Case studies: long-term monitoring of timber bridges

Timber bridges are subjected to climatic changes respectively cycles which result, due to the hygroscopic material behavior, in a change of the moisture content in the wood and thus change of dimensions of the wooden elements. But there is still missing knowledge about the impact of the climatic changes. Thus, the objective was to investigate the material behavior due to climatic changes regarding the moisture content and dimensional changes in relation to the natural material axes and within the cross section. Therefore different traffic timber bridges with big cross sections were long-term monitored within a research project. The results of the moisture contents measured and a comparison between the different measuring points as groups and at different positions are presented. The results confirm that the wood moisture content follows the climatic changes delayed and with smaller amplitude compared to the calculated equilibrium moisture content. It was observed that the change of the moisture content differs over the cross section and along the span of the members. Moreover, due to the monitoring systems, a damage of the bridge could be detected at an early stage and further damage could be prevented.