Health monitoring of stress-laminated timber bridges

Timber bridges are economical, easy to construct, use renewable material and can have a long service life in Nordic climates like in Finland or Norway. However, failure modes and degradation mechanisms of timber bridges are different from those made of conventional materials like concrete and steel, and wood degradation mechanisms are also less studied. Durability of timber bridges has been a concern of designers and structural engineers due to the fact that the majority of their load-carrying members are usually directly exposed to the external climate. The moisture accumulated in the material for longer periods may cause (in combination with certain temperatures) conditions suitable for biodegradation of the primary material. The present study uses long term monitoring data from stress-laminated timber decks in Nordic climate conditions to develop suitable finite element model to predict moisture content and temperature inside of the wood members. We present the monitoring system of a recently opened timber bridge with a stress-laminated deck in the city of Espoo, Finland. The bridge is a highway crossing with two spans, serving local car and bus transportation. The monitored quantities are moisture and temperature in wood, displacement at supports, and force fluctuations in the pre-tension bars. The bridge is equipped with five moisture & temperature sensors, two displacement (vertical and horizontal) and two force sensors. The measurements will supply further calibration data for the present hygro-thermo-mechanical model.