AutoCAD Civil 3D General Discussion

AutoCAD Civil 3D General Discussion

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The association between design speed (V) and radius of circular curve (R),

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08-01-2013 11:25 PM

The association between design speed (V) and radius of circular curve (R),

 

As the R is positively related to V according to the equation (attached), then I expect that the C3D changes R value as the value of V is changed.

 

For example, on the attached screenshots, the R value of horizontal alignment is built based on a design speed of 100km/hr. Now if the speed is changed to 50km/hr, then why the value of R is not automatically changed to be compatible with the new speed?

 

 

Thank you

 

Best

 

Jamal

----------------------------------------------------------
Jamal NUMAN, GIS and Civil Engineer, MSc
e-mail: JamaL9722060@yahoo.com
P.O.Box: 731, Ramallah, West Bank, Palestine.
----------------------------------------------------------
Software: AutoCAD 2014, AutoCAD C3D, AutoCAD M3D, Revit
Windows 7 (Ultimate 64 bits),
Firefox 20.0,
Kaspersky 2013.

Perhaps you did not understand my last post. C3D does not take V into account when laying out alignments. V is only used when using criteria-based design to flag horizontal curves with a radius too small or vertical curves with insufficient K values to the user can fix them.

 

It might be possible for a third party developer to build a utility that would check the horizontal and vertical alignment against the design criteria, and change things where possible to fit the design speed.  You may want to post this request in the Customization forum and see if anyone can help you.

 

Personally I don't want the software making changes like that on its own.  I can see the error flags and make my own judgement about how to fix them.

 

Steve
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Re: The association between design speed (V) and radius of circular curve (R),

08-02-2013 07:53 AM in reply to: JamaL9722060

Perhaps you did not understand my last post. C3D does not take V into account when laying out alignments. V is only used when using criteria-based design to flag horizontal curves with a radius too small or vertical curves with insufficient K values to the user can fix them.

 

Eric Collins, P.Tech.(Eng.)

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Re: The association between design speed (V) and radius of circular curve (R),

08-02-2013 08:10 AM in reply to: ericcollins6932

It might be possible for a third party developer to build a utility that would check the horizontal and vertical alignment against the design criteria, and change things where possible to fit the design speed.  You may want to post this request in the Customization forum and see if anyone can help you.

 

Personally I don't want the software making changes like that on its own.  I can see the error flags and make my own judgement about how to fix them.

 

Steve
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Re: The association between design speed (V) and radius of circular curve (R),

08-02-2013 08:34 AM in reply to: JamaL9722060
Also, a curve designed for 100 km/hr would be perfectly suitable for 50 km/hr. The last thing I would want a program to do is to automatically make all my curves the minimum required radius for a given design speed.

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Re: The association between design speed (V) and radius of circular curve (R),

08-02-2013 08:39 AM in reply to: pinwards

 

Many thanks Eric and Steve. Now it is much clearer.

 

I share the idea of “pinwards” to be able to have the minimum value of R that satisfies the design speed instead of just flagging.

 

Best

 

Jamal

----------------------------------------------------------
Jamal NUMAN, GIS and Civil Engineer, MSc
e-mail: JamaL9722060@yahoo.com
P.O.Box: 731, Ramallah, West Bank, Palestine.
----------------------------------------------------------
Software: AutoCAD 2014, AutoCAD C3D, AutoCAD M3D, Revit
Windows 7 (Ultimate 64 bits),
Firefox 20.0,
Kaspersky 2013.
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Re: The association between design speed (V) and radius of circular curve (R),

08-06-2013 06:55 AM in reply to: JamaL9722060
Hi Jamal.
I think you have misunderstood what pinwards is saying. When he says "The last thing I would want..." this means "I do not want..."

The reason is that the design of the curve will probably be based on many considerations besides design speed. Existing topography and legal boundary lines will influence where the road can be built. I may want a certain curve 'overdesigned' in that the design is much better than the minimum requirements, and I would not want the program to automatically adjust this curve to the minimum. Another curve may be 'underdesigned' on purpose; it doesn't meet the criteria but the engineer has decided that it is the best possible fit for the situation.

Perhaps a useful tool would be one that allowed the user to adjust the R to the minimum value based on V for each curve, one at a time, as desired by the user.


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Re: The association between design speed (V) and radius of circular curve (R),

08-07-2013 12:54 AM in reply to: troma

Many thanks troma for the help. The answer you have already provided is very useful.

 

I got that the value of R can be calculated from two equations

 

R=1719.74/Da, where Da is the degree of curvature

 

R=V^2/127(e+f), V: speed, e:superelevation, f: friction

 

R to be the maximum of these two values.

----------------------------------------------------------
Jamal NUMAN, GIS and Civil Engineer, MSc
e-mail: JamaL9722060@yahoo.com
P.O.Box: 731, Ramallah, West Bank, Palestine.
----------------------------------------------------------
Software: AutoCAD 2014, AutoCAD C3D, AutoCAD M3D, Revit
Windows 7 (Ultimate 64 bits),
Firefox 20.0,
Kaspersky 2013.
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