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1.
《Wood material science & engineering》2013,8(3-4):91-107
Abstract The need for a reliable database and a corresponding methodology to predict service life of wood and wood-based products emanates from the European Construction Products Directive, as well as from a strong interest by the building industry. A literature review on decay-influencing factors and on previous approaches to implement methods and tools for service life estimations was the basis for a concept for service life prediction of wooden components. The effect of various indirect decay factors was found to be reducible to a few direct decay factors, with material resistance, as well as wood moisture content, wood temperature and their dynamics among the key factors for fungal decay. Approaches that consider only indirect factors, e.g. climate indices, suffer from poor correlation with service life or decay rates. Therefore, the overall consideration of all possible influences, reduced on the key direct decay factors in first instance, is recommended. To fill a theoretical model with a reliable database, various data sources need to be considered, in decreasing order of priority: in-service performance, field test data, laboratory test data, survey analysis and expert opinion. 相似文献
2.
Thomas Bornemann Christian Brischke Gry Alfredsen 《Wood material science & engineering》2014,9(3):144-155
AbstractOne key issue in wood construction is durability. Constant wetting and suitable temperatures for fungal growth promote the risk of decay and thus a decrease in structural stability and performance. Hence, performance-based prediction models seem to be reasonable to predict the in-service performance of wooden structures in different outdoor exposure situations. Within this study continuous wood moisture content (MC) and temperature measurements were conducted on five different test objects. Four test set-ups were installed at a test site in Hannover, Germany. A fifth set-up was exposed in Ås, Norway. Data-sets were applied to a dose–response performance model considering wood MC and temperature as key factors for fungal decay. The expected service life (SL) was calculated for different materials and constructions. In addition, the depth and distribution of decay was assessed using a pick test and compared with the calculated SL. Differences regarding the risk of fungal decay for various construction details, exposures and materials were quantified. A wide range of SL estimates was estimated and significant differences were found between the various components, design details and wood species. Furthermore, results from the decay assessments were used to verify the performance model. Recommendations for improvements were provided. 相似文献
3.
Andreas Otto Rapp 《Wood material science & engineering》2007,2(1):15-21
The durability of wood in ground contact is affected by numerous influences, such as substrate quality, climate and microflora of the soil, which need to be considered for the prediction of service life of wooden components to be used in the ground. In this study the influence of different soil substrates on the service life of Scots pine sapwood (Pinus sylvestris L.) and oak heartwood (Quercus petraea Liebl.) was investigated. Mini-stakes were exposed in six different soils at the test site of the Federal Research Centre for Forestry and Forest Products (BFH) in Hamburg, Germany. The effect of partly embedding the test samples in concrete or polyethylene films was also examined. After 3 years of exposure the decay rates for both wood species differed significantly between the soil substrates. Compost soil and fertilized test field soil induced the highest decay activity, whereas in pure sand the lowest decay rates were observed. Surprisingly, exposure in gravel also led to higher decay ratings than sand. Protective measures by means of concrete embedding and polyethylene films performed well during the first 2 years of exposure, but showed increasing decay rates in the third year. The overall decay rating for all soil types was higher for oak heartwood than for pine sapwood. The meaning of different soils, independent of other site influences, for service life prediction of wood is discussed, and the need for further studies on this topic is highlighted. 相似文献
4.
《Wood material science & engineering》2013,8(1):15-21
Abstract The durability of wood in ground contact is affected by numerous influences, such as substrate quality, climate and microflora of the soil, which need to be considered for the prediction of service life of wooden components to be used in the ground. In this study the influence of different soil substrates on the service life of Scots pine sapwood (Pinus sylvestris L.) and oak heartwood (Quercus petraea Liebl.) was investigated. Mini-stakes were exposed in six different soils at the test site of the Federal Research Centre for Forestry and Forest Products (BFH) in Hamburg, Germany. The effect of partly embedding the test samples in concrete or polyethylene films was also examined. After 3 years of exposure the decay rates for both wood species differed significantly between the soil substrates. Compost soil and fertilized test field soil induced the highest decay activity, whereas in pure sand the lowest decay rates were observed. Surprisingly, exposure in gravel also led to higher decay ratings than sand. Protective measures by means of concrete embedding and polyethylene films performed well during the first 2 years of exposure, but showed increasing decay rates in the third year. The overall decay rating for all soil types was higher for oak heartwood than for pine sapwood. The meaning of different soils, independent of other site influences, for service life prediction of wood is discussed, and the need for further studies on this topic is highlighted. 相似文献
5.
Magdalena Kutnik Ed Suttie Christian Brischke 《Wood material science & engineering》2014,9(3):122-133
AbstractStandardization work in the field of wood durability and preservation is managed, at the European level, by the technical committee TC 38 ‘Durability of wood and wood-based products’ of the European Committee for Standardization (CEN). Producing sustainable wood-based materials is challenging. A crucial aspect of their provision is reliable standards that take consideration of both the expectations of end-users and the broad set of parameters that may influence the service life of wooden components such as exposure to moisture, climatic variations and design. In order to reach these objectives, most CEN/TC 38 standards are currently being revised based on the recent scientific, technological and legal developments in the field of wood protection. There is an increasing need for performance classification of wood products in construction and to radically consider how wood durability test methods and standards can inform on service life and how they might be translated into a performance classification system. This paper describes the changes during the past 5–10 years in Europe and how the trajectory of standards development is now on a different pathway. Classification and service life demands are described as well as current approaches to consider key issues such as material resistance, moisture risk and adaptation of existing standards. 相似文献
6.
Influence of wood moisture content and wood temperature on fungal decay in the field: observations in different micro-climates 总被引：1，自引：0，他引：1
In this study, Scots pine sapwood (Pinus sylvestris L.) and Douglas fir heartwood (Pseudotsuga menziesii Franco) specimens were exposed in double layer field trials at four different exposure sites and under different exposure
conditions (in total ten test sets). The material climate of wood in terms of wood moisture content (MC) and wood temperature
was automatically monitored over a period of 6 years and compared with the progress of decay. The aim of this study was to
highlight the interrelationship between microclimate, material climate, and decay as a basis for the establishment of dose-response
functions to be used for service life prediction of wood and wood-based products. Differences in resulting decay dynamics
between the test sites as well as between the different types of exposure were quantified and discussed with respect to corresponding
microclimatic and material climatic conditions. The time between the beginning of exposure and the first occurrence of visible
decay varied between the sites and influenced the total decay development. The fundamental importance of direct decay factors,
such as MC and wood temperature, were underlined and basic requirements for establishing dose-response-functions to be used
in service life prediction models were derived. 相似文献
7.
Comprehensive approaches to predict performance of wood products are requested by international standards, and the first attempts have been made in the frame of European research projects. However, there is still an imminent need for a methodology to implement the durability and moisture performance of wood in an engineering design method and performance classification system. The aim of this study was therefore to establish an approach to predict service life of wood above ground taking into account the combined effect of wetting ability and durability data. A comprehensive data set was obtained from laboratory durability tests and still ongoing field trials in Norway, Germany and Sweden. In addition, four different wetting ability tests were performed with the same material. Based on a dose–response concept, decay rates for specimens exposed above ground were predicted implementing various indicating factors. A model was developed and optimised taking into account the resistance of wood against soft, white and brown rot as well as relevant types of water uptake and release. Decay rates from above-ground field tests at different test sites in Norway were predicted with the model. In a second step, the model was validated using data from laboratory and field tests performed in Germany and Sweden. The model was found to be fairly reliable, and it has the advantage to get implemented into existing engineering design guidelines. The approach at hand might furthermore be used for implementing wetting ability data into performance classification as requested by European standardisation bodies. 相似文献
8.
Scots pine sapwood (Pinus sylvestris L.) and Douglas fir heartwood (Pseudotsuga menziesii Franco) specimens were exposed in double layer field trials at 23 different European test sites under different exposure
conditions (in total 27 test sets). The material climate in terms of wood moisture content (MC) and wood temperature was automatically
monitored over a period of up to 7 years and compared with the progress of decay. The overall aim of this study was to establish
dose–response relationships between climate factors and decay as a basis for the service life prediction of wood. The “Scheffer
Climate Index” based on weather data collected at official meteorological stations at the different test sites poorly correlated
with the corresponding decay progress and was therefore not a suitable tool for estimating site-specific decay potential.
In contrast, the use of the combined material climatic parameters MC and wood temperature led to a feasible dose–response
function and turned out to be a useful basis for service life prediction of wood. 相似文献
9.
David Lorenzo Juan Fernández-Golfín Manuel Touza Alfonso Lozano 《Wood material science & engineering》2020,15(3):123-129
ABSTRACTThis article shows the performance of spruce bridge that represents the situation of several wooden bridges built in the 1990s in Spain with spruce and fir. In most cases, damages due to severe decay had appeared before 10 years of service life, and the magnitude and extent of the damages were so significant that the substitution of the structures became mandatory. The aim of this study is to understand the causes of early and severe decay, showing the case study of a spruce bridge located in north-west Spain and analysing the influence of wood species, preservative treatments and designs, combined with the variability of environmental conditions in the emergence of early pathological processes. The damage of the elements is related to the wood species used, the impossibility of applying a preservative treatment, the climatic conditions and local climate, bad design details and no maintenance, which result in a prolonged time of wetness during most of the year. This example confirms the inability of spruce wood for being used in exterior structures, such as bridges, which are located in wet and warm climates like north-west Spain and having wood-destroying fungi that can degrade the wooden elements. 相似文献
10.
The majority of timber products in outdoor use are exposed above ground, e.g. façades, terrace decking, playground equipment, garden furniture, windows, balconies or carports. In contrast, the durability of wood and wood products is most often determined in laboratory against Basidiomycete monocultures or in-ground field tests, where wood samples are submitted to permanent wetting. Worldwide, only a few above ground field test methods evaluating durability against fungal decay have been standardized. Wood used in above ground situations can be exposed to a wide range of moisture loads reflecting different design details such as varying shelter, distance to ground, ventilation and water trapping, whereas temperature and rainfall variations are overall influences on service life performance. The aim of this review was to gather information about standardized and non-standardized above ground field test methods used to determine the durability of wood and wood-based products. In total, more than 60 methods have been evaluated according to different criteria, such as principle set-up and design, severity of exposure and distance to ground. Their suitability to reflect a certain exposure under real-life conditions is discussed as well as practical aspects regarding acceleration measures, decay assessment and practicability, costs and time efforts. 相似文献
11.
文章在大量详实的基础数据和实地调查基础上,运用多种生态经济学方法,包括市场价值法、旅游费用法和影子工程法等,将南湖湿地公园生态系统服务功能分为具有直接使用价值的生产产品功能和具有间接使用价值的生命支持系统功能进行评估。结果表明,直接使用价值(包括提供生态系统产品功能、休闲娱乐功能)约为2.49×106元;间接使用价值(包括水资源调节功能、生物多样性功能、水质净化功能、大气调节功能、文化科学功能等)约为2.07×108元,间接价值远远大于直接价值。 相似文献
12.
木材是人民生活及国家建设中必需材料，其需要量极大，但树木生长期长，形成供需矛盾尖锐。新世纪中可应用生物技术中基因重组、细胞融合、固定化酶组织等方法，再结合当前计算机、生物化学、电子技术学等学科渗入到木材工业后，必将使树木生长期缩短，增加木材资源。随保护木材措施增加、木材使用寿命的延长，并且在木材加工中工艺不断改进，增加产品，提高木材综合利用率，从而促进木材工业的发展。 相似文献
13.
《Scandinavian Journal of Forest Research》2012,27(2):121-132
Abstract A life cycle assessment (LCA) of residential windows was conducted to evaluate the environmental impacts of those made with aluminum-clad wood, polyvinyl chloride (PVC) and fiberglass frames for sale in North America. The LCA was a case study in which specific-site data were used for the manufacturing stage of each window, while published data were adapted to complete the life cycle inventories using Sima Pro software. These inventories were grouped into impact categories and scaled based on IMPACT 2002+ version 2.1 characterization and damage factors. The damage modeling indicated that the life cycle impacts are dominated by the combustion of non-renewable energy resources. The PVC life cycle used the most non-renewable energy and caused the most damage owing to that window's shorter service life. The disposal of aluminum cladding in the municipal waste stream caused greater aquatic ecotoxicity for the wood window. The sensitivity analysis revealed that replacing the virgin material in aluminum cladding with recycled content improved the life cycle impacts of the wood window. Using fiberglass or PVC to clad the wood window also improved the environmental performance. Other potential improvements to the life cycle impacts of the three windows include improving energy efficiency, particularly during the secondary manufacturing. 相似文献
14.
Local damage such as knots, decay, and cracks can result in a reduction of service life due to mechanical and environmental
loadings. In wood construction, it is very important to evaluate the weakest location and to detect damage at the earliest
possible stage to avoid future catastrophic failure. In this study, modal testing was carried out on wood beams to generate
the first two mode shapes. A novel statistical algorithm was proposed to extract the damage indicator by computing the local
modal flexibility before and after damage in timbers. Different damage severities, damage locations, and damage counts were
simulated by removing mass from intact beams to verify the algorithm. The results indicated that the proposed statistical
algorithm is effective and suitable for the damage scenarios considered. The algorithm was reliable for detecting and locating
local damage under different damage scenarios. The peak values of the damage indicators computed from the first two mode shapes
were sensitive to different damage severities and locations. This approach was also reliable for detecting multiple defects. 相似文献
15.
The fatigue life of structural plywood under two-stage panel shear load was experimentally examined. Two experimental conditions
were determined for two-stage fatigue of plywood specimen: one used variable applied stress and the other used variable stress,
loading waveform, and loading frequency, because fatigue life of wood composite under constant load depended on loading waveform
and loading frequency as well as stress level. The most famous cumulative fatigue damage theory is the Palmgren-Miner rule,
which is the summation of the ratio of the applied loading cycle to the fatigue life under each loading stage. However, the
applicability of this rule to the two-stage fatigue of wood composites has not been investigated. It was first demonstrated
in this study that the fatigue life of the plywood specimen reached in the two-stage fatigue test did not obey the Palmgren-Miner
rule. Here, we propose the new cumulative fatigue damage model by modification of the Palmgren-Miner rule on the basis of
the assumption that fatigue damage accumulates with loading cycle on a logarithmic scale. The newly proposed model was in
good agreement with the fatigue life reached in the two-stage fatigue test. 相似文献
16.
A statistical algorithm for comparing mode shapes of vibration testing before and after damage in timbers 总被引：3，自引：0，他引：3
Instances of local damage in timber such as knots, decay, and cracks can be translated into a reduction of service life due
to mechanical and environmental loadings. In wood construction, it is very important to evaluate the weakest location and
to detect damage at the earliest possible stage to avoid future catastrophic failure. In this study, modal testing was used
on wood beams to generate the first two mode shapes. A novel statistical algorithm was proposed to extract a damage indicator
by computing mode shapes of vibration testing before and after damage in timbers. The different damage severities, damage
locations, and damage counts were simulated by removing mass from intact beams to verify the algorithm. The results showed
that the proposed statistical algorithm is effective and suitable for the designed damage scenarios. It is reliable for the
detection and location of local damage of different severities, location, and number. The peak values of the damage indicators
computed from the first two mode shapes were sensitive to different damage severities and locations. They were also reliable
for the detection of multiple cases of damage. 相似文献
17.
在机械和环境荷载作用下,木质构件和结构的局部缺陷如节疤、腐朽和裂缝等会导致使用寿命的缩减.在木结构工程领域,如果能够尽早对结构和构件的最薄弱位置进行检出和评估,可避免因突然破坏而导致的灾难性事故.在本研究中,通过振动测试获取前两阶模态振型,并利用锯材梁损伤前后的模态柔度矩阵差值曲率提出损伤识别指标.为了验证提案损伤指标的有效性,通过人工切除截面质量来模拟不同损伤程度、不同损伤位置和双数个损伤的情景,试验结果表明损伤指标对不同程度、不同位置和双数个损伤均能准确定位,并可对损伤轻重程度进行定性评价. 相似文献
18.
The local damages such as knots,decay, and cracks can be translated into a reduction of service life due to mechanical and environmental loadings.In wood construction,it is very important to evaluate the weakest location and detect damage at the earliest possible stage to avoid the future catastrophic failure.In this study,the modal testing was operated on wood beams to generate the first two mode shapes.A novel statistical algorithm was proposed to extract the damage indicator by computing the modal flexibility curvature before and after damage in timbers.The different damage severities,damage locations,and damage counts were simulated by removing mass from intact beams to verify the algorithm.The results showed that the proposed statistical algorithm was effective and suitable to the designed damage scenarios.It was reliable to detect and locate local damages under different severities,locations,and counts.The peak values of the damage indicators computed from the first two mode shapes were sensitive to different damage severities and locations.They were also reliable to detect the multiple damages. 相似文献
19.
Bohumil Kasal 《Wood material science & engineering》2014,9(3):134-138
AbstractThe in situ assessment of timber structures has gained considerable attention in recent years due to some unexpected failures of public buildings. The assessment of timber, however, has been used in the evaluation of historic structures for a number of years, and the methods employed have evolved from visual observation (which is still one of the most effective ways of evaluating in situ timber) to more sophisticated methods that use various physical phenomena such as stress-wave or X-ray energy attenuation. In the health assessment of timber, effects of biotic elements such as insects and fungi are of interest, which, of course, is always connected with the presence of water in wood. The structural assessment encompasses questions related to the structural integrity of in situ members and the performance of components and the system. The structural health assessment not only focuses on biotic elements but also attempts to quantify engineering properties of the material such as strength degradation, modulus of elasticity, loss of cross-section, extent of checks, and other quantitative parameters needed for subsequent evaluation of the structural system, frequently expressed as load-bearing capacity. Service life planning of a structure is a complex issue that is related not only to the materials but also the environment and the use of the structure. Assessment of the health and properties of existing timber elements yields a piece of information that is necessary but not sufficient for the service life estimate. In the evaluation of structural timber, a mere use of various assessment techniques is not sufficient and usually an involvement of disciplines such as wood anatomy, wood physics, and statistics is needed. A reliable estimate of the parameters of in situ timber requires careful planning of measurements (experiments) since the material is highly variable and any statement about the properties of an element or even the entire system must reflect the random character of the wood properties. This paper will summarize the state-of-the art methods used in the assessment of in situ timber and analyze the strengths and the weaknesses of selected methods. An attempt will be made to outline future directions in the development of in situ assessment methods. 相似文献
20.
Andreas Krause 《Wood material science & engineering》2014,9(3):179-185
AbstractWood polymer composites (WPC) consist mainly of wood particles from non-durable softwoods. From experience in service life and laboratory testing it is known that WPC is not fully resistant against biological attack. Concerning durability testing, it is difficult to reach sufficient moisture content for fungal growth in the time frame of testing. Furthermore, the interpretation of test results is difficult, since the mass loss is measured but strength loss might be more important during service life. The relation between mass loss and strength loss is not deeply explored so far. Additionally moisture uptake causes an irreversible strength loss of WPC. Considering these problems a new test method for investigating the resistance of WPC against basidiomycetes is described in prEN 15534-1. In this paper, several test methods were carried out regarding their suitability for durability testing of WPC. The tests included various pre-wetting methods. After durability testing the mass loss and changes in strength and stiffness were evaluated. The results have shown that pre-wetting according to EN 84 is suitable to increase the moisture content. Furthermore strength and stiffness loss is higher than mass loss. The loss in mechanical properties is based on moisture uptake as well as fungal decay. 相似文献