Transition Curves (for Railway Cant)

[Anonymous]

I have attached a screenshot of my problem, and supplementary files if necessary to look at in more detail. This is a student project.

Description: I am working on a rail project with a track spacing of 1.22m, which is different from pretty much every standard out there. So I have fiddled the formulas in Civil 3D to take this into consideration, and tested them on a curve with 325m radius, and I've produced an Excel spreadsheet to double-check the values and tolerances.

The problem: the length of the transition curve in the Excel spreadsheet is 51m. The length of the transition curve in my Civil 3D project is 50m. All the other values are practically identical.

I do not understand the reasons for this disparity. Although it's only a 2% error... it's not really acceptable in rail design. Any suggestions as to what might be the cause for this difference are welcome.

Also... are there any tutorials (video or otherwise) which people here might recommend for learning how to use all of the cant/calculation features in Civil 3D for rail? I've looked and looked, and found very few. I only barely have managed to understand how features such as "Design Criteria" work, or what "Attainment method" actually means, and how the different options are actually different from one another.

[Jowennl]

Hi John,

Thanks for posting your sample rail data and excel calcs.

Comments:

1) I normally see rail alignments with lines, curves, and spirals. (I will show sample in my animated gif below) 

2) In your sample drawing I can only see lines and curves.

3) I assume TL = Transition Length (Is this suppose to be your Spiral?)

Based on your excel you manage to calculate TL and it is so close to the one calculated by Civil 3D. In real world scenario I will go with your calculations as you have used a proper design formula (I assume). I personally think you need to amend your alignment based on your calculated TL. I tried to play around with your drawings and manage to amend the alignment to show sample 2 curves in your calculated TL. (Curve 1 and 4)

Please see attached animated gif. (TestRailCant.gif) 

<Disclaimer>

I'm not a rail designer or expert in rail. I'm just trying to view and experiment with your drawing. I'm just curious.

Cheers,

Jowenn

[Anonymous]

Thanks for your help. That must have taken a fair amount of time to give such a detailed answer.

1) I wasn't sure why the transition curves weren't included in my alignment. That was going to be my next question. As I've been unable to find any tutorials online (even on Lynda.com) that go into the details of adding transition curves for railways.

I assumed the transitions would appear by themselves once I specified the design criteria and did the calculations. Is my understanding correct (from your .gif) that I have to add these separately anyway?

[Jowennl · Accepted solution]

Hi John,

After doing the calc in excel and in Civil 3D your alignment don’t show any spiral. In my opinion you need to add them. You need to choose which spiral to use, either pick your calc from excel or value from civil 3d. I would go with your calc as you have a supporting formula to prove you have the needed minimum TL. Also, your spiral is always longer than the civil 3d so picking that one would be better and more conservative. With your question if you will need to amend and add the spiral my answer is yes. The only problem you may encounter is that some part of your alignment is not logical meaning spiral length won’t fit.

Cheers,

Jowenn

[Anonymous]

Thanks. I think that works well.

It still surprises me that all the values in both Civil 3D's cant table, and my calculations in excel, are identical even to 3 significant figures... except for the calculated transition length. But it's probably not important.

[Anonymous]

I was wondering how you managed to generate the table displayed at the beginning of your .gif animation?

I have been trying to do something similar, but I get a message saying no "tags" selected. I've looked around and have not really got a clear idea of how to create tags in Civil 3D for alignments, how to view them, or link them to tables.

[Jowennl]

Hi John,

I did make that alignment table style customized to what I need. If you want to create alignment table. You can create them inside Civil 3D.

Steps:

• In the Settings tab > Alignment > Label Style > (You need to update Line, Curve and Spiral then setup option as Tag Mode or Labels and Tag Modes)
• In the Settings tab > Alignment > Table Style > Segment (Then modify or make your table style here)
• In drawing model space select alignment then in ribbon click Add Labels > click Add Multiple Segment
• In drawing model space select alignment then in ribbon click Add Tables > click Add Segments

 Toolspace - SettingsSample - For Curve

For demo please see attached animated gif (AlignmentSetoutTable.gif) 

You need to play around with the settings to suit what you need. Tag will give you L1, C1 and S1 as numbering and in my sample I just don't like the number and force them to be L, C and S. and make them Tag Mode only so it won't display in my alignment as label and this is just my preference.

Cheers,
Jowenn