Two pre—tensioned I-beams, 54 ft long, produced by the long-line method in 1940 for the Ministry of Transport, have been tested by the Cement and Concrete Association at the British Railways Concrete Depot, Newton Heath, Manchester.nThe main object of the tests was to determine the loss of prestress that had occurred in 15 years, but the tensile strength of the concrete and the ultimate loads and deflexions of the beams were also measured. Strain readings, measurements of central deflexions, and visual observation, enabled the prestress remaining in the beams to be determined from the loads at which previously formed cracks re-opened.
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