Welcome to CivilGEO Knowledge Base
Welcome to CivilGEO Knowledge Base
Defining Deck Roadway Geometry for HEC-RAS Bridge Modeling
In GeoHECRAS, the Deck Roadway data panel of the Bridge & Culvert Data dialog box provides a table for entering and editing the roadway high chord and bridge opening low chord geometry. The data in the table is used to describe the area that is blocked due to the roadway bridge deck, road embankment, and bridge opening vertical abutments. This data panel is displayed by default when the dialog box is displayed.
Note that there are two tabs at the top of the geometry table that correspond to the upstream and downstream faces of the roadway crossing. The user can copy the current bridge deck and roadway geometry from the upstream cross section to the downstream cross section (or vice versa) by clicking on the [Copy to Downstream Cross Section] button.
The following sections describe how to interact with the Deck Roadway data panel of the Bridge & Culvert Data dialog box.
Roadway Structure Dimensional Specifications
This section is used to define the width, distance, and slope of the road crossing.
The section contains the following entries:
- Distance Between Bounding Cross Sections: This is a read-only field, and it shows the distance between two cross sections located a short distance downstream of the roadway bridge and another located a short distance upstream of the roadway bridge. The bounding cross sections are a crucial aspect of bridge modeling. It provides a means of analyzing the impacts of the bridge structure on the flow.
- Roadway Width (Parallel to Flow): The Roadway width (parallel to flow) entry field is used to enter the width of the roadway crossing along the stream. Alternatively, the user can click the [Pick] button to measure roadway width parallel to flow from the Map View.
- Distance from Railing to Upstream XS: The Distance from railing to upstream XS entry field is used to enter the distance between the upstream side of the roadway and the cross section immediately upstream of the roadway. Alternatively, the user can click the [Pick] button to measure the distance from the Map View
- Upstream Embankment Side Slope (V:H): The Upstream embankment side slope (V:H) entry field is used to enter the slope of the road embankment on the upstream side of the roadway. The slope should be entered as the horizontal to vertical distance ratio of the roadway crossing.
- Downstream Embankment Side Slope (V:H): The Downstream embankment side slope (V:H) entry field is used to enter the slope of the road embankment on the downstream side of the roadway. The slope should be entered as the horizontal to vertical distance ratio of the roadway crossing.
Roadway Weir Overflow Specifications
This section is used to define the minimum weir elevation, maximum submergence ratio, weir crest shape, and weir coefficient for an overflow weir on a roadway.
The section contains the following entries:
- Minimum Weir Elevation (optional): The Minimum weir elevation (optional) entry field allows the user to enter the minimum elevation for which weir flow will begin to be evaluated. If this field is left blank, the elevation that triggers weir flow is based on the lowest high chord elevation on the upstream side of the roadway. Alternatively, the user can click the [Pick] button to select elevation from the cross section on the Map View.
- Maximum Submergence Ratio: The Maximum submergence ratio entry field defines the maximum allowable submergence ratio that can occur during weir flow calculations over the roadway. If this ratio is exceeded, the program automatically switches to energy-based calculations instead of pressure and weir flow calculations. By default, the software uses a value of 0.98 (98 percent submerged).
- Weir Crest Shape: The Weir crest shape dropdown combo box entry allows the user to specify weir types. There are two options available: Broad Crested and Ogee. The user can choose the weir type that best matches the problem.
Note that if the user selects the Ogee shaped weir, two additional parameters: Spillway approach height and Design energy head are displayed in the Roadway Weir Overflow Specifications section.
- Spillway Approach Height: The Spillway approach height entry field defines the height, which is equal to the elevation of the spillway crest minus the mean elevation of the ground just upstream of the spillway.
- Design Energy Head: The Design energy head entry field defines the height, which is equal to the energy grade line elevation minus the elevation of the spillway crest.
- Weir Coefficient (Cd): The Weir Coefficient (Cd) entry field allows the user to enter a weir coefficient that will be used in the weir computations. Note that different coefficients may be selected, depending on the use of Metric (SI) or US Units. By default, the software uses a value of 2.6. The user can click on the […] button to display the lookup dialog box containing weir coefficients.
Roadway Crossing Skew
This section is used to define a skew angle for the roadway crossing and bridge piers.
- Roadway and Abutment Skew Angle: If the entered Roadway and abutment skew angle is valid, the software then adjusts the stationing values.
- Bridge Pier Skew Angle: If the entered Bridge pier skew angle is valid, the software then adjusts each pier width entry.
