A procedure for calculation of optimal orthogonal reinforcement in reinforced concrete walls, slabs and shells is presented in this work. The starting point are linear elastic internal forces, determined by the finite element method. We assume the forces can cause the formation of a yield line along which the concrete cracks and the reinforcement yields. In slabs and shells there are two such lines. The forces in reinforcement and concrete are determined. The procedure is based on the lower bound theorem of plastic analysis of structures and therefore leads to safe results. In the first part walls and slabs are considered. We derive expressions for forces or couples, needed for reinforcement design. Cases where reinforcement is not needed in all directions are also considered. The presented procedure for walls is identical to the one in Eurocode 2. The standard does not include any provisions for reiforcement design in slabs. For shells an indeterminate system of nonlinear equations is obtained. The unknowns are the quantity of reinforcement at the shell top and bottom, depths of the top and bottom compression zones and orientations of the top and bottom concrete cracks. An iterative computer code is developed for the solution of the problem. Special cases in which reinforcement is not needed in all directions are taken into account. Provisions from Eurocode 2, regarding the design of reinforcement in shells, are presented. The algorithm is illustrated with some examples and compared to similar procedures and experimental results, available in literature..
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