This 46 minute lesson starts with the creation of a quick site model with the Mesh tool, as in the introductory lesson of this module.
The external datum point reference elevation (Sea Level, in this case; but the principle applies to the Australian Height Datum AHD or other standard references) is set in the Options menu > Project Preferences > Levels and Project North based on its relationship to the elevation of the lowest story. Project Zero remains identical to the lowest story elevation, although it is possible to set it to another value if desired.
When creating the site mesh, it’s generally best to create it with the top height just below the lowest point of the site, and a minimal thickness (such as the default 3′ or 1m). Draw the mesh using only the main boundary points, and set the elevation of each one properly, then check in 3D to verify that the prevailing grade is correct and that you haven’t missed any of the points, and that they all have been set properly.
To minimize polygons (and thus the work by ArchiCAD to view or cut sections through the site mesh) you may want to create curved edges using straight segments. This is optional but may be particularly useful when a large or complex site is being modeled.
To create topographic contour lines, select the mesh and make sure the Mesh tool is active in the Toolbox. Click inside the mesh to start the contour, and keep clicking to define the topo line. You may terminate the line by double-clicking a point within the mesh, on its boundary, or outside the mesh (the line will get cut off at the intersection of the last line segment and the boundary). Press down on any of the points in that contour line, choose the Set Z-level option in the Pet Palette, and make sure to Apply to All so that all points in that group (the contour line that you just created) are set at the same height.
You may add individual grading points to the mesh without a contour line by starting the same way (with the mesh selected and the Mesh tool active, clicking inside the mesh) then clicking a second time on the individual point. After this point is created, you may press down on it and choose the Set Z-level option to set its height individually.
To annotate the site with Level Dimensions, make sure you activate the Gravity option in the Toolbar to Gravitate to Mesh. Click anywhere inside the mesh to place a dimension reference; if you click on a contour line you should get an exact value, whereas anywhere else you will get the interpolated value of the mesh surface.
The Level Dimensions will initially refer to the elevation as it relates to Project Zero. If you want to have these points refer to the external datum (such as Sea Level), you’ll need to select the actual Dimension Text element (not the bullseye marker for the dimension) and edit the displayed value to be Custom Text in the Info Box. Once you choose Custom Text, use the small popup menu to insert a reference to the desired datum point (clearing the original reference to Project Zero).
Unfortunately, there is no way to set the Level Dimensions to default to displaying Sea Level or external datum references, so one has to “fix” this after placing the dimension elements. To do this quickly, select all Level Dimensions, then Shift-click to select ONE of the Level Dimension Text elements, and make the adjustment as above. All of the selected Level Dimensions will have their Text elements affected.
To regrade a site, one may create a copy of the original mesh and put it on a separate layer. You may then move contour lines around or add additional contours or individual point references. You may also use Solid Element Operations (SEO) to clear a space for the building slab and foundations (use Subtraction with Upward Extrusion to remove the volume of the slab plus all the air space above it).
It is easy to calculate cut and fill volumes by using SEO between the original and new mesh elements. As a starting point reference, the original volume of the terrain may be viewed using the Window menu > Palettes > Element Information palette.
To calculate the volume of material that needs to be Cut from the original terrain, simply use SEO to subtract the new mesh from the original mesh. To get the Fill volume, use SEO to subtract the original mesh from the new one. In either case, the modified elements may be viewed in 3D to see the volumes cut or filled. It may be desirable to set the materials for each mesh to different colors for clarity of presentation.
To retain the Cut or Fill volume element for reference or inclusion in an Interactive Schedule, a series of four separate Mesh elements is required: one for the original terrain, one for the final terrain, and one extra copy of each that is used with SEO to model and calculate either the Fill or the Cut volumes.
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