Timber bridges - Long term monitoring results of moisture diffusion in the load carrying cross-sections

摘要

Timber road bridges have been built worldwide for centuries. The high performance of wood is approved through many constructions. However, there are still doubts about using wood by the planning engineer, which reduce the number of realized projects. The moisture induced stresses in cross-sections according to the varied ambient climate are mainly investigated under laboratory conditions. The results show that the moisture content changes differently over the cross-section and leads to moisture induced stresses. The discussion about methods for the assessment of the moisture induced stresses in timber bridge cross-ections is continuing. Results observed in the long term monitoring of seven timber bridges provide first guidelines for practitioners. For all constructions, the moisture content was measured regarding the ambient micro climate. As result, the influences according to the ambient micro climate are not insignificant. Positive is that the directly measured moisture content is less compared to the equilibrium moisture content calculated from the data of a close by meteorological station. The analysis of the moisture gradient over the cross-section allows the definition of an active or passive zone.