Limit States Design of Slabs Using Lower Bound Approach

Simple expressions are given for the calculation of lower-bound yield moments for rectangular, orthotropically-reinforced concrete slabs under uniform load. Using these results, a limit states design method is developed. In this method, the areas of tension reinforcement required per unit width of the slab are designed for the calculated yield moments, using ultimate strength design provisions given in the codes. The positive reinforcement is provided throughout the slab; and the negative reinforcement must extend at least over the regions suggested in the paper. The serviceability requirements of the slab are satisfied by choosing the thickness of the slab to fulfill deflection requirements specified in the codes and by selecting the diameter of the reinforcing bar to satisfy the crack-control criterion developed in the paper. Simple expressions are also given for the calculation of edge-beam forces. The design method is illustrated by a numerical example.