HMA thickness It was suggested that the HMA layer should have a minimum of 2.5 to 3 in after milling as recommended by Speakman (1996) and Cown (1993). During the development of the PCA stress prediction equation using 3-D FE, the HMA thickness was assumed to be 3 or 6 in. The range was assumed to be 3 to 9 in when developing the stress prediction equation using 2-D FE. In the design example, a thickness of 5 in was used for the HMA. Joint spacing Based on the field data, it was concluded that the maximum joint spacing of 4 ft should be used. Square concrete slabs of 2 ft and 4 ft were used in the development of the PCA structural models (both 2-D and 3-D models). In the design example, a joint spacing of 4 ft was used. Environmental conditions Temperature differences were used to calculate the thermal stresses. Based on the temperature °F, measurements made in Colorado and Missouri, three temperature differences in the slab, +15 +5 °F, and -10 °F, were used for stress computations. No guidance was provided to determine this input for design. Structural model A structural model was proposed to predict the pavement response under traffic and temperature loads. First, a whitetopping pavement structure was modeled using 3-D FE method to calculate the stress at the top of the PCC layer and strain at the bottom of the HMA layer. In an effort to reduce the computational expense associated with 3-D FE analysis, 2-D FE analysis was then carried out to establish correlations between the 2-D and 3-D FE calculated stresses based on a multiple linear regression of the cases presented in . The flowchart in illustrates how the model was developed.
HMA thickness It was suggested that the HMA layer should have a minimum of 2.5 to 3 in after milling as recommended by Speakman (1996) and Cown (1993). During the development of the PCA stress prediction equation using 3-D FE, the HMA thickness was assumed to be 3 or 6 in. The range was assumed to be 3 to 9 in when developing the stress prediction equation using 2-D FE. In the design example, a thickness of 5 in was used for the HMA. Joint spacing Based on the field data, it was concluded that the maximum joint spacing of 4 ft should be used. Square concrete slabs of 2 ft and 4 ft were used in the development of the PCA structural models (both 2-D and 3-D models). In the design example, a joint spacing of 4 ft was used. Environmental conditions Temperature differences were used to calculate the thermal stresses. Based on the temperature measurements made in Colorado and Missouri, three temperature differences in the slab, +15 °F, +5 °F, and -10 °F, were used for stress computations. No guidance was provided to determine this input for design. Structural model A structural model was proposed to predict the pavement response under traffic and temperature loads. First, a whitetopping pavement structure was modeled using 3-D FE method to calculate the stress at the top of the PCC layer and strain at the bottom of the HMA layer. In an effort to reduce the computational expense associated with 3-D FE analysis, 2-D FE analysis was then carried out to establish correlations between the 2-D and 3-D FE calculated stresses based on a multiple linear regression of the cases presented in . The flowchart in illustrates how the model was developed.