| Summary: | The objectivc of this research was to determine the in-plane shear stiffness and strength of a reinforced concrete sprecimen, which had first been cracked in uniaxial tension. This information could then lead to a more accurate analysis or reinforced concrete structures using the finite clement method. Tests were devised that enabled the effects of aggregate interlock and of dowel action in slab type specimens to be studied independently. As the aggregate interlock and dowel action specimens were similar and were loaded in the same way, a direct comparison of the test results could be made. The composite effects of aggregate interlock and dowel action were then studied by applying the same shear loading to cracked reinforced concrete specimens. The shear stiffness and strength due to aggregate interlock were typically found to be two to four times as great as those due to dowel action. It was also observed that the crack in the aggregate interlock tests tended to widen as shear slip occurred. This is an effect which has received very little attention in the past. The stiffness normal to the crack that restrains crack widening, and the initial crack width were both observed to have a significant influcnce on the aggregate interlock shear stiffness. The behaviour of the reinforced concrete specimens was similar to that which was expected from the results of the dowel action and aggregate interlock tests, if the additional effects of local bond were LikclI into consideration. Several analytical models of the micro mechanisms of shear resistance within the specimens were studied and formulae were derived to predict their behaviour. A matrix equation for the material properties for cracked concrete was derived and used in a finite clement analysis in an attempt to model the behaviour of a reinforced concrete structure.
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