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UBC Theses and Dissertations

Investigation of the dynamic fracture behavior of concrete Somaskanthan, Nadarajah


Impact tests on plain and steel fiber-reinforced concrete beams, with varying length and notch depth, have been carried out using a drop weight impact machine and a fast data acquisition system. The rate dependant dynamic behavior as well as the relative performance of plain and fiber-reinforced concretes have been studied. It was found that during the dynamic test data acquisition process, the use of analog filters give erroneous results, which was detected by the crack gauge employed in this study. When using the analog filter, the event time increased and the peak signal value decreased considerably, relative to the unfiltered or true values. The inertial loads associated with the specimen during the impact event were evaluated on the basis of structural dynamic principles. The raw dynamic signals have been analyzed in the frequency-domain, and the dynamic characteristics of the system and specimen have been identified. Corrections for signal filtering and static load calibration have then been carried out. In general, it was found that plain concrete is strain rate sensitive. The relationship between log of crack velocity and log of dynamic fracture toughness, KJDC, is linear with two distinct regions of applicability. The KJDC depend on notch depth as well as span length, indicating a geometrical dependency. The comparison based on span length showed that the shear effect will be predominant at shorter span. Although the crack velocity is affected by the inclusion of fibers, the dynamic fracture toughness for plain concrete and fiber-reinforced concretes have been found to be the same at all strain rates. However, the effect of the fibers on the toughness of the fiber-reinforced materials may have been masked by the large variability in the data.

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