Durability of rain-exposed timber bridge joints and components

• The design of details is an important aspect in durability design of rain-exposed timber structures. Joints are considered the weak-points of these structures as they accumulate moisture and facilitate deterioration by decay. The present study aims to study the influence of detail design, and its effect on the service life, by estimating the decay rate in a number of rain-exposed timber components and joints, typically found in timber bridges. A test-setup was exposed outdoors over a period of one year while the moisture content was measured in specific measuring points. The test-setup included groups of beams, columns and joints commonly found in timberbridges. For the beams and columns, the effectiveness of typical protective measures was also tested. The annual decay rate was estimated using two different decay prediction models. Compared to a reference beam, the results show that structural protection reduced the risk of decay while joints and end-grain tended to be at increased risk. The lowest service life, estimated to 3-4 years, was found close to end-grain where drying was hindered but moisture could accumulate. In general, the discrepancy between the two decay models was large for low to medium exposure and decreased with increasing exposure.

Nyckelord

Decay

Durability

Performance model

Timber bridge

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