practice problems cerm 11th ed construction question

[gcj]

breadth problem 6 in chapter 80... can anybody explain the solution to this problem that the book gives?

i have little exp in stakeouts which is maybe the reason why i don't get why they only add the length of the tangent to the intersection of the 2 centerlines to get the station to put the stakeout. to me, if this was a different problem and the width of the minor road was a lot wider, then the station where they put the stakeout would just be some random point.

why don't they take into account the additional length added by the width of the intersecting road to place the stakeout at the station perpendicular to the beginning of the curve or place it at the station perpendicular to the end of the curve at point A? or even where the PI of the curve is?

maybe i'm reading into this more than i should? maybe the book is wrong? maybe i'm reading the problem wrong? i don't know. my brain is fried...

help!!!

 

[gripper]

I am also confused by the solution given. It seems to me that the R used in their solution should have been 48' (30' + 1/2 the width of 23rd St), which by my calculations would have resulted in a PC sta. of about 6+10. ....??

 

[gcj]

I am also confused by the solution given. It seems to me that the R used in their solution should have been 48' (30' + 1/2 the width of 23rd St), which by my calculations would have resulted in a PC sta. of about 6+10. ....??

exactly what i was thinking...thanks!

 

[JohnathanT]

exactly what i was thinking...thanks!

I thought the same thing at first, but I think the reason they use R=30' instead of 48' is b/c the question asks where the stake is to be placed to layout point A, not where the PC of the curve actually hits. I may be wrong, but I think that's the reasoning behind this problem. Anyone else agree or disagree? I'd be happy to hear other opinions.

 

[petobe]

I agree with the first 3 posts... it doesn't make sense. They are asking for the position of the PC curb return, and then for some reason add the tangent distance of the 30' curve to the PI station of th 48' curve. The PI location of the 30' radius curve does not coincide with the PI of the 48' radius curve

 

[gcj]

I thought the same thing at first, but I think the reason they use R=30' instead of 48' is b/c the question asks where the stake is to be placed to layout point A, not where the PC of the curve actually hits. I may be wrong, but I think that's the reasoning behind this problem. Anyone else agree or disagree? I'd be happy to hear other opinions.

i thought of this also, but i couldn't find the logic of placing the stakeout at this location, esp since it doesn't really coincide w/ n e valid ref points...like y can't u put it at the intersection of the baselines n call it out at that stakeout or something.

 

[maverick_tlc]

Yes, the book is WRONG. We know it. You can even draw it to scale (I did) and see the answer is roughly 6+10. I've been very UNIMPRESSED with the quality of the study materials given how much they cost. Erratta is UNACCEPTABLE in books costing this much (especially as many as the CERM has, including problems just being worked out WRONG).

It has nothing to do with the whole "curb" vs "street intersection" thing. If you draw tangents to the curb, you are still defined off of the Elm Street Stationing (and any side to side location i.e. at the curb vs at the center line is still defined as being at Station x+xx, just "off set".) I've complained to Lindburgh about the 11th edition and all the erratta already. Ya'll should too. And IF you did work this as a 30' curve problem, then the PI simply "slides" about 30 feet down Elm Street towards point A... so the 44 ft plus the 30 foot slides put you right back at 6+10-ish.

 

[crogmobulon]

Yes, the book is WRONG. We know it. You can even draw it to scale (I did) and see the answer is roughly 6+10. I've been very UNIMPRESSED with the quality of the study materials given how much they cost. Erratta is UNACCEPTABLE in books costing this much (especially as many as the CERM has, including problems just being worked out WRONG).
It has nothing to do with the whole "curb" vs "street intersection" thing. If you draw tangents to the curb, you are still defined off of the Elm Street Stationing (and any side to side location i.e. at the curb vs at the center line is still defined as being at Station x+xx, just "off set".) I've complained to Lindburgh about the 11th edition and all the erratta already. Ya'll should too. And IF you did work this as a 30' curve problem, then the PI simply "slides" about 30 feet down Elm Street towards point A... so the 44 ft plus the 30 foot slides put you right back at 6+10-ish.

I ran into the same problem. Found and printed out the errata for this edition from the publisher. They know about it, and their comment is:

"p. 80-3, first column, Solution 6: This problem will be rewritten for clarity. In the meantime, if you used geometry to calculate a PCR of 6+9.88 sta, you did well. 5/8/2009"

Still doesn't tell me how you get there, but some of the above comments are helpful.