Experimental Investigation on Time-Dependent Flexural Crack Growth

Abstract

The experimental investigation concerns to the behaviour of plain concrete beams with a single notch under sustained loading. The notch is located at the bottom in the middle of the beam. In order to get insight into the short-term capacity of the beams, nine specimens were tested in short-term loading. The experimental program comprised four specimens in cast I, five specimens in cast II, six specimens in cast III, five specimens in cast IV and six specimens in cast V. The test results comprise of measured material characteristics such as development of concrete compressive strength. The measured crack width and crack length are given for each specimen. The crack width (at notch tip), the notch opening (at mouth of the notch), the deflection in midspan and the applied force were measured and registered continuously. In cast I, three specimens were tested in short-term loading and one specimen was tested in long-term loading under 90% of the average ultimate short-term capacity measured in the former tests. However, the latter specimen failed under a load equal to 88% of the average short-term capacity. In cast II, three specimens were tested in short-term loading and two specimens were tested in long-term loading under 80% and 73% of the average short-term capacity. The former failed when it reached the desired load (80%) and the latter failed after 16 hours which gave the only time-dependent result in this test series. In cast III, two specimens were tested in short-term loading and two specimens were tested in long-term loading. The load ratios of tested specimens were 71% and 83% of the short-term capacity. The beam with the highest load failed after 3,5 hours and the other failed after 14 days. In cast IV, one specimen was tested in short-term loading and four specimens were tested in long-term loading, one of which failed during load application. The load ratios were chosen to be 71,5 and 77%. In cast V, all of the specimens were tested in long-term loading, with different load ratios between 65% and 73%. Later, the crack rate dependency of the tested specimens was analysed and a viscoplastic model by means of ‘Generalised Burger’s model’ was proposed in order to the creep data.