CONCRETE REINFORCING NET: OPTIMUM SLIP-FREE LIMIT DESIGN

The proposed slip-free design assures desired safety against large frictional shear slip of crack surfaces, which assures a reduced extent of cracking and damage to concrete. Orthogonal nets in shell or plate walls under in-plane forces are considered. A reinforcement that is up to about 34% heavier is obtained when large shear forces in the bar directions are present. The case when one principal force is compressive is also analyzed, and here the differences become still larger (up to about 67%). The optimum classical (frictionless) limit design is found to be equivalent to the optimum service stress design (except for a common scaling factor), which is an objectionable feature, and the difference between them is due soley to safety factors. In the slip-free design, which is almost as simple as the frictionless design, the critical crack direction leading to the lightest possible reinforcement is not at a 45 degree angle with the bars, as in the frictionless design, but deviates from it substantially. The safe domain in the plane whose coordinates are the reinforcement ratios is still a hyperbola, but with inclined asymptotes.