3.3 Data Input Components
Data input for FPS 21 consists of a Main Menu screen and three pages of inputs. The current screen layout streamlines data input over the older FPS-19W system, but remains very familiar to veteran users of this earlier version.
Project Information inputs (input page 1) will be discussed first; then Basic Design Criteria, Program Controls, and Traffic on page 2; then Construction and Maintenance Date and Detour Design for Overlays on page 3; followed by Design Type and Material Parameters (page 3).
See Table 5-1 for a summary of recommended inputs that will have a direct impact on the designed pavement thickness.
Parameter | Condition | Recommended Value | Comments |
|---|---|---|---|
Initial SI* | Surface Treatment | 3.8 - 4.0 | Using a lower Initial SI has the effect of thickening base. |
Thin/Intermediate ACP (1.5 in. to 4 in.) | 4.2 - 4.5 | Actual ride for new projects is better than historic values. The lower Initial SI has the effect of thickening base. A 3 to 4 in. surface can have two smoothness opportunities. | |
Thick ACP (> 4 in.) | 4.5 - 4.8 | Should be reduced to 4.5 if the minimum serviceability value is set at 2.5 or less. Thicker pavements have multiple opportunities to achieve higher SI values. | |
Minimum SI* | Surface Treatment or <1 M ESALs | 2.0 - 2.5 | Allowing a lower Min. SI has the effect of thinning the pavement structure. Risk is accepted requiring additional maintenance before termination of pavement life. |
Thin/Intermediate ACP (1.5 in. to 4 in.) or Between 1 M and 3 M ESALs | 2.5 - 3.0 | ||
Thick ACP (> 4 in.) Or > 3 M ESALs | 3.0 | ||
Confidence Level | All Design Types | C (95%) | A confidence level of C (95%) is recommended for all levels of traffic loading. Attempting to use lower levels will almost always result in a design that will not meet the Modified Texas Triaxial requirement. Using higher levels will result in an overly conservative design. |
District Temperature Constant | All | 31 | Overwriting the default will cause thicker designs for Districts in colder regions, but will not mitigate thermal cracking potential. |
Swelling Potential, PVR, Swelling Rate | This analysis has been removed from FPS 21. Consider stabilization of the subgrade to address moderate soil volumetric changes due to moisture. Consult Chapter. 3, Section 2, guidelines for more extreme PVR issues. | ||
Overlay Cost | Future Cost | Use current design practice | Review the “Detail Cost” sheet in the FPS output and determine if the overlay cost is driving a design for thicker pavements unnecessarily. The district may wish to consider pavement design selection without overlay cost included. |
Detour (Road User Cost) | Cost for Detour; Non-cash Future Cost | Use the estimated speed through and the appropriate model for the detour | Does not change thickness but may sort design output options based on combined user/construction costs as opposed to least construction cost. |
Cost per CY | All | District-specific cost should be used. | |
* Increased difference between initial SI and minimum SI reduces pavement thickness. | |||