A strut-and-tie model is easier to understand
if a drawing is shown in the background. But background drawings do
have an additional function; they can simplify the input of the nodes
of the model. When you create new nodes, you can snap to background
points, end of lines, intersection of lines, etc.
For the creation of the drawing, a CAD-program is required.
Lines (Line,
Polyline, LwPolyline), points, circles and arcs will be drawn. Other
entities, i.e. text, solids and so called inserts, will be ignored.
Any format information, like line thickness or colour will be ignored
as well. The original file will not be modified.
If you don't have a CAD-program, you can create the drawings in a simple text editor. Save it with the ending bgd. Example:
# Example for a drawing, created in a text editor
Points
0 6 // x- und z-coordinates of the point
4 2
4 6
9 2
13 0 2 // Input in format x y z is allowed, Fachwerk just reads reads the x- und the z-values.
13 6
Line // This line joins two points
9 2
13 2
Line // If there are more than two points, the line goes through all of them, from the first to the last.
0, 6
4; 2
9,2
Circle
5 5 // center
2 // radius
Arc
13 6 // center
2 270 0 // radius, starting-, end-angle (anticlockwise)
The numbers of one
row may be separated by white spaces, tabulator or a comma. Comments
start with // or # or rem. The sequence of the commands (Point, Line,
...) does not matter: the file may start with lines, followed by
points, then again a line ... Normally, only the leading letter of a
command is required. Commands are not case-sensitive.
In a spreadsheet application you can create a list of points and save it as a csv – file. Fachwerk can display these points in the background. This way, new nodes can be created fast, just snap to the points.