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RC slab reinforcement design

The RC slab reinforcement design process calculates reinforcement areas for RC slabs modelled using 2D elements of uniform thickness, subject to any combination of in-plane compression and/or shear force and out-of-plane bending moment and torsion. The process ignores through thickness shear.

Two directions of reinforcement are specified; these need not be orthogonal. Reinforcement areas per unit width are calculated for each direction at the top and bottom of the slab.

To use these features, reinforcement grade needs to be defined which is referred to by concrete slab property, concrete slab property should be referred by 2D element property that include concrete material grade. Concrete design code need to be defined in design specification.


The input data for calculating reinforcement areas at a node of 2D elements include: forces and moments, reinforcement directions, section depth and concrete and reinforcement material properties.

RC slab design arrives at a solution by dividing the section into 3 layers each with a certain state of in-plane stresses. These layered stresses are in equilibrium with the applied loads. The reinforcement requirements for each layer are then calculated and apportioned to the user specified reinforcement positions.

The results consist of areas of reinforcement for the top and the bottom of the point in the two specified directions, if reinforcements cannot be calculated, empty results will be produced that indicates failure due to inappropriate input data..

Modelling implications

RC slab reinforcement design is carried out directly on a 2D element model that represents a slab or a wall. The data required additional to the analysis model data are the Concrete Slab Properties, reinforcement grade, concrete grade and the selection of an RC Slab design code. Concrete slab property may be designed before or after analysis.

The design property number in the 2D elements properties table identifies the concrete slab design property record associated with the element. Reinforcement is not calculated for elements that do not have concrete slab design properties. Refer to Concrete slab properties wizard for details of Reinforcement definition and Calculation definition.


There is no stage at which the user requests a design to be processed. Instead, when the data is correctly specified to enable the design calculations to be carried out the design results options become available. The design results are calculated only at the time they are needed for display. The Design > Check design data menu command may be used at any stage to establish whether the data has been correctly specified for RC slab design.

Reinforcement areas can be shown in graphic views as contours and diagrams, and in output views as tables of RC slab reinforcement. Areas shown with positive values represent tension reinforcement. Areas shown with negative values represent compression reinforcement.

Occasionally the process fails to produce a result for a particular point in a slab. The reason for such a failure is given in the Output view RC slab reinforcement table. Such failures are displayed in contoured output as out-of-range values, typically displayed black.

Note that punching shear is not considered: you must make separate design checks and provision for this as necessary.