The recent innovation of using stress absorbing layers behind the abutments of an integral bridge may offer a means of reducing the seasonal build up of lateral pressures caused by thermal expansion of the deck. Following the decision to use this technique at Mount Pleasant Flyover, an opportunity arose to carry out an instrumented case history study to evaluate the performance of the stress absorbing layers. After earlier laboratory and pilot scale trials, a layer of polyethylene foam was placed behind one abutment and a layer of recycled rubber crumb sheet behind the other. Performance monitoring was carried out during the construction period and for just over three years in service. Measurements were taken of changes in deck length, strains and temperatures in the deck, lateral earth pressures acting on the abutments, changes in the thickness of the stress absorbing layers and settlement behind the abutments. The implications of the findings upon the design procedures for integral bridges are discussed.

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