Survey: Horizontal Curve Problem Need Help!

[Lungshen]

I have been studying cumo, Reza and Mansour's books for the civil survey.

I have found there are a lot of problems - if not all, are identical in Reza's book and Mansour's book.

However, I have found there seemed to be one discrepancy on one of the horizontal curve problems between these two books.

Please keep in mind these two problems are EXACTLY identical in problem statment and numbers.

The problem is involving an easy equation with known External distance (E) and to solve for Radius of curve required.

In Reza's book, chapter 6, problem 16. pg 50 The external distance is taken to be 32' + 8' and when outside Radius is solved, then subtract 25' (half of the road width) to get the centerline Radius of the road. The answer given is 3162.5'

Now, in Mansour's book, Chapeter 10, practice problem 8, pg. 256 the solution given to the problem is, the External distance is taken to be 32'+8'+25'=65', and thus the solved Radius is 5179.60'

It seems two difference approach gives totally two different answers.

Which solution is the CORRECT solution??

For those who have both Reza's and Mansour's books, can you please help shed some light here?

Thanks in advance.

 

[ptatohed]

Can you post the problem so we can work it out?

 

[ptatohed]

Ok, I dug out my old survey stuff. I do not have Mansour's book but I do have an old copy of Mahallati's workbook (2007). I think I found the problem you are referring to. It's #16 page 109 in my book. I worked the problem before I looked at the solution and got the book's answer of B (3,162'). Solve for R given E. E = 32' (PI to tree) + 8' (tree to outside edge of roadway) = 40'. R = -E cos (I/2) / (cos (I/2) - 1) = 3187.44'. Subtract 25' to get the radius at the CL of the roadway. R = 3162.44'. Answer B.

So, without even seeing Mansour's solution, just going by what you said, I know Mahallati is correct and Mansour is wrong. It is not correct to simply add the E of the outside roadway curve to the 1/2-width of the roadway to get E for the roadway CL. The roadway CL does not pass through the BC and EC of the outside edge and is its own curve with its own E.

It's 2am, I hope that made sense.

 

[Lungshen]

Ptatohed, thank you for your prompt reply. You have been a tremendous help to this survey forum.

I was wanting to attach file but couldn't figure out how to do it on this forum...

Yes, the solution from the Mansour's book take E to be 32' + 8' plus another 25' (to the CL of the 50' wide road) So with E = 65', using Eqn. R = E cos (I/2)/(cos(I/2)-1) = 5179.60'

The answers didn't even have 3187.50' as an option. Though Reza's book gives both 3187.50' and 5179.60' as distractor.

I'll take your expert opnion and use the solution from Reza if a similar question appear on the exam.

I am surprised to see that Mansour's book have errors. His survey review book is a very well put together material for someone who is structural has no survey background at all. I can follow his book easily and the the materials are well organized.

Reza's practice book only have practice problems and solutions. I struggled with it but got through all the problems before I started Reza's book. Most of the problems are exactly identical so it kind of help me to refresh my memory when going through Mansour's book.

 

[Lungshen]

here is the solution for the problem.

 

[ptatohed]

I wonder why the two different authors/books share so many similar problems?

I think the problem is in the lack of specific wording in the problem statement. Usually problems like this will ask you to solve for the minimum radius that will work. Or, the problem will usually state that you are to hold the same BC/EC, etc. While one could argue that both methods provide a correct answer, I'm still going to go with Mahallati. If you look at the problem graphic, it seems to me that the radius and tangents shown are for the alignment of the outside roadway (I think?). If you use Mahallati's method, you maintain the tangents as the outside roadway's alignment tangents. If you use Mansour's method, the tangents that were originally shown for the outside roadway edge become the roadway centerline's alignment tangents. Please see the graphic attached.

That's my take anyway. Do you guys agree?

Mansour #8.pdf