Numerical modelling of the hygro-thermal response of timber bridges during their service life: A monitoring case-study

Moisture-induced stresses in large glulam beams. Case study: Vihantasalmi Bridge

“…According to Fortino et al (2013aFortino et al ( , 2019, the hygro-thermal behaviour of wood is described by the following differential equations:…”

“…The moisture content (MC) accumulated in wood for longer periods may cause, in combination with certain temperatures, conditions suitable for biodegradation of the primary material. The longterm mechanical deterioration of wood driven by cyclic variations of the environmental conditions is a challenging topic for timber bridges (Fortino et al 2013a(Fortino et al , 2019 because of the rheological properties of timber characterized mainly by mechanosorptive and viscoelastic creep. Peaks of air relative humidity (RH) above 80% in combination with high RH daily variations can cause high moisture gradients with consequent development of additional internal stresses in timber structures (Fragiacomo et al 2011).…”

“…The numerical methods for simulation of moisture transport in timber elements subjected to continuously variable climates are finalized to a more accurate knowledge on the distribution of MC in wood. The numerical methods are particularly useful for the hygro-thermal analysis of bridge elements exposed to outdoor climates along with sensorbased monitoring (Fortino et al 2013a). These methods are also suitable to evaluate the effects of MC on moistureinduced deformations as, for example, the cupping in timber decks Fjellström 2016, Pousette et al 2017).…”

“…In non-isothermal cases, also the temperature T must be taken into account as a variable of the moisture transport problem, while both the relative humidity RH and the temperature T of the air can be considered as transient field variables applied on the boundary of the wooden structure. A multi-Fickian model with wood hysteresis for timber structures subjected to continuously varying environmental conditions was implemented and tested for glulam beams of timber bridges under Southern European climates with temperature above zero degrees Celsius in Fortino et al (2013a). More recently, a multi-Fickian model with sorption dependency on temperatures above and below zero but without wood hysteresis was specialized for coated bridge components under Northern European climates in Fortino et al (2019).…”

“…Recently, there was an increasing use of multi-Fickian models for hygro-mechanical analysis of wood (Huc et al 2018, Konopka andKaliske 2018). However, to the knowledge of the authors, the large beams of timber bridges were analysed by a three-dimensional multi-Fickian modelling only in Fortino et al (2013aFortino et al ( , 2019 and the related literature by the same authors.…”