Structural Health Monitoring of glulam infrastructures with non-destructive embedded sensors

As an answer to actual environmental challenges, wood and specifically wood composites such as glued laminated timber (glulam) became a good alternative to “traditional” building materials such as concrete or steel. However, durability issues related to its environment, especially moisture, could be a imitating factor to the development of these structures. To allow glulam to be more widely used in infrastructures such as bridges we propose an embedded structural health monitoring system, measuring durability parameters in real time. It will allow a live assessment of the condition of the structure. Glulam moisture sensitivity is characterized by biological degradations at high humidity rates or cracks, delamination and internal stresses caused by humidity variations leading to a loss of mechanical properties. An integrated system, developed during two theses, allows us to record humidity rate with patch type sensors using resistive measurement method and stresses in glue joints using strain gauges, both embedded in the thickness of the glue. We are currently conducting long term experiments in real climatic conditions with loaded and unloaded beams exposed in an outdoor application to correlate the effects of real-life wetting/drying cycles combined with duration of load effects on the mechanical properties of our test samples. The running experiment started in august 2020 with 30x30x480mm model glulam beams, we are testing the bending strength of our samples to compare our results with tests conducted in climatic chamber which showed encouraging to predict the actual condition of glulam. We plan to use our data to create a predictive model to be able to determine structural performance of glulams based on live moisture measurements. This system will allow a live mapping of humidity in glulam structures, it could help glulam structures managers in preventing moisture induced pathologies and evaluating the remaining lifespan of the glulams.