**4. Discussion**

The combination of the sensor-based monitoring and numerical model presented in the previous sections, allowed analysing the hygro-thermal response of the uncoated SLTD of Sørliveien Bridge in Norway and the thick painted SLTD of Tapiola Bridge in Finland. In addition to the temperature *T* and vapour pressure *p*v, the numerical model was able to provide quantitative values of the moisture content *MC* and the moisture gradients trends close to the surface that could be responsible of surface cracks, as shown in earlier works for large glulam beams of timber bridges [10–12] and in a research on the monitoring of large span timber structures [36]. In particular, we analysed the bottom part of decks which are sheltered from rain but subjected to both the continuously variable air humidity and temperature.

The uncoated deck of Sørliveien Bridge in Norway was analysed as a first case-study, and showed a relatively stable moisture behaviour after one year from the bridge erection. The main findings are listed below:


The painted and thick deck of Tapiola Bridge was analysed as second case-study, starting from an earlier stage after construction. The main findings are the following:


The following observations are based on the comparisons between the two case-studies:


The displacements and forces measured in the other sensors of the two monitoring systems can be simulated in future work by integrating the hygro-thermal analysis with a mechanical model for wood as in [9,12].

The embedded sensors and computational unit allow further expansion of the Internet of Things (IoT) network in order to efficiently exchange the monitoring data with passing vehicles and stationary objects of the road infrastructure. Moreover, combined with the results of the FEM simulation, the system can provide a comprehensive understanding of the bridge deck conditions in real time.
