Interface - Analysis and Design
MPADD2 uses the assumption of uniform flow to calculate the spread at a given curbed section. In accordance with the recommendations in HEC-12, the program uses a default value of 0.3% for the profile grade when the input data results in a grade of 0.3% or flatter. This approximation provides a reasonable solution for the design of most pavement inlets since:
- the critical point in a sag vertical curve is often near the point where the profile grade is 0.3%, and
- a special routine is provided for the design of pavement sumps which normally is accomplished with a safety factor to account for possible partial clogging of the sump inlets. This should provide for a conservative estimate of the spread of the gutter flow in the sump area.
For bridges on flat slopes, the MPADD2 program uses the special flat bridge design algorithm presented in the HEC-21 Hydraulic Engineering Circular on Bridge Deck Drainage. Therefore to extend the ability of the program to include the flat bridge case, two methodologies are presented to the user:
- In the [Run] menu, select [Run|Pavement or Normal Bridge] to analyze a normal pavement or bridge design. In this mode, the program will select a default minimum profile grade of 0.3%.
- Select [Run|Flat Bridge] to analyze or design a flat bridge with slopes of less than 0.3%. Note that this selection should not normally be necessary for bridges on crest vertical curves, since the amount of runoff in this section of the bridge is small and should not exceed the design spread. For flat bridges, it is recommended that both the normal and flat bridge methodologies be run to determine which one governs.
There are three modes for running the program: the batch design mode, the review mode, and the interactive one-by-one design mode. The mode of the program operation is selected by the user in the project input form. For batch design mode and review mode, the program will read the input data and send the results to the output page on the form. For the interactive one-by-one design mode, the program in the mode will ask the user for an inlet location and indicate the results at that location. The program will not proceed to the next inlet until the user approves the location and type of inlet at the station under consideration. This process is repeated until user has confirmed the completion of the design. The results are then either sent to the output page and can be saved as an input file for future use. During the design process, user can change the input data on the input form and get the result from these data. When the desired result is obtained, user can save the input data into the file and print the results.