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Wood is a hygroscopic material and can absorb or release moisture from the surrounding climate. The wood moisture content (MC) influences the material strengths and stiffnesses as well as the long-term load-bearing behaviour. For this reason, the continuous monitoring of wood moisture content is a suitable early warning system to increase the quality of wood structures in a pioneering way and to detect changes in time. The paper presents several suitable measuring methods for the MC and explains their advantages, accuracies, and applications. The explanations are supported by case studies.

<p>Timber road bridges have been built worldwide for centuries. The high performance of wood as structural material is approved. However the influence of moisture induced stresses in cross sections according to the varied ambient climate are still questioned. Results observed in the long term monitoring of six timber bridges provide first guidelines for practitioners. Further on, first numerical simulations are carried out for the assessment of the long term behaviour of timber bridges over the life cycle. The numerical simulations include the moisture diffusion transport in wood as well as the resulting stress strain behaviour of the timber member. The research results provide new guidelines for the planning engineers, the definition of an active or passive zone of the cross sections, and provide a differentiation of the service class over the cross section.</p>

Wood is a hygroscopic material that primarily adapts its moisture content to the surrounding relative humidity. The climate in a structure or building depends on the building type and the region the structure is located in. In this study, the effect of region on the moisture content of wood was investigated. Measurements taken in 12 ventilated timber structures were compared to the theoretical equilibrium moisture content calculated from the relative humidity and temperature in 107 meteorological stations across Switzerland. The monitored load-bearing elements were made of softwood and protected from the direct impact of weather. The climatic conditions around the Alps, a mountain range that runs from France to Austria and crosses Switzerland, can be divided into the following three different regions: (1) south of the Alps, where the climate is affected mainly by the Mediterranean sea; (2) north of the Alps, where the climate is affected by the Atlantic Ocean; and (3) the inner Alps, where the climate is considered to be relatively dry. The climatic conditions of the three separate regions were reflected in the measurements made in the monitored timber structures. Differences between the regions were quantified. The moisture content and relative humidity, similarly to temperature, depended on altitude (above sea level).

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