The user has the ability to apply loads to the model that are custom-defined outside of the EverStressFE environment. This allows the user to create pressure files to define loads that can not be generated within the graphical user interface of EverStressFE. The basic idea is to discretize a spatially varying stress (contact pressure) distribution and generate a list of coordinates with corresponding stress (contact pressure) values that will be used to approximate the distribution. As the number of points used to discretize the stress distribution is increased, the accuracy of the approximation is increased.
The format for these files is relatively straightforward. The file name must contain the extension .node. The first line of the file must contain 4 numeric values separated by spaces or tabs. The first value must be the number of points used to define the pressure distribution, which is also the number of subsequent lines in the file. The second value refers to the dimension and must always be fixed as 2. The third value refers to the number of attributes and must always be fixed as 3. The fourth value refers to the number of boundary markers and must always be fixed as 1. Thus, the first line of a file that contains 5000 pressure points will look like this:
5000 2 3 1
Subsequent lines in the file must contain 7 values. The first value is the point number (starting with 1). The next three values are the x-, y-, and z-coordinates of the point where the pressure is being defined. In EverStressFE, the z-coordinate should be fixed as 0 for loads that are applied to the pavement surface. The next three values in the line are the x, y, and z components of the applied stress [units of MPa (N/mm^2)] at the specified coordinate. In EverStressFE, the x and y components will be 0 for vertical loads applied to the pavement surface. Thus, an input file that contains 5000 pressure points may look like this:
5000 3 2 1
1 100 1000 0 0 0 0.69
2 100 975 0 0 0 0.68
3 100 950 0 0 0 0.66
...
...
4999 500 550 0 0 0 0.36
5000 500 525 0 0 0 0.345
The user may generate a sample file to view the format by clicking on the Loads tab, choosing the User Defined option for Tire Contact, clicking on the Tread Designer option, and clicking on the Save Custom Load button. This .node file will contain 4949 data points, which was found to be sufficient to accurately define all of the nonunifom User Defined pressure distributions that can be created within the EverStressFE interface.