Material Degradation with Moisture Transport Mechanisms in Timber Bridge Decks: Finite Element Modeling

Abstract

The structural longevity of timber bridge decks is inherently governed by the complex interplay between environmental exposure and the fundamental hygroscopic nature of wood. Material degradation in these structures is rarely the result of immediate mechanical overload, but rather a progressive deterioration facilitated by long-term moisture transport mechanisms. This paper investigates the spatial and temporal distribution of moisture within timber bridge decks and evaluates the subsequent material degradation using advanced finite element modeling techniques. By simulating the anisotropic diffusion of water through the porous cellular network of the wood, the study captures the transient moisture gradients that develop under cyclic environmental loading. A coupled hygro-mechanical framework is employed to assess how localized elevations in moisture content initiate stiffness reduction and promote conditions conducive to biological decay. The computational results demonstrate that moisture accumulation is highly concentrated at connection points and interfacial gaps, creating persistent high-moisture zones that significantly accelerate localized degradation. The finite element modeling evidence underscores the necessity of considering non-Fickian diffusion characteristics and moisture-dependent mechanical properties in the structural assessment of timber bridges. These findings provide critical insights for optimizing preservation strategies, informing maintenance schedules, and enhancing the overall resilience and service life of sustainable timber infrastructure globally.