How to set a value and label the “degree of curvature” for the HA?

[JamaL9722060]

How to set a value and label the “degree of curvature” for the horizontal alignment (HA)?

As the radius of the circular alignment (R) is calculated from the “degree of curvature” (attached) then I couldn’t figure out how to select a particular value for the “degree of curvature” (R=1718.8/Da) and then to label the horizontal alignment with it

Thank you

Best

Jamal

[wfberry]

Jamal:

I am not exactly sure what you are asking.  As you seem to know, knowing either the Radius or the Deg of Curvature will get you what you need.

The easiest thing to do in this case is just make a curve with a certain Radius.  Let the program label the deg of curvature after you have drawn in the curve.

A little more information, please.

Bill

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[JamaL9722060]

Many thanks Bill for the answer,

I got that the radius of circular curve in C3D is calculated from the equation below:

R=1718.87/D, where D is the degree of curvature (in decimal degree).

Then once the degree of curvature is specified by the designer, R can be obtained.

My issue here is that I don’t know where the D is set in the C3D based on which the R is calculated. Also, I couldn’t figure out how to label the curve with this value (degree of curvature).

[wfberry]

Jamal:

I believe we are getting close.  See the attachment.  Go to Settings-> Alignment -> Label Styles -> Curve, Select an object under Curve then follow the picture that I sent.  Also select where it says Curve Group Index on my pic and you can see several items to choose from, two being degree of curve.

Bill

[JamaL9722060]

Many thanks Bill,

Sorry but couldn’t know the degree of curvature (D) based on which the R is calculated (attached). Where this value is managed in the C3D?

Best

Jamal

[wfberry]

Jamal:

As far as I know the only thing that you can enter as a given is the RADIUS (draw the radius when laying out your alignment).  If you want to end up with a certain degree of curve, just divide 1718.87 by your desired degree of curvature, use this Radius and the label should work for the desired degree of curvature.  Since 1718.87 is metric, I am depending on your formula to be accurate.

Bill

[AllenJessup]

OK. You don't lay out a curve in Civil 3D by Degree of Curve. You use the formula and the information you've been given to input he Radius and length. For a label you'd have to create an Expression using the formula.

You have to know if you're using the Arc definition or the Chord definition. In the U.S. the only place you fin the chord definition is on old Railway maps. The Degree of Curve was based on a 100' chord.

The purpose of the degree of curve chord definition was so that when the Surveyors would lay out the centerline of track with a Transit and 100' tape. They could set on the PC, turn the degree of curve as a deflection angle and use the 100' tape to set the next point on the curve. They would then move to that point, backsight the last point and turn the degree of curve angle and go the next 100' chord.

So the Degree of Curve is less a mathematical concept and more a trick used by Surveyors to make the layout easier. Since the Railways were the first long distance design done with precise math. The concepts were carried over to the design of roads. I don't know why the definition was changed to the Arc definition - 100' of arc. I believe the concept was kept because it was useful in calculating curve superelevation and to set minimum radii for curves at a specific design speed.

I've included all this because I find it's sometimes easier to understand something if you know it's origins.

Allen Jessup

[JamaL9722060]

Many thanks Bill and Allen for the very useful elaboration.

I’m attaching in one place the math equations that relate all curve parameters together. From these equations, it sounds that the degree of curvature is data but not calculation. For example, it is recommended that the value of Da must be less than 4 degrees for high-speed highways. That’s, the SMALLER the Da the SMOOTHER the curve and the more COMFORTABLE the circular curve for drivers to pass.

Therefore, the value of R (radius) is dependent on the assumed Da. This is why I expected that the value of Da must be provided for the C3D as an input.

Please, Allen, let me know if you agree with what is mentioned here.

Best

Jamal

[AllenJessup]

Yes. As I mentioned. Degree of curve was held over since it's convenient for specifying/determining the maximum radius for a design speed. However. Since Civil 3D was set up to have the design criteria controlled through a Design Critera file. Autodesk probably didn't think it was necessary to include Deg. of Curve entry.

We often rough out an alignment and then determine the max radius and then add the curves.

Allen

[JamaL9722060]

Many thanks Allen.

Sorry but I couldn’t really figure out how R is calculated and where the value of Da can be modified.

In the attached screenshot, R is provided as 30.67 meter where the given value of R (in the Design criteria editor) is 490 meter.

In most of the academic references that I refer to, the value of R is calculated based on the assumed value of the Da. The value of Da is chosen to ensure comfortable curve for drivers. The smaller the better.

Sounds to be like chicken-egg issue!

Best

Jamal

[AllenJessup]

For the arc definition the formula is (100 [US] or 30 [metric] / Degree of curve = 2 π /360

So Radius = Arc length (100' or 30m) * 360 / 2 π DoC

[JamaL9722060]

Perfect.

Then in order to calculate R, the only thing we need is the value of degree of curvature (Da).

C3D doesn’t allow choosing the Da based on which R is calculated.

How this gab can be overcome? How to set a value for Da based on which R is calculated?

[Matt.Anderson]

The value is found under Alignment Feature Settings > Degree of Curvature > Unit Chord Length and Unit Arc Length.

[JamaL9722060]

Hi Matthew,

In there, one can set the chord length/arc length but not the degree of curvature (attached).

In order to find R, we need to know the chord length/arc length AND degree of curvature (R=1719.74/Da)

Please have a look on the attached file that shows how R is calculated in one of the academic books.

Chord length/arc length are not sufficient to calculate R. We still also need a value for Da

Best

Jamal

[Matt.Anderson]

Jamal -

Its a variable that the user enters rather than input Radius.  For example, this allows the user to add a curve based on DoC between two tangents.

Or use the transparent command CCALC (Curve Calculator) to launch a curve calculator when R is needed and you have DoC (or what ever calculation combination you have)

[AllenJessup]

Thanks Matt,

I've never had to use the degree of curve so I hadn't realized it's an option.

Allen Jessup

[JamaL9722060]

Hi Matthew,

Yes. What I wanted is to have the R calculated based on a given degree of curvature (Da). In this case, the Da should be engaged as an input value to have the R calculated

Arc definition (considering 30 meters arc length):

R=1719.74/Da

Chord definition (considering 30 meters chord length):

R=15/Sin(Da/2)

Waht is the command you used in the screenshot you have already attached?

[Matt.Anderson]

Jamal -

The prompt I highlighted is the commandline input for inserting a curve between two tangents.  It will calculate R based on the manually entered Degree of Curvature and insert a curve with those values.

The Curve-calculator that allows you to select the variables needed to enter, including Degree of Curvature, also solved for R. 

See http://docs.autodesk.com/CIV3D/2014/ENU/index.html?url=filesCUG/topichead_0.htm,topicNumber=CUGd30e1...

[JamaL9722060]

Many thanks Matthew for the prompt help,

Sorry but I couldn’t figure out how to specify the Degree of curvature WHILE drawing the horizontal alignment. The instructions provided in the help are not sufficient to do so.

1. The deflection angle between the two tangents can be provided WHILE drawing the curve by pressing ‘dd (attached)?

1. How the radius (R) is provided WHILE drawing the curve (attached)?