With discretization finalized for the reinforced concrete slab, the load and boundary conditions are defined as shown in Figure 49.4: Quarter Symmetric Model, Boundary Conditions and Loading.
The analysis is conducted in two steps. For the first step, an in situ dead load is generated by applying a gravitational acceleration of g = 9.81 m/s2 in the Z direction. A load-limit analysis is then performed in the second step. A surface-pressure load of 25kN is applied on the top-surface of the concrete slab and subsequently increased until the load limit is reached. The load limit is marked by a loss of numerical convergence, also identifiable as the horizontal tangent of the resulting load/displacement curve.
Due to symmetry, only a quarter of the model is included in the analysis. The symmetry regions are defined in the Mechanical Application as shown in the Figure below.
A nodal displacement constrains the model in the Z direction. This is applied to nodes on the two edges opposite to the symmetry faces. The corner node at the intersection of these edges is not selected for nodal displacement constraint.