Vertical Curves Question

[bulls2030]

So I am just making sure, if given the VPI station of a vertical curve and the length of the curve, can we find the VPC station by VPC = VPI +(Length of curve/2)? I am guessing this only applies for symmetric Horizontal Curves.

The reason I ask is because for the attached problem, we are given the VPI station and can find the length of the curve with the givens, but in order to find the VPT, VPT = VPI+Length of Curve-Tangent Length?

Clarification would be appreciated.

View attachment 123.pdf

 

[DuckFlats]

The problem you attached is for a horizontal curve, not vertical. But PVCsta=PVIsta-L/2

 

[bulls2030]

The problem you attached is for a horizontal curve, not vertical. But PVCsta=PVIsta-L/2

Sorry about that lol. been studying all day.

But for this problem, can't you find the PVT : PVT = PVI + Length of curve/2? Why subtract the tangent?

 

[DuckFlats]

That could only work if L was the horizontal distance between PC and PT. L is the actual length on the curve. When you subtract the T from L, you basically are making up for that "extra" distance only L would show. Not sure if that helps, but to be honest, you will probably be fine with the CERM equations. This is my first time taking the test as well, but I am fairly confident they want to make sure we can use the correct equations in a given scenario, not the theory behind the equation.

 

[JonVinci]

I think it comes down to more of a constructibility standpoint. I'm not sure if you work with alignments on your jobs, but you're usually working with stationing along a centerline alignment of your mainline. If you're staking construction details for the contractor, all stationing distances and offsets are from the curve, not along your tangent lines. There's stationing, which is along the mainline, and then there's actual geometrical distances that you compute, which is T.  So to get stationing at your PT, you can ONLY get it correctly by moving along your curve. Which means go backwards from your PVI, then forwards along your curve.

That was a lot of words to tell you always go back words from your PVI to your PVC before going to your PVT. And always use T.

 

[dcald86]

Agreeing with others, always use: 

PC=PI-T

PT=PC+L

 

[bulls2030]

I think it comes down to more of a constructibility standpoint. I'm not sure if you work with alignments on your jobs, but you're usually working with stationing along a centerline alignment of your mainline. If you're staking construction details for the contractor, all stationing distances and offsets are from the curve, not along your tangent lines. There's stationing, which is along the mainline, and then there's actual geometrical distances that you compute, which is T.  So to get stationing at your PT, you can ONLY get it correctly by moving along your curve. Which means go backwards from your PVI, then forwards along your curve.

That was a lot of words to tell you always go back words from your PVI to your PVC before going to your PVT. And always use T.

Agreeing with others, always use: 

PC=PI-T

PT=PC+L

I am working in site development design but I have done some construction staking.

So lets put it this way because I am a bit confused now, For the PE exam, I basically use PC=PI-T and PT=PC+L?

I haven't really had any issues with these types problems until I came across this problem. 

 

[dcald86]

For horiz

I am working in site development design but I have done some construction staking.

So lets put it this way because I am a bit confused now, For the PE exam, I basically use PC=PI-T and PT=PC+L?

I haven't really had any issues with these types problems until I came across this problem. 

For horizontal yes, seems like the topic is jumping back and forth between horizontal and vertical curves.

 

[bulls2030]

For horiz

For horizontal yes, seems like the topic is jumping back and forth between horizontal and vertical curves.

Yea sorry about that. And does the same idea apply for vertical curves as well?

 

[P-E]

I like my curves horizontal. 

Good luck on Friday!

 

[dcald86]

Yea sorry about that. And does the same idea apply for vertical curves as well?

I believe your initial thought is correct for vertical curves

PVC=PVI- (L/2)=PVT-L

PVT=PVI+(L/2)=PVC+L

The V in PVC, PVI, and PVT is for "vertical".  The equations for vertical curves and horizontal curves cannot not be used interchangeably (as vertical curves are parabolic).   Also, stationing for vertical curves is done in a straight line between the PVC and PVT while horizontal curve stationing is done along the curve itself.  Hope this helps.

 

[ptatohed]

I like my curves horizontal. 

Good luck on Friday!

LOL!  Very nice P-E

bulls,

Horizontal Curves:

StaBC = StaPI – T 

StaBC = StaEC - L

StaEC = StaBC + L

Vertical Curves:

StaBVC = StaPVI – (L / 2) 

StaEVC = StaPVI + (L / 2) 

StaEVC = StaBVC + L

 

[bulls2030]

LOL!  Very nice P-E

bulls,

Horizontal Curves:

StaBC = StaPI – T 

StaBC = StaEC - L

StaEC = StaBC + L

Vertical Curves:

StaBVC = StaPVI – (L / 2) 

StaEVC = StaPVI + (L / 2) 

StaEVC = StaBVC + L

Thanks!

This question threw all of the basic curves stuff off for me. Thanks for spelling it out

 

[bulls2030]

LOL!  Very nice P-E

bulls,

Horizontal Curves:

StaBC = StaPI – T 

StaBC = StaEC - L

StaEC = StaBC + L

Vertical Curves:

StaBVC = StaPVI – (L / 2) 

StaEVC = StaPVI + (L / 2) 

StaEVC = StaBVC + L

Just to confirm,

StaBC = StaPI – T       (PC=PI-T)

StaBC = StaEC - L      (PC=PT-L)

StaEC = StaBC + L     (PT=PC+L)

Vertical Curves:

StaBVC = StaPVI – (L / 2)           (PVC=PVI-(L/2))

StaEVC = StaPVI + (L / 2)           (PVT=PVI+(L/2))

StaEVC = StaBVC + L                   (PVT=PVC+L)

I was looking at this again right now and I just wanted to confirm is what I have in red is what you meant (I haven't seen the notation of EC, BC before so that is why I am just confirming). 

Also, if given a horizontal curve, with the length of curve and the PI Station, can you take the PI station and subtract (L/2) to get the PC? similar for the PT but just adding it?

I know this is last minute but just want to confirm. Had a hard week at work this week and wasn't able to revise as i wanted.

Appreciate your help

 

[ptatohed]

Just to confirm,

StaBC = StaPI – T       (PC=PI-T)

StaBC = StaEC - L      (PC=PT-L)

StaEC = StaBC + L     (PT=PC+L)

Vertical Curves:

StaBVC = StaPVI – (L / 2)           (PVC=PVI-(L/2))

StaEVC = StaPVI + (L / 2)           (PVT=PVI+(L/2))

StaEVC = StaBVC + L                   (PVT=PVC+L)

I was looking at this again right now and I just wanted to confirm is what I have in red is what you meant (I haven't seen the notation of EC, BC before so that is why I am just confirming). 

Also, if given a horizontal curve, with the length of curve and the PI Station, can you take the PI station and subtract (L/2) to get the PC? similar for the PT but just adding it?

I know this is last minute but just want to confirm. Had a hard week at work this week and wasn't able to revise as i wanted.

Appreciate your help

Correct. 

BC (Begin Curve) = PC (Point of Curvature)

EC (End Curve) = PT (Point of Tangency)

BVC (Begin Vertical Curve) = PVC (Point of Vertical Curvature)

EVC (End Vertical Curve) = PVT (Point of Vertical Tangency)

(I have always much preferred the nomenclature BC/EC and BVC/EVC and that is how I prepare my plans and that's what I almost always see on other plans). 

"Also, if given a horizontal curve, with the length of curve and the PI Station, can you take the PI station and subtract (L/2) to get the PC? similar for the PT but just adding it?"

No.  You can't do this.  If you are given the PI Sta and you are looking for the BC Sta, you can only find it by subtracting the Backtangent, T, length from the PI Sta.  Your concept would only work if 2T = L, but this would never be the case, right?  Does that make sense? 

Feel free to ask any other questions. 

 

[matt267 PE]

None of that makes any sense. I hated studying transportation.

 

[ptatohed]

None of that makes any sense. I hated studying transportation.

lol!  It's the only topic I grasped well! 

 

[bulls2030]

lol!  It's the only topic I grasped well! 

i love transportation but I got a job in land development. its okay. i really loved doing transportation back in college. my senior design project was on it and its the topic i am most interested in all civil engineering topics. 

 

[bulls2030]

Correct. 

BC (Begin Curve) = PC (Point of Curvature)

EC (End Curve) = PT (Point of Tangency)

BVC (Begin Vertical Curve) = PVC (Point of Vertical Curvature)

EVC (End Vertical Curve) = PVT (Point of Vertical Tangency)

(I have always much preferred the nomenclature BC/EC and BVC/EVC and that is how I prepare my plans and that's what I almost always see on other plans). 

"Also, if given a horizontal curve, with the length of curve and the PI Station, can you take the PI station and subtract (L/2) to get the PC? similar for the PT but just adding it?"

No.  You can't do this.  If you are given the PI Sta and you are looking for the BC Sta, you can only find it by subtracting the Backtangent, T, length from the PI Sta.  Your concept would only work if 2T = L, but this would never be the case, right?  Does that make sense? 

Feel free to ask any other questions. 

I guess it does, so if i have to find the PT station and i am given the PI station and the length of the curve, i would first have to find the PC station by subtracting the tangent and then add the curve length to the PC to obtain the PT station, correct?

 

[ptatohed]

I guess it does, so if i have to find the PT station and i am given the PI station and the length of the curve, i would first have to find the PC station by subtracting the tangent and then add the curve length to the PC to obtain the PT station, correct?

Yup.  PI - T + L = EC.    If they give you the PI Sta but not T and ask for the EC Sta then they'll have to give you at least two pieces of info.  That's all you need.  Any two pieces of info can help you solve for any other curve measurements.