Addition of a Shape to the Program

Addition of a Shape to the Program

Let us say, I need to add some “xyz” shape, I can change the name in the field marked in the figure to xyz

Figure 1: Original name

Figure 2: Modified name

For the time being I have put an equation for square, but you can change it to whatever you want. I will first explain the “Review equation for this shape” program.

After you click “Review equation for this shape” button, you see the following screen:

Figure 2: Modified name

The cells in color have equations for the moment of inertia, centroid, area and perimeter. For example, the highlighted cell with the ellipse has an equation for moment of inertia for a square cross-section. The equation in the cell is written as follows.

=dm^4/12

Note that the variable name in this cell to be used is “dm” as pointed at the end of the row. Similarly, the centroid equation is “=dm/2”, the moment of inertia in second row is “=d^4/12”, area in last row as “=md^2” and finally the perimeter in the last highlighted cell in last row is “=4*md”. In case we want to change the equation, we can do it here in the respective cells.

Similarly, if we want to start fresh i.e. all these cells with nothing in it to confuse us, we can click the “Enter equation for this shape” button in the input sheet. It will take us to the same sheet in figure 1 but with no equations in it (figure 3). We can input any kind of equation with any power etc. The only constraint in the input for the equation is that they should be in terms of a single variable and finally the variables should be named as pointed out in respective rows.

For an example, if you want to input the equation for a rectangle which has the equation for moment of inertia as bh3/12 and you know that the height to width ratio is say 1.5 (i.e. h/b = 1.5 or h = 1.5*b). We can write the equation as:

I = bh3/12

= b*(1.5*b)3/12

= 1.53*b4/12

Figure 2: Modified name

Therefore, we can write the first equation in excel as “=1.5^3*dm^4/12”. Note that the term “b” has been replaced with “dm” since the first cell should have the variable as “dm”.

Once we are done entering/modifying these equation, click the “Go Back to Input Sheet” button to get back to the input sheet to continue with the analysis.