts on medium sites.Interest in black locust is growing both in Europe and Asia. The area of man-made locust stands has increased in the last 20 years from 337 000 to 1 890 000 ha. These figures exclude China, where the tree is extensively used. In recent years the energy and forage aspects have become more interesting. South Korea leads in this respect, but various projects are also being undertaken in Hungary. 相似文献
19.
《Forest Ecology and Management》1986,14(2):133-140
Surveys of pole cutting in the Kimboza, Pande and Pugu Forest Reserves revealed intensities reaching 50% of available poles in easily accessible areas. Pockets of severe pole destruction were associated with pit sawing practices. No conclusive evidence for species selection was found, but emergent, canopy and smaller tree species were all affected. The implications of the findings for the survival of isolated forest fragments in Tanzania's coastal belt are discussed and suggestions are made of measures to ease cutting pressure. 相似文献