Dances with Curves: A Journey into Uncharted Territory for ...aucache.autodesk.com/au2011/sessions/5806/class... · Dances with Curves: A Journey into Uncharted Territory for Interchange

Dances with Curves: A Journey into Uncharted Territory for Interchange Modeling with AutoCAD® Civil 3D® Rad Lazic – Parsons Brinckerhoff

CI5806 Learn how to make the best use of AutoCAD Civil 3D parametric drawing, alignments, and corridor objects for interchange layout and modeling. Experience the simple steps to automation of any interchange layout design. This class will expose in detail the best practices for using combined AutoCAD and Civil 3D features for automating interchange modeling. You will learn how to build libraries of content to increase automation, flexibility, and design quality, and have fun with design and modeling of interchange layouts such as cloverleaf, half-cloverleaf, trumpet, diamond, Maltese cross, or any composite layout.

LearningObjectives

Use best practices with corridor modeling for fun and dynamic evaluation of alternative layouts and models

Use parametric drawing to define constrained curvilinear objects such as loop, indirect, and direct on/off ramps

Describe best practices for automating alignment layouts for interchange design

Develop a library of dynamic objects such as blocks for interchange layouts such as cloverleaf, trumpet, and Maltese cross

AbouttheSpeaker As a BSc, CE, Rad has worked on many transportation infrastructure projects since 1991. Rad has over 15 years of experience providing technical consulting services to users of Autodesk® software. Rad specializes in software implementations for transportation clients. Clients range from major engineering consulting companies to government organizations. His major strengths are in problem solving, initiative, customer service orientation, creativity, oral communications, and flexibility and adaptability. Rad has driven many AutoCAD® Civil 3D® implementation projects to success. Those projects included custom content creation, custom training, and CAD management. [email protected]

Dances with Curves: A Journey into Uncharted Territory for Interchange Modeling with AutoCAD® Civil 3D®

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Let’sDefineitFirst

Have you ever wondered how many times in a day we pass by or drive over a highway interchange? Probably not. Besides a rush-hour traffic or a focus on maintaining a safe speed along those led-foot teaser bends, not much can be seen in terms of interchange layout and shape, even while living in a place surrounded by them.

We need to take 8,000 feet altitude view to see how those ramps and curves are shaping up. I was really having fun while I was interchange hunting on the internet and how easy it is to see different types and layouts more common in some parts of the world than the others. I’ll leave that excitement to you to enjoy in spare time but for this paper, I have singled out just a few examples to set a direction for us.

To start categorizing our topic, let’s divide it in to:

Interchanges with at grade intersections, such as:

With Civil 3D’s automation for intersection layout and grading, there are not many

secrets to modeling those. We will focus on modeling interchanges without at-grade intersections. So, ramps and bridges only, such as:


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Of those types, some of the few standard ones, according to CALTRANS Highway Design Manual are:

Or, “Maltese Cross” layout:

Or, “Cloverleaf” layout:

Or, “Trumpet” layout:

This paper will focus on components and similarities of modeling such interchanges. Endless combinations are possible as derivations of those listed above.


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Let’sbreakitdownintosmallerpiecesDesigning and modeling an interchange will probably be the most complex task to complete. It’s useful to break it down in components. Let’s use a cloverleaf interchange as an example.

It is strongly recommended that the sequence of adding components to the model is followed to avoid reworks and dead ends. Here is one of possible simple workflows for any interchange model:

1. Create Primary/Secondary road corridor models with extended widths (count: 2). Create a temporary TOP surface for grading the ramps.

2. Design Alignments for inner (loop) ramps (count: 4 exits, 4 entries, 4 loops). 3. Design Superelevation for loop ramps alignments (count: 4). 4. Sample EG, Primary and Secondary road TOP surface profiles and design

profiles layouts for Inner (Loop) ramps (count: 4). 5. Create Corridors for loop ramps (count: 4). Define corridor regions. 6. Define corridor regions for Primary and Secondary roads. Assign targets for

widening in ramps exit entry areas. Adjust the TOP surface boundaries. 7. Grade paved gore areas at loop ramps exits and entrances (count: 8).

(extend the ramp in to the region, create an offset alignment over the common region, sample the road TOP surface for it, assign it as the target for the ramp)

8. Adjust the superelevation for the ramp at ends. 9. Direct ramps layout (count: 4 exits, 4 entries, 4 curves) 10. Design superelevation for direct ramps alignments. (count: 4) 11. Loop ramps regions with extended widths (count: 4) 12. Loop ramps TOP surfaces (count: 4) 13. Direct Ramps Profiles and Corridors (count: 4) 14. Define Regions for Direct Ramps (count 4x7=28 approx) 15. Amend regions for Primary/Secondary (count 2x17=34 approx) 16. Model Loop/Direct join areas (count: 4x2=8) 17. Model Loop ramps daylight intersecting areas (count: 4x2=8). Example:

Grading Object. 18. Model Direct ramps daylight intersecting areas (count: 4x2=8). ). Example:

Grading Object. 19. Create TOP surfaces from ramps. 20. Paste TOP surfaces to the final FG. 21. Design bridge layouts. 22. Create Corridor solids for all corridors.


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To pimp up this model, we will need some spare parts:

1. Primary road corridor with TOP surface model.

2. Secondary road corridor with TOP surface model

3. Typical ramps layouts (count: 4 deceleration lane types, 1 acceleration lane type, 1 loop ramp type, 1 direct ramp type)

4. Assemblies (count: 4 primary, 4 secondary, 3 bridge decks, 3 ramps, 2 "curb" returns.

TheLayoutEvery interchange begins with a Primary and a Secondary road crossing and the decision to separate them in space for continuous and safer traffic flow. The layout and models of intersecting roads are usually pre-defined.

Someone said that a curve proves that any straight section of the road that precedes it, was leading in a wrong direction. An interchange is a place where we have two choices to change the direction of driving and take a right or a left turn. So, what makes up an interchange is a set of connecting roads or ramps for each possible turn. Typically, there are up to eight ramps to support those turns.

If you pay attention to different shades or colors on the previous page, you should begin to see a pattern. We can break any interchange in to connecting ramps and recognize the following common types of ramps:

Loop Ramp (orange in the layout) - left turn, more than 180 degrees (270d) - minimum radius = the slowest drive - the greatest elevation difference

Direct Ramp (magenta in the layout): - right turn, around 90 degrees - large radius = the fastest drive - the lowest elevation difference

Indirect Ramp (blue in the layout): - Left or right turn 90 – 180 degrees - Changing radius = variable speed - Changing elevations, often on a bridge


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It’s not hard to see that a cloverleaf interchange is held together by four loop ramps and four direct ramps. “Maltese Cross” has four indirect ramps and four direct ramps. Trumpet has a loop, indirect and two direct ramps. We could compile pretty much any interchange layout by using those three types of ramps.

For this workflow, I have developed a library of typical ramp Alignment objects and saved them as blocks. We can build a tool palette from those blocks. When you insert one of those blocks and explode it, the alignment packaged inside the block will be added to the Prospector tree, with any profile Layouts designed for that alignment.

Here is an example of trumpet interchange put together from those ramp layout blocks:


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Useful tools at this stage of are “Create Alignment From Existing Alignment” where you can copy a part of an alignment in to the new one.

We can bring the additional entities by converting AutoCAD line or arc:

Pay attention to the direction of Arrow it has to point in the direction of the whole alignment. Use Reverse sub-entity button to correct if required (the next button on the right).

Or, we can use one of the many entities with geometric constraints from the tangent, curve and spiral menus. Geometric constraints are very useful for respecting the local bounding conditions while parameter editing or grip editing the ramps sub-entities. The set of pre-defined ramp alignments was created with the most common/most flexible set of geometric constraints.


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For more details about geometric constrains, refer other classes that focus on the subject or to Civil 3D help files.

In some cases, we can drop in the whole interchange layout from the block saved on tool palette:

This may save a lot of time with initial layout of typical interchanges.


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GradingtheinterchangeThe next step is to develop series of corridor objects, one for each ramp. This will require a library of Assemblies, carefully crafted to support all cases of joining and targeting components. Something very similar to Intersection Assembly sets only, this one will be developed and maintained by you.

A good example is to have variations of Primary and Secondary roadway assemblies and the same goes for the ramps. Again, the Subassembly set can be saved on the Tool Palette and, you don’t have to create blocks from them:

The first step is to define Superelevation for all ramps. Use the automated method but be prepared to edit and replace with manual entries in the areas where ramps detach/attach to the connecting roads or other ramps. Superelevation Tabular Editor will play the major role for this


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step:

We may have to go back to this tabular editor later, to adjust details.

To add detail to grading, you will have to manage all corridor properties. Use functions from the Corridor Modify tab to access corridor properties directly. This will speed up the process:


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To treat areas of converging ramps, create a Feature Line from ETW of one corridor. Have an added, 1’ lane and target the Feature line for both width and elevations.

To define the area between two corridors where the Daylight slopes from adjacent lanes intersect with each other before they intersect with existing ground, draw a Feature line around the region, connecting the ends of Unpaved Shoulders. The adjacent region’s Daylight links will give the clue about the required extents of the Feature line.

Use Grading Tools to grade the feature line to Surface (EG) at given slope (3:1). The Grading Object will resolve the intersecting Daylight slopes where they overlap and grade to the target surface where they don’t overlap. It will also delineate where one condition stops and the other condition starts.


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PuttingitalltogetherWith Civil 3D, merging parts of the overall model is fun with Surface Edit “Paste” command:


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Forfurtherexploration

We can further enhance the model and perform various types of analysis, such as clash detection between roadways and structures by developing a custom subassembly with the Subassembly Composer. This, application allows engineers and designers to develop subassemblies, roadway elements with specific behavior and logic built in:

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Dances with Curves: A Journey into Uncharted Territory for ...aucache.autodesk.com/au2011/sessions/5806/class... · Dances with Curves: A Journey into Uncharted Territory for Interchange