*Article* **Health Monitoring of Stress-Laminated Timber Bridges Assisted by a Hygro-Thermal Model for Wood Material**

**Stefania Fortino 1,\*, Petr Hradil 1, Keijo Koski 1, Antti Korkealaakso 1, Ludovic Fülöp 1, Hauke Burkart 2 and Timo Tirkkonen 3**


**\***Correspondence: stefania.fortino@vtt.fi; Tel.: +358-40-579-3891

**Abstract:** Timber bridges are economical, easy to construct, use renewable material and can have a long service life, especially in Nordic climates. Nevertheless, durability of timber bridges has been a concern of designers and structural engineers because most of their load-carrying members are exposed to the external climate. In combination with certain temperatures, the moisture content (*MC*) accumulated in wood for long periods may cause conditions suitable for timber biodegradation. In addition, moisture induced cracks and deformations are often found in timber decks. This study shows how the long term monitoring of stress-laminated timber decks can be assisted by a recent multi-phase finite element model predicting the distribution of *MC*, relative humidity (*RH*) and temperature (*T*) in wood. The hygro-thermal monitoring data are collected from an earlier study of the Sørliveien Bridge in Norway and from a research on the new Tapiola Bridge in Finland. In both cases, the monitoring uses integrated humidity-temperature sensors which provide the *RH* and *T* in given locations of the deck. The numerical results show a good agreemen<sup>t</sup> with the measurements and allow analysing the *MC*s at the bottom of the decks that could be responsible of cracks and cupping deformations.

**Keywords:** timber bridges; stress-laminated timber decks; monitoring; humidity-temperature sensors; wood moisture content; multi-phase models; finite element method
