Roadway Alignment [SIG]

Roadway alignments on OpenBrIM can be defined in two ways: users can either import an alignment or define it using OpenBrIM objects.

Refer to the below page to import alignment from the LandXML file;

In order to end up with a roadway alignment as required, several parameters should be defined.

When you click on the Roadway Alignment subtitle under the Bridge Geometry title, the columns for Name, Start Station, Start Azimuth, Latitude, and Longitude should be seen.

Start Station (Optional): Start Station is used to define the starting reference station for the bridge.

Start Azimuth (Optional): This parameter defines the orientation of the roadway relative to North. For instance, an azimuth of 0° points towards North.

Latitude (Optional): Latitude can be used to define the geographical characteristics of the start point of the structure/alignment.

Longitude (Optional): Longitude can be used to define the geographical characteristics of the start point of the structure/alignment.

1. The Latitude and Longitude parameters can be 0 only if both of the following conditions are met:

   • A geographic coordinate system is not required.

   • There is only one alignment defined in the project.

2. The Latitude and Longitude parameters must not be 0 if:

   • A geographic coordinate system needs to be utilized.

   • More than one alignment is defined in the project.

After making the required definitions, further definitions for Roadway Alignment must be made. When you click on Start Station column’s cell, then appearing three dots, it will lead to options that can be used to further define the related parameter.

For the case of Roadway Alignment:

1. Enter data in the Start Station cell.

2. Click on the appearing three dots.

3. Use the option "Editor…".

4. By using the window, alignment can be defined in horizontal, vertical, and transverse directions.

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Horizontal Alignment Segments

The horizontal alignment of a bridge refers to its plan view or its projection onto a horizontal plane. This involves determining the curvature and direction of the road to create a smooth, efficient, and safe path of travel. The curvature of the road is typically defined by a series of circular curves, or sometimes spiral curves, that connect tangent segments of the road. The radius and length of these curves are determined by factors such as the speed and design vehicle characteristics, the terrain, and the sight distance requirements.

Straight Segments: The supported parameters used to define straight segments on a horizontal alignment are as follows:

• Length​: The length of the straight segment.

Circular Segments: Circular segments are utilized in road and railway alignments to define a curved segment that creates a circular curve section in the horizontal alignment. Following parameters are supported:

• Length​: The length of the curved segment.

• Radius​: Radius of the circular curve.

• Direction​: The Direction parameter specifies the curve direction, with valid options being LEFT or RIGHT, and is determined by standing at the start of the circular segment and looking up station.

Spiral(Transition) Segments: Alignment spiral segments refer to a type of curved segment used in road and railway alignments. Spiral segments are used to transition smoothly between tangent segments and circular curves in the horizontal alignment. They consist of a variable radius curve that gradually changes from a tangent to a circular curve or vice versa. Requires the following parameters:

• Length​: The length of the transition segment.

• Direction​: The Direction parameter specifies the curve direction, with valid options being LEFT or RIGHT, and is determined by standing at the start of the circular segment and looking up station.

• Radius @ Start​: The radius at the start of the transition curve. This parameter is only required if the object is not placed after a Circular object within an alignment.

• Radius @ End​: The radius at the end of the transition curve. This parameter is only required if the object is not placed before a Circular object within an alignment.

Vertical Profile

The vertical alignment of a road refers to its profile or its projection onto a vertical plane. This involves determining the elevation of the roadway at various points along its length to create a smooth and safe vertical path of travel. The vertical alignment is typically defined by a series of grades or slopes that connect the high and low points of the roadway. The slope and length of these grades are determined by factors such as the terrain, the drainage requirements, and the sight distance requirements. Here are the required parameters for vertical elevation points:

• Station​: The station number on the horizontal alignment line for which the elevation information is provided.

• Elevation​: The elevation at the station.

• Grade[%]​: The grade at the station.

A parabolic or cubic curve is then fitted between these points to establish the vertical profile of the alignment. For the vertical profile computation of the alignment, OpenBrIM doesn't require the point of vertical intersection (PVI) - the point at which two tangents intersect. Users can specify the vertical profile by entering the PVC (Point of Vertical Curve), PVT (Point of Vertical Tangency), and grade values at those stations.

Transverse (Superelevation)

Bridge superelevation is a technique used in the design of bridge decks to provide a horizontal curve that matches the curvature of the bridge's roadway alignment. This technique involves tilting the bridge deck slightly towards the inside of the curve, which creates a "banked" effect that helps to counteract the centrifugal force experienced by vehicles travelling on the bridge. The amount of superelevation required depends on factors such as the design speed, curvature of the bridge, and the grade of the roadway leading to and from the bridge. The goal of bridge superelevation is to improve the safety and comfort of drivers by minimizing the potential for skidding or sliding during turns, particularly at high speeds.

Users can define superelevation by specifying one or multiple Cross Section definitions as part of the alignment data at various stations.
Here are the required parameters for a Cross Section​ :

• Station​: Station on which the cross-section is defined.

• Left Edge to PGL​: Location of the left edge of the cross-section from the horizontal control line.

When defining a cross-section in OpenBrIM, users need to use a Cross Section object which must contain one or more Cross Section Segments to describe the shape of the roadway at a specific station. The Cross Section Segments should be stacked from the left side when looking up station. This means that the leftmost segment should be specified first, followed by the segment to its right, and so on. Each Cross Section Segment specifies the transverse slope of a section of the roadway and its width. By stacking multiple Cross Section Segments, the user can define a complex cross-section that accurately reflects the roadway shape at a given station. Here are the required parameters for each Cross Section Segment​:

• Slope​[%]: The transverse slope of the segment. Positive for upward slope (going from left to right).

• Width​: The width of the segment.