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To assess the increased energy absorption capability of plain concrete under high loading rate, it is necessary to test plain concrete specimens with aggregate size near to that used in real structures using a testing methodology which allows the precise study of the softening branch of the stress-strain diagram characterised by fast crack propagation. Therefore it was decided to test large concrete specimens (cubes with 200 mm sides) with large size aggregate, developing a special equipment for the correct characterisation of the softening branch of the stress-strain diagram. The special equipment consists of input and output Hopkinson's bars subdivided into two specular bundles of elementary Hopkinson's bars. A pulse with high loading rate propagates along the bundle of the input bars, the specimen and the bundle of the output bars. During the crack propagation phase each pair of specular bars of the Hopkinson's bar bundles, which is individually instrumented with strain gauges, measures the loads and the displacements concerning only the portion of the specimen cross-section facing the cross-section of the pair of bars of the bundle. By means of the Hopkinson's bar bundle it is futhermore possible to measure moment by moment: (i) the true resisting cross-section; (ii) the true material volume under strain; (iii) the crack propagation path; (iv) the crack propagation speed. All these parameters allow a reconstruction of the true stress-strain diagram of the material up to complete separation of the specimen into two halves.

Additional information

Bibliographic Reference: Paper presented: SMIRT 13, Porto Alegre (BR), August 13-18, 1995
Availability: Available from (1) as Paper EN 39003 ORA
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