This Client Server article is republished in its entirety from 2002 for reference purposes.

By Thomas Taylor, Bentley Civil Engineering Support Consultant; and Jana Miller, Bentley Civil Engineering Marketing Coordinator, Bentley Huntsville, Alabama
10 June 2002

Civil engineers often need to make fast and accurate representations of bridge cross sections. InRoads Bridge and MicroStation V8 offer the tools required to do the job, extracting the cross section from the 3D model.

Bentley's InRoads Bridge and MicroStation V8 provide the tools engineers can use to quickly and easily create an accurate representation of a typical cross section of a bridge. This typical section is used to convey to a bridge contractor the dimensions and elements used in constructing the proposed bridge.

Normally, designers create a typical section and then proceed with design. Instead of typical 2D drafting techniques, this workflow involves extracting a typical section from a 3D model. This method is a by-product of the normal roadway and bridge design workflow.

This article outlines some of these tools by taking you through the basic steps for bridge design using InRoads Bridge. A bridge typical section is extracted from the 3D model using MicroStationV8. The key actions in the workflow are:

• Establish horizontal and vertical alignments using InRoads Bridge.
• Create a template and a roadway definition, using the Roadway Modeler tool to establish the bridge deck elevations and surface model. View the surface models.
• Use InRoads Bridge tools to establish the bridge slab fascia, abutment/pier lines, bearing lines and girder lines. Establish vertical bridge geometry for girders, pedestals and footings.
• Display the three-dimensional bridge objects with InRoads Bridge. Use MicroStation 3D tools to create "smart" solids.
• Use Section Generation tool to create the typical section through the three-dimensional bridge design.

This workflow illustrates how to use InRoads Bridge to model and display the finished surface of the bridge deck. Bridge commands are used to display bridge objects. MicroStation commands are used to complete the 3D bridge objects and create the typical section.

Establish the Centerline/Baseline Geometry

The first step in the bridge workflow is to establish the horizontal and vertical geometry for the proposed roadway (see Figure 1). The horizontal and vertical alignments control the application of the typical section to generate the surface model(s). This baseline geometry also controls the location of the proposed bridge, and all bridge geometry will be based on this baseline alignment.

Figure 1. Establishing the horizontal and vertical geometry.
Open a design file and create or load your InRoads geometry file:

1. Create the horizontal alignment.
2. Create a profile along the centerline.
3. Create a vertical alignment as a "child" of the centerline horizontal alignment.

Create a Template

With the alignments established, the next step is to create templates for the bridge approaches and the bridge itself and to establish a roadway definition (Figure 2). The Roadway Definition tool pulls together the stations and templates, as well as other controls (such as side-slope definition) for producing the roadway model (Figure 3).

Figure 2: Creating templates for the bridge approaches.

1. Create a typical section library and define the roadway and bridge cross-sectional geometry and subgrade layers.
2. Create a new roadway library and roadway definition and add a roadway entry that specifies your roadway template and bridge template start and stop stations.
3. Create the proposed roadway and bridge model using the Roadway Modeler tool.
4. View the bridge surface triangles.
5. Save the geometry, the typical section library, the roadway library and the surfaces created by the modeler run.

Figure 3: Producing the roadway model.

Establishing Bridge Geometry

The next step in the workflow is to design the bridge geometry (Figure 4). InRoads Bridge provides the tools needed to lay out the geometric elements for bridge design. Certain critical bridge elements will be displayed in true three-dimensional space. These elements can then be used as a basis for MicroStation tools to be used in completing a true object model. The basic steps involved in defining the bridge geometry are:

1. Create slab fascia.
2. Create abutment/pier and bearing lines.
3. Create girder lines.
4. Define girder type and create verticals along with haunch and camber.
5. Create substructure definition, including bent cap, pedestal type and footing layout.
6. Use the Extrude Bridge command to display the 3D objects in the .dgn file.

Note: These steps outline the basics for minimal geometric layout of the bridge in typical section creation. They do not represent all steps required for final bridge plans.

Figure 4: Using InRoads Bridge to design the bridge geometry.

Using MicroStation V8 to Create Smart Solids and Generate Section

This section describes the steps involved in defining the remaining objects for the bridge design (Figure 5) and generating the typical section for final detail drafting.

1. Use the bridge pedestal top as a control to extrude a cross section of the bent cap. This cross section is used to create a solid object to represent the bent cap. The 3D Utility tools allow 3D faces to be aligned, which can enable the solid that represents the pedestals to be modeled.
2. Take the footing top outline and define the thickness of the footing using the 3D Construct command.
3. Design the pier geometry in a rotated view and extrude to a solid. Place piers on footings and make modifications to the solids as needed.
4. Optionally, solid objects that represent the components of the substructure can be "merged" using the 3D Modify commands.
5. Establish a cutting plane and extract the section by using the MicroStation utility Generate Section from a Plan View (Figure 6). Identify the bearing line (or any line where the section is to be cut) to create the section output.
6. Output can be placed into a separate DGN file. Rotate the view to represent the elements in an "elevation" view (Figure 7). Now the section is ready for final detail dimensioning.

Figure 5: Defining other necessary objects for the bridge design.

Figure 6: Using the Generate Section from a Plan View utility.

Figure 7: An elevation view of the design.

See Also

Client Server Archive

MicroStation Desktop TechNotes and FAQs

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