An irregular-shaped footing is divided into strips depending on many factors such as the location of the piers and cutouts, footing thickness etc. These strips are visible on the "Footing Strips" page under Footing Outputs in each orthogonal direction. The page displays the irregular footing's maximum X and Z dimensions, the strip width and length along each direction. The strips are designated by different adjacent colors for easy visualization.
Strip Determination:
The assumptions in determining the strip division along each orthogonal direction are as follows:
1. Any pier or cutout centerline can only belong to one strip in each direction. In other words, the centerline of a pier or a cutout cannot fall on two different strips in the same direction.
2. If the edges joining the vertices of the footing are not orthogonal, a strip containing a partial or full inclined edge is created depending on the location of the piers.
3. The edge of the strip is first determined based on the distance of the footing thickness from the extreme edge of the pier or the cutout. The distance between the pier centerlines is then used to determine the final strip width.
4. Each strip is either a X-direction strip or a Z-direction strip. The X direction strip will always have its effective length as the entire Z direction footing dimension if the strip is rectangular or an average length if the strip is triangular or trapezoidal. Similarly the Z direction strip will always have its effective length as the entire X direction footing dimension if the strip is rectangular or an average length if the strip is triangular or trapezoidal.
5. If the cutout area is less than or equal to 5% of the total footing area, a separate strip to accommodate the cutout is not considered. However if the cutout area exceeds 5% of the total footing area, strips are separated in each direction to account for the cutout.
Recommendation:
1. If the edges of the pier or cutouts fall outside of the strip, it may be best to change the footing thickness or the pier and cutout location such that the entire pier or cutout fall within a strip.
2. In 2019R1 it is not possible to change the strip widths as determined by the program. It may help to manipulate the pier, cutout dimensions and/or footing thickness that may result in desired strip width.
Strip Notation:
The strip designated with a certain notation is displayed on many of the output pages such as Ultimate Soil Analysis, Moments, Reinforcement, Beam Shears.
Example:
X: -5.8478, -3.8999 5.5, 8
The first character represents the axis that the footing is cut into strips. For example, “X:” represents that the footing is cut along the X-axis into these strips.
The 4 numbers represent the rectangle boundary that encapsulates the strip. And those 4 numbers denote:
The first two numbers is the (X,Y) coordinate of the bottom left corner of the rectangle boundary from the centroid of the irregular footing.
The 3rd number is the X-dimension of the rectangle boundary.
The 4th number is the Z-dimension of the rectangle boundary.
Therefore the Example X: -5.8478, -3.8999 5.5, 8:
represents a strip that was cut along the X-axis of the footing, hence it would have the full Z-dimension of the footing. The rectangle boundary of this strip is 5.5 ft in X-dimension and 8 ft in Z-dimension. The bottom left corner of the rectangle boundary is 5.8478 left of the centroid along X-axis and 3.8999 bottom of the centroid along Z-axis.