Linear Aggregate Interlock Model
Selecting the linear aggregate interlock model requires that you specify a single value for the parameter Joint stiffness that applies for each transverse joint in the finite-element model. The units of Joint stiffness are stiffness/area (MPa/mm or kips/in3), similar to a dense liquid foundation stiffness (k-value). In addition, you must specify a separate joint opening for each transverse joint in the model (Opening between Column 1 and Column 2; Opening between Column 2 and Column 3). Figure 1 below shows the Interlock panel when the linear option is specified for model with three columns of slabs.
The joint opening has no effect on the aggregate interlock load transfer when the linear option is specified. However, small joint openings increase the likelihood of contact occurring between the vertical joint faces, especially if thermal gradients are considered in the model. The joint opening is specified in the aggregate interlock panel since it does have a dramatic effect on aggregate interlock load transfer when the nonlinear aggregate interlock model is used.
Figure 1: Linear Aggregate Interlock Option Input Data
The Joint stiffness is mobilized by relative vertical displacements of two slabs at the joint. A very large value will result in near-perfect load transfer efficiency, while a very small value will produce very low load transfer efficiency. To illustrate, consider a simple two-slab (one row, two column) model with a 250 mm thick slab (E = 28000 MPa, nu = 0.20, density = 0) founded directly on a dense liquid with k = 0.03 MPa/mm. The joint is undoweled, and the model is subjected to an 80 kN axle located at the joint face as shown in Figure 2 below. Each slab is meshed with 12x12x2 elements. Table 1 illustrates the effect of varying the Joint stiffness on displacement load transfer efficiency computed at each wheel location, 900 mm off the longitudinal model centerline.
Figure 2: Linear Aggregate Interlock Example
Table 1: Effect of Joint Stiffness on Load Transfer Efficiency
| Joint Stiffness (MPa/mm) | Loaded Slab Displacement (mm) | Unloaded Slab Displacement (mm) | Load Transfer Efficiency (%) | Max. Stress (MPa) |
| 0.0 | 0.974 | 0.000 | 0.0 | 1.42 |
| 0.02 | 0.828 | 0.147 | 17.8 | 1.40 |
| 0.05 | 0.724 | 0.250 | 34.5 | 1.38 |
| 0.1 | 0.647 | 0.328 | 50.7 | 1.36 |
| 0.2 | 0.587 | 0.387 | 65.9 | 1.34 |
| 0.5 | 0.538 | 0.436 | 81.0 | 1.29 |
| 1.0 | 0.518 | 0.456 | 88.0 | 1.24 |
| 2.0 | 0.506 | 0.468 | 92.5 | 1.17 |
| 10 | 0.493 | 0.481 | 97.6 | 1.00 |