**5. Conclusions**

This paper proposed the use of an advanced multi-phase numerical model for wood below the fibre saturation point, previously introduced by some of the authors, to assist the monitoring of stress laminated timber decks by integrated humidity-temperature sensors.

The hygro-thermal simulation of a representative deck volume under Northern European climates supplements the sensor-based data. The simulation provides the distribution of the moisture content below the FSP, the temperature and the vapour pressure in the studied volume and allows to draw conclusions about the hygro-thermal response of the deck. However, the model does not include the effect of solar radiation and this is a task for future research. The modelling of the protective asphalt layer is also a topic for future work. The two analysed case-studies are sheltered from rain. To consider the effects of rain and possible water traps, the current model needs to be extended by introducing the variable concentration of free water in the lumens.

In future coupled hygro-thermo-mechanical models for SLTDs, the accurate evaluation of moisture contents is important for the prediction of moisture induced stresses which are responsible for surface cracking, cupping deformations and losses of the pre-stress force in steel bars.

The proposed method can be used to assist the monitoring techniques under Nordic climates contributing to maintenance cost reduction of timber bridge decks. FEM-assisted monitoring of bridges has a grea<sup>t</sup> potential to decrease the cost of instrumentation and increase safety. It can predict possible damages and communicate the results to other infrastructure components.

**Author Contributions:** Conceptualization, S.F., P.H., L.F.; methodology, S.F., P.H., H.B., K.K.; software, S.F., P.H., K.K.; validation, S.F., P.H., A.K.; formal analysis, S.F., P.H.; investigation, H.B., K.K.; resources, T.T.; data curation, P.H., K.K., H.B.; writing—original draft preparation, S.F., P.H.; writing— review and editing, P.H., L.F., T.T.; visualization, P.H., A.K.; supervision, S.F.; project administration, S.F.; funding acquisition, S.F., T.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by WoodWisdom-Net project "Durable Timber Bridges" and by project "Delivering Fingertip Knowledge to Enable Service Life Performance Specification of Wood—Click Design", which is supported under the umbrella of ERA-NET Cofund ForestValue by the Ministry of the Environment of Finland. ForestValue has received funding from the European Union's Horizon 2020 research and innovation program. The Finnish Transport Infrastructure Agency (Väylävirasto) is a co-funder of the Click Design project.

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author. The data are not publicly available due to the agreements with the funding projects.

**Acknowledgments:** The authors wish to thank the Norwegian Public Road Administration for providing the monitoring data of Sørliveien Bridge. The Finnish Transport Infrastructure Agency (Väylävirasto) and the City of Espoo is acknowledged for supporting the monitoring of the Tapiola Bridge. The authors would like to warmly thank VTT colleagues Jukka Mäkinen, Mikko Kallio, Kalle Raunio, Pekka Halonen, Kari Korhonen for taking care of the on-going monitoring of Tapiola Bridge.

**Conflicts of Interest:** The authors declare no conflict of interest. Co-funder Väylävirasto (T.T.) participated in the interpretation of data, writing of the manuscript and in the decision to publish the results.

*kT* = 20 [W
