Optimal Slope of Dramix Type Fibers in Reinforced Concrete

1. Abstract Several experimental studies proved that the standard reinforcement in concrete (rebars) could be improved by short fibers to avoid local warping and cracking. In order to restrain the reinforcing rebars from corrosion, the fibers are basically at help during the curing process of concrete. Particularly in geomechanics, or foundation engineering, where one-sided moistening is expected, the reason for usage of the fibers is advantageous due to obviously irregular dehydration. The volume ratio of fibers in these cases is very low, say, about 0.5 percent. Another one interesting application is in construction of defense walls (bunkers), where the fiber ratio is principally higher. In all cases curvilinear fibers are preferred from then viewpoint of bearing capacity of the system. On the other hand, the financial expenses are also higher. This is why optimal shape design is required for maximum effectiveness of fiber reinforced concrete. Such a typical shape of current most produced fibers of this type is prepared by Dramix. This is why we concentrate our attention on straight fibers and also to the curvilinear fibers. The optimization of slope in Dramix type fibers is solved from pullout problem studied on unit cells of different arrangements. The steel fibers are considered and either linear or elasticplastic Mises material of concrete is taken into account. Mixed variational principle has been applied to enable one to formulate contact problem together with optimization of slopes. Transformation field analysis is employed to make easier the influence of nonlinear behavior of concrete. The critical pullout force is solved from finite element method and is identified from destruction of the aggregate. Several typical examples are solved to show the properties of the composite for various arrangements of fibers in cells. 2.