The use of epoxy resin adhesives in structural engineering is introduced with particular reference to the strengthening of bridge decks. A review of the fatigue and creep characteristics of structural adhesives is then presented by reference to previously published work. It is noted that much of the past research has been conducted with aerospace or vehicle applications in mind. Nevertheless, this can provide useful guidance. The report summarises a number of extra-mural research contracts placed by the Transport and Road Research Laboratory (TRRL) in the 1980s to investigate various aspects of the performance of epoxy resin adhesive joints. In particular this work encompassed both fatigue and creep testing over the range of temperatures likely to be encountered at bridge sites in the UK. It involved fatigue testing and creep testing for up to one year using double lap joints constructed with three varieties of cold-cure and one hot-cure adhesive. It also considered the effect of low curing temperatures and two alternative accelerated ageing regimes. The fatigue and creep performance of bonded joints is temperature dependent. There is a significant reduction in strength as the temperature reaches the transition temperature, which for the cold-cure products occurs between 40 and 50 degrees C. Thus, the use of cold-cure adhesives is not recommended at service temperatures in excess of 40 degrees C. Further, curing at temperatures below 10 degrees C is unlikely to be acceptable. The stress range in cold-cure joints should be limited to 4.0 Newtons per square millimetre and that in hot-cure joints to 7.1 to prevent fatigue failures during the 120 year design life of a bridge. In addition the sustained stress in an adhesive bonded joint should be kept below 25% of the short term strength in order to prevent failures due to creep rupture during the design life of the structure. Any assessment for application of bonded connections in bridge or other structures must take into account the design spectrum of loads, the variation in fatigue and creep strength with temperature, the duration of exposure at different temperatures and the environmental and climatic conditions during service. (A)

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