CONTINUOUS MEASUREMENT OF MOISTURE CONTENT IN GLULAM STRUCTURES
Résumé
Introduction: Today, a strong expansion of timber bridges is promoted by using glulam. The glulam bridges are widespread in Nordic countries but also in France. However, durability issues related to moisture content (MC) variation or wetting/drying cycles limit their development. For this reason, timber bridges supervisors have expressed their needs on continuous MC monitoring. The MC of wood is commonly determined by measuring the electrical resistance within pin electrodes inserted in the wood. To monitor locally MC between the lamellas of glulam, a previous study carried out in our laboratory highlighted the feasibility of resistive measurements using surface sensors embedded in glulam joints. Nevertheless, many parameters influence these measurements and need to be explored. Developments: In the present study, a series of experiments was conducted to highlight main important parameters influencing on MC measurement with surface sensors. This study focuses on "Douglas fir" which is the most used species in glulam bridges in France due to its good mechanical resistance and natural durability. Firstly, the influence of sensor-size and spacing between sensor and specimen-edge was studied. Then, the influence of temperature and MC variation on the electrical resistance of wood has been evaluated. Finally, the influence of embedded sensors inside lamellas on mechanical properties of glulam beams was also investigated. Remarks and Conclusion: The results obtained highlighted the most impacting parameters on MC measurement with surface sensors. Moreover, a calibration curve expressing the MC as a function of the electrical resistance of wood was obtained. The influence of embedded sensors on mechanical properties was also studied to validate the instrumentation of glulam beams. Future work will focus on the influence of wetting/drying cycles on mechanical integrity of glulam beams.
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