Which Vertical Curve?

[kayak]

Sorry but I'm just not understanding the Autodesk explanation for the different types of vertical curves. I just want a basic parobolic curve based on incoming and outgoing tangents and a length. I also want to be able to change those parameters in my profile. Is it best to use a vc that's fixed, floating, or free? If soneone could give me a simple explanation of the difference, I would appreciate it.

[mjfarrell]

JA..just remember that the definitions are essentially backwards...

A FREE curve vertical or horizontal. is one that is FREE to remain tangent should you change the geometry on either side of thee vertical curve

A FLOATING curve is FIXED on one end and can become non-tangent and FLOATING on the other end; in that it my float to remain tangent should you change the tangent on that end.

And a FIXED curve is limited in that it's geometry will not respond to any changes to the geometry attached to either end of the curve.

Or as I tell my students, a FREE curve is the BEST to use unless the curve needs to pass through some point that is FIXED by some feature, and a Floating curve gives you half a chance to have bad geometry.


Note that when one uses FIXED curves be sure to turn on the alerts for violation of the design constraint parameters.

[jpaulsen]

Autodesk's descriptions have always been confusing. Mjfarrell's description above make a lot more sense.

I typically use "Free Vertical Curve (Parameter)" for 99% of the curves I make. You can choose either length or K value as the controlling parameter. The software will hold the parameter you specify when making changes to the tangents. I prefer specifying the length parameter so when I make minor changes to the tangents I don't end up with some oddball length. I just need to check the K values after making any changes.

The "Free Vertical Parabola (PVI Based)" is another good choice. You only have to pick the PVI instead of both tangents and you have a through point option.

[mjfarrell]

JP,

You could stop checking those K values, by setting the profile properties to enble use of Design Criteria. Then you will see the VIOLATION Triangle warning you that you have stepped out of the design boundary.