Create Negative Extrusions

Structural Design User Guide

Create Panels : Create Negative Extrusions

A negative extrusion is created in exactly the same way that the user would position Panel Vertex elements to define the shape of a 2D Panel Loop and then extrude this by the required thickness to create a 3D Panel.

The user can also position Vertex (VERT) elements to form a 2D Loop (LOOP) and then extrude this to create a 3D Negative Extrusion (NXTR). The difference is that, as its name implies, the negative extrusion represents a negative volume, that is, a hole.

A negative extrusion is owned by the panel through which the hole is required. When created, its justification is set automatically to be the same as that of its owning panel, although it can be moved later if necessary.

Here this facility is used to create a hole through the floor plate where one of the columns passes through it.

Vertices V1-V4 in this diagram define the negative extrusion; their numbering is independent of the panel vertices.

Note:

Negative extrusion vertices are shown in italic to distinguish them from panel vertices.

Notice how the outer edge of the negative extrusion (V1-V2) extends beyond the outer edge of the panel to make sure that the hole always penetrates through the panel edge. Similarly, the thickness of the negative extrusion should exceed the thickness of the panel to make sure that the hole always penetrates completely through the panel.

To create a negative extrusion where a column passes through the midpoint of the edge of a panel, navigate to that panel.

On the Plates tab, in the Create group, click Panels, select Negative Extrusion from the list to display the Create Negative Extrusion window.

To see the negative extrusion volume in the 3D view, select Settings > Graphics > Representation and clear the Holes Drawn check box. Select Apply and OK the change.

To achieve the correct justification and orientation for the negative extrusion relative to its owning panel, from the Settings pane of the window, click Surface. Then pick the upper face of the panel.

Note:

To get a better view, zoom in close to the panel and the column of interest and look along (and slightly above) the panel.

The hole penetrates into the panel thickness from this surface.

Set Hole Depth (equivalent to the thickness of the negative extrusion) to 250. A large depth like this makes it easy to see the volume of the negative extrusion once created. A depth slightly greater than the panel thickness would normally suffice, since the application automatically adds 1mm to make sure that the hole always cuts through the referenced panel surface. The settings pane of the Create Negative Extrusion window is populated as shown:

Use any combination of the methods used to create and modify panel vertices (see and Measure Distances/Directions in the Design Model). The user now creates the four vertices needed to define the required hole round the column, as shown in the diagram. For ease of positioning, align V1 and V2 with the outer face of the column (although any position beyond the panel edge would be satisfactory).

When the four vertices are created, click OK.

The Create Negative Extrusion window is dismissed and the Loop Vertex Editor window is displayed.

When created, the negative extrusion appears as an outline volume superimposed on the design in the graphical view. If positioned correctly, its upper face just protrudes from the top face of the panel, as shown:

(If not, use the Position > Relatively (BY) menu option to move the negative extrusion vertically to a position where it cuts both faces of the panel.)

To see the result of applying the negative volume represented by the negative extrusion to the positive volume of the panel, revert to Holes Drawn On representation. The negative extrusion creates a hole only through its owning panel; it does not affect the column.