Nonlinear Aggregate Interlock

The nonlinear aggregate interlock option in EverFE relies on a two-phase model of the concrete developed by Walraven that is used to develop the basic constitutive relationship across the joint. With this model, the change in aggregate interlock joint load transfer that occurs with changes in joint opening and load level can be captured. To use the nonlinear aggregate interlock model, select the Nonlinear Model option checkbox at the top of the Interlock input panel. The panel will then appear as shown in Figure 1:

Figure 1: Nonlinear Aggregate Interlock Panel

Note that the model name defaults to hard. There are three models installed with EverFE: hard, medium, and soft, each corresponding to different sets of parameters. To use any one of these three models, simply choose from the drop-down list. To create a new constitutive model, click the Create Nonlinear Model button at the bottom of the panel. This will change the Interlock input panel to appear as shown below in Figure 2:

Figure 2: Nonlinear Aggregate Interlock Model Creation

Now, the parameters of the model are in entry boxes that allow their values to be specified. After modifying the parameters and typing a name for the model ("new" in Figure 2), click on the OK button. See the file "user_manual.pdf" in the "documentation" subdirectory for more information on these parameters and the nonlinear aggregate interlock model. This will execute a separate program, which can take between a few seconds and a minute or so to run depending on the speed of your computer. After the program has finished, the input panel will revert back to its original state (Figure 1), with your newly created model selected as current. Your model is now saved on your computer's hard drive, and you can simply select it from the list of available nonlinear aggregate interlock models for future finite-element simulations.

To illustrate the effect of the nonlinear aggregate interlock model, consider a simple two-slab (one row, two column) model with a 250 mm thick slab (E = 28,000 MPa, nu = 0.20, density = 0) founded directly on a dense liquid with k = 0.03 MPa/mm. This is the same example used to illustrate linear aggregate interlock, except that the medium nonlinear aggregate interlock model installed with EverFE is used at the undoweled transverse joint. The model is subjected to an 80 kN axle located at the joint face as shown in Figure 3 below. Each slab is meshed with 12x12x2 elements. Table 1 illustrates the effect of varying the joint opening on displacement load transfer efficiency computed at each wheel location, 900 mm off the longitudinal model centerline. Once the joint opening reaches 4.7 mm, there is no shear transferred across the joint.

Figure 3: Nonlinear Aggregate Interlock Example

Table 1: Effect of Joint Opening on Load Transfer Efficiency

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