For plate and shell elements supported at points or by linear supports (by means of the available support types, columns or walls), values of moments and stresses near the support points may be considerably greater than at the remaining points of the plate. This may cause calculation of incorrect reinforcement in the vicinity of supports and columns. To avoid this, such connections can be modeled either by means of the available rigid links or by applying Reduction of forces above columns and walls.
Reduction of values near supports replaces the result values obtained in the vicinity of supports, columns and walls with the reduced value from the vicinity of these supports. Three stages are distinguished in this operation.
Definition of support nodes. Values are reduced only near supported defined as follows.
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A column type support (rectangular or round) with non-zero dimensions - See advanced parameters for supports.
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A linear support on the edge or on a polyline. This support is defined as a wall in advanced support parameters.
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Member elements are connected with finite elements. This is only when the other member end is not connected with the same finite element as it is the case for a strengthening beam. For a node to be considered as supported, it must be adjoined by at least one finite element.
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Planar elements of the horizontal panel meet with planar elements of the adjoining perpendicular panel (a vertical wall in the Z direction) on a horizontal panel (a slab in the XY plane).
At nodes where supports at points and beam supports (without dimensions) are defined, values are not reduced.
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Definition of a reduction radius. If reduction of selected values is performed at a given node, then it should be determined which values should be disregarded. The values ignored include the values at this node and at centers of elements that adjoin this node. The software searches for nodes positioned in the distance lesser than the reduction radius; values at these nodes are also disregarded and replaced with the calculated average value. The reduction radius is determined in the following way.
- Supports defined at a node. Reduction radius equals half the length of the diagonal of a rectangular support, or half a diameter of a round support plus 0.2*(maximum thickness of an element adjoining the support node).
- Columns adjoining a node. Reduction radius equals half the length of the diagonal of a rectangle with dimensions equal to the column width and height plus 0.2*(maximum thickness of an element adjoining the column node).
- Linear support defined on the edges or using polylines. Reduction radius equals half the linear support thickness.
- Adjoining perpendicular panel. Reduction radius equals half the wall thickness.
If one node is adjoined by several supports with different values of reduction radiuses, then the greatest of the calculated radiuses is adopted in calculations.
Calculation of the reduced value for a column type support - When the reduction radius value is calculated, the result values in nodes positioned in the distance (from the supported node) lesser than the determined radius value and in centers of finite elements that adjoin them are disregarded. These values are replaced with the reduced value of the results on the edge of the disregarded region. When calculating this value, the averaging parameters are taken into account. If a node is adjoined by an element and at least one of this element's nodes lies inside the reduction circle, then a value from this element is also ignored while averaging. The reduced value is calculated by applying the following principles.
- If values at all nodes on the edge are positive, then the maximal value is adopted.
- If values at all nodes on the edge are negative, then the minimal value is adopted.
- If values on the edge show different signs, then the average value is calculated and that value is assumed as the reduced one.
Calculation of the reduced values for linear / wall type supports - reduced value is read from the last nodes located inside the linear / wall support contour - looking in the direction from the center outward (conservative approach).
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If values at all nodes are positive, then the maximal value is adopted.
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If values at all nodes are negative, then the minimal value is adopted.
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If values at nodes on opposite sides show different signs, then the average value is calculated and that value is assumed as the reduced one.
When the reduced value is calculated, it substitutes all disregarded values in the vicinity of a given support node.