Modelling the Material Resistance of Wood—Part 2: Validation and Optimization of the Meyer-Veltrup Model

Abstract

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.

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

“…, are summarized in Tables 1-4. The maximum threshold (Thr) for both factors was set to 18.0, due to the best model fit obtained in Part 2 of this publication [10].…”

“…Conversion factors [9] were used when employing other reference species than Norway spruce. A more detailed description of the process for determining decay rates can be found in Part 2 of this publication [10]. The general procedure for determining and modelling decay rates for in-ground and above-ground exposure conditions is illustrated in Figure 1.…”

“…, for in-ground and above-ground exposure conditions. A more detailed edcsription of the different steps is provided in Part 1 and 2 of this publication [9,10].…”

“…In Part 1 and 2 of this publication [9,10], we focus on the counterpart of the exposure dose, which is the resistance, expressed as resistance dose, D Rd . The latter is considered to be the product of a critical dose, D crit , and two factors considering the wetting ability of wood (k wa ) and its inherent durability (k inh ).…”

“…In Part 1 of this publication [9], we performed comparative durability and moisture performance tests with Norway spruce, Scots pine sapwood (Pinus sylvestris), and European beech (Fagus sylvatica), and determined factors between the three species for the resistance against different rot types and for different kinds of moisture uptake and release. The latter allows us to utilize further data for: (1) improving and validating existing material resistance models (Part 2 of this publication [10]), and (2) generating a material resistance database for different wood species and treated timbers. Data can be gathered from current and still-ongoing, as well as historic, durability tests.…”