TRRL is undertaking a research programme to re-examine the present method of assessing the traffic load carrying capacity of brick and masonry arch bridges (normally referred to as the MEXE method). The programme consists of full scale and model scale load tests to collapse, and theoretical analysis. This report describes the third and fourth in the planned series of about ten full scale tests. Both bridges were canal bridges with similar spans and rises. In most other respects they were dissimilar. Preston bridge was substantially built with an elliptical sandstone arch 360 mm thick and brick spandrel walls and parapets. Prestwood bridge had a brick segmental arch only 220 mm thick. It was in poor condition, with parapets removed and a distorted arch. Load was applied at road surface level on a 'line' the full width of the bridge at 1/3-span and 1/4-span respectively. Preston bridge collapsed due to crushing of the arch ring beneath the load line after a maximum load of 2110 kN was applied. Prestwood bridge collapsed as a 'four hinged mechanism' after a maximum load of 228 kN was applied. The report compares the results of the tests with theoretical analyses and a model test.

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