Modelling the Material Resistance of Wood—Part 3: Relative Resistance in above- and in-Ground Situations—Results of a Global Survey

Durability-based designs with timber require reliable information about the wood properties and how they affect its performance under variable exposure conditions. This study aimed at utilizing a material resistance model (Part 2 of this publication) based on a dose–response approach for predicting the relative decay rates in above-ground situations. Laboratory and field test data were, for the first time, surveyed globally and used to determine material-specific resistance dose values, which were correlated to decay rates. In addition, laboratory indicators were used to adapt the material resistance model to in-ground exposure. The relationship between decay rates in- and above-ground, the predictive power of laboratory indicators to predict such decay rates, and a method for implementing both in a service life prediction tool, were established based on 195 hardwoods, 29 softwoods, 19 modified timbers, and 41 preservative-treated timbers

Modeling the material resistance of wood—part 2:Validation and optimization of the meyer-veltrup model

Service life planning with timber requires reliable models for quantifying the effects of exposure-related parameters and the material-inherent resistance of wood against biotic agents. The Meyer-Veltrup model was the first attempt to account for inherent protective properties and the wetting ability of wood to quantify resistance of wood in a quantitative manner. Based on test data on brown, white, and soft rot as well as moisture dynamics, the decay rates of different untreated wood species were predicted relative to the reference species of Norway spruce (Picea abies). The present study aimed to validate and optimize the resistance model for a wider range of wood species including very durable species, thermally and chemically modified wood, and preservative treated wood. The general model structure was shown to also be suitable for highly durable materials, but previously defined maximum thresholds had to be adjusted (i.e., maximum values of factors accounting for wetting ability and inherent protective properties) to 18 instead of 5 compared to Norway spruce. As expected, both the enlarged span in durability and the use of numerous and partly very divergent data sources (i.e., test methods, test locations, and types of data presentation) led to a decrease in the predictive power of the model compared to the original. In addition to the need to enlarge the database quantity and improve its quality, in particular for treated wood, it might be advantageous to use separate models for untreated and treated wood as long as the effect of additional impact variables (e.g., treatment quality) can be accounted for. Nevertheless, the adapted Meyer-Veltrup model will serve as an instrument to quantify material resistance for a wide range of wood-based materials as an input for comprehensive service life prediction software

Durability of Wood in Ground Contact – Effects of Specimen Size

The durability of wood in ground contact is affected by its material resistance on the one hand, and the exposure situation in the ground on the other hand. The latter is considered to be one of the most severe not at least due to permanent wetting and direct contact to a well-established microbial flora. In addition to physical, chemical, biological, and ecological soil parameters, the design of a wooden commodity which is in contact with the ground can have an effect on its durability. This study examined the effect of size of specimens used for in-ground durability tests. Standard EN 252 specimens, smaller mini-stake specimens, and larger double-size specimens were made from Scots pine sapwood and heartwood (Pinus sylvestris L.), Norway spruce (Picea abies Karst.), beech (Fagus sylvatica L.), and English oak (Quercus robur L.) and exposed in ground in a test field in Hannover-Herrenhausen, Germany. In addition, standard size specimens were exposed on the ground. Decay rates and corresponding durability classes according to European standards were determined. Decay proceeded slightly faster with decreasing specimen size, but for the majority of the tested materials no significant effect became apparent. However, the most durable material tested was English oak, for which durability was clearly affected by the specimen size. It was classified ‚durable’ (durability class DC 2) using double size stakes, ‚moderately durable’ (DC 3) using standard specimens, and ‚less durable’ (DC 4) using mini-stake specimens. Specimens exposed on-ground decayed significantly less rapidly compared to specimens buried in the ground to half of their length. The findings from this study recommend to use also test specimens, which are bigger dimensioned than standard specimens and thus closer in dimension to real size commodities. Otherwise, one might accept to underestimate the durability of particular wood-based materials

The effect of different test methods on durability classification on modified wood

In order to encourage increased use of wood more empirical data on the performance of wood products are needed from different exposure situations and geographical locations. In the current study modified Scots pine sapwood materials aimed treated for above ground use were compared using: 1) two different laboratory decay tests at three different climates, 2) four different laboratory moisture tests, and 3) two different field trials. The aim of the study was to investigate the effect of temperature and moisture on modified wood material performance in laboratory decay trials and to compare different durability classification methods. Lowering the temperature did slow down the decay rate, but did not make much difference in the durability ranking of the materials. The moisture behaviour of the materials in this test could not alone explain the decay resistance. The durability classification varied between the tests, confirming that the durability classification of a material, and the ranking between materials, is not a fixed value that can be based on one single test. In order to predict service life in future studies the authors recommend to combine decay and moisture data.submittedVersio

Design and performance prediction of timber bridges based on a factorization approach

Service life of timber bridges is predominantly affected by the site-specific climatic conditions in terms of moisture and temperature over time, the overall design, the design of details, and the choice of materials. In recent years, a performance-based methodology has been developed to predict (1) the material climatic conditions within timber components from macro climate data and comparison between design details, (2) decay intensity from material climate data, and (3) the material resistance as a combined effect of wood-inherent properties and its moisture dynamics. Within the WoodWisdomNet project ‘Durable Timber Bridges’ we emphasized on utilizing exposure, decay, and resistance models for a comprehensive guideline for the design of timber bridges. Therefore, a factorization approach is presented based on dose–response relationship between wood material climate and responding fungal decay. The concept does also allow for quantifying the material resistance of untreated, modified, and preservative-treated wood using factors based on laboratory and field durability tests and short-term tests for capillary water uptake, adsorption, and desorption dynamics. The findings from the present study have the potential to serve as an instrument for design and service life prediction of timber structures and will be implemented in an engineering design guideline for timber bridges

Durability of wood exposed above ground - experience with the bundle test method

The durability against decay organisms is an essential material property for wood in outdoor use. A jack of all trades method for above-ground wood durability testing has been sought for decades, but until now no method has found its way into European standardization. The method of choice shall be applicable for untreated and treated wood—ideally also for wood composites. It shall further be reproducible, objective, fast, easy, and inexpensive. Finally, it shall provide high predictive power. This study was aimed at a review of results and practical experience with the Bundle test method which could serve as a standard procedure for above-ground field tests of woodbased materials. The method allows for water-trapping, creates a moderate moisture-induced decay risk typical for UC 3 situations, and was found applicable for a wide range of wood materials. The method allows for rapid infestation and failure of non-durable reference species within five years in Central Europe. Based on results from Bundle tests with different modifications and performed at different locations, a guideline has been developed. The method is recommended as a suitable tool for determining the durability of various wood-based materials including modified and preservative-treated wood and can provide data for durability classificatio

Enhancing knowledge transfer in the wood protection sector

In order to meet the needs for the developing bio-based economy, maintaining and expanding the market potential for wood raw materials and wood products in indoor and outdoor construction uses remains a key activity for industries in the biotechnological and forestry sector respectively. A major restraint in this respect is the drastically deviating views and expectations on quality and performance of the material. Such differences can be found between producers and consumers, between architects and engineers, between planners and approval bodies as well as between academia on the one hand and industry and traders on the other hand. The wood protection and wood preservation sector is located exactly within this area of deviating opinions. To overcome the barriers due to different perceptions and therewith strengthen the standing of wood as a desirable building material in the future, new strategies and methods for communication, knowledge transfer and education are needed. Networking and scientific exchange between different disciplines is needed, such as forest science, silviculture, applied forestry, material sciences, wood technology, building technology, architecture and engineering. Consumer demands and preferences, which might serve as limit states to develop service life prediction and performance models, need to consider aesthetical aspects as well as the functionality of timber building assemblies. Finally, teaching students, craftsmen, and salesmen is the key to enhance the acceptance of renewable and carbon-storing products, which are both biodegradable and highly variable in their properties. All these peculiarities require a deeper understanding of their nature and characteristics to improve their purpose-related usage

The combined effect of wetting ability and durability on outdoor performance of wood : development and verification of a new prediction approach

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