Vertical curves minimum alg. diff.
Vertical curves minimum alg. diff.
(OP)
Hi,
I have heard that a minimum algebraic difference in vertical grades of 0.50 requires no vertical curve to be designed. Is this true? Does anybody know where can I find a reference about this?
Thanks,
Roberttx.
I have heard that a minimum algebraic difference in vertical grades of 0.50 requires no vertical curve to be designed. Is this true? Does anybody know where can I find a reference about this?
Thanks,
Roberttx.





RE: Vertical curves minimum alg. diff.
I believe that this depends upon where your are working. Here in Loveland, CO. they define a maximum algebraic difference befor a curve is needed, not a minimum. As stated in the "Larimer County Urban Area Street Standards" adopted January 2, 2001 in Chapter 7.4.1.B.
2. Grade Breaks:
"No single point grade break shall exceed 0.40 percent."
3. Requirements for Using Vertical Curves:
"Vertical curves are required for grade changes that exceed 1.0 percent. Both centerlines and the curb and gutter flowlines shall be designed with vertical curves to meet the requirements of Standard Drawings 7-17 and 7-18. A series of grade breaks may be used in lieu of a specified vertical curve as long as the series of breaks meet the vertical curve criteria in the Standards for the design speed. K-values for design shall conform to Table 7-3 or Table 7-4.
"In sag curves on flow line, the minimum grade requirement shall override the slope within the vertical curve."
What happens between 0.4% and 1.0%? I don't really know but that's how it's written. Now, aren't you glad you don't work in Larimer County?
Brian
RE: Vertical curves minimum alg. diff.
Thanks for your response, Brian. I am currently working at El Paso, Texas, but I haven't found an AASHTO reference where it actually says that. I would like to count on that because many projects we do rely on it.
I wouldn't hurt if this reference is available no matter what our logic says that that the curve derived from this small difference is going to be a very flat one.
Thanks,
Robert
RE: Vertical curves minimum alg. diff.
RE: Vertical curves minimum alg. diff.
I mostly do street horizontal and vertical alignment design. However, I heard from a teacher that a algebraic difference of more than 0.5% is required to design a vertical curve. Does this apply to highway design? Do you know of a reference about this issue?
Thank you,
Roberttx.
RE: Vertical curves minimum alg. diff.
RE: Vertical curves minimum alg. diff.
Our state (South Carolina) DOT has a design manual that gives min and desirable k values for Stopping SD, Passing SD, and Decision SD. And for drainage purposes a max k = 167 for curbed pavments.
I would love some field experienced person to back this up due to my growing skepticism of handed down practices that don't have the testing behind them. I do have a problem with trust.
RE: Vertical curves minimum alg. diff.
For example if you have an incoming grade of 1% and an outgoing grade of 1.5% and apply a vertical curve of say 20m length, then the resultant shift in elevation at the mid point is only 0.008m above the grade IP. Which is 0.10m above the start point and 0.15m to the end point. In a practical sense a grader operator will not get the accuracy required to construct this given that most tolerances are +-0.010m.
Even if your VC was to be a reasonable length of say 100m then the respective increase in shift of elevation is still relatively small compared to the overall look and would not be noticable. So from a practical point of view it is simply not worth designing a VC for a grade change of 0.50%.
Regards
sc