120 Solved Surveying Problems, Problem #48.

[palvarez83]

Hey guys and gals I'm having trouble distinguishing what a deflection angel is. My understanding is that the deflection angle is supposed to be half the intersection angel: α =I/2. However, in the example below what they are referring to as the deflection angel appears to be I. Why is that? What am I missing in my understanding? Is it different if the "deflection angel" is given at PI instead?

Here is the wording:

A horizontal curve has a degree of curvature of 2°30'00". The stationing at the point of intersection is sta 23+44.78. The deflection angle of the curve at PI is 12°00'00". The stationing at the beginning of the curve (BC) is...

The solution involves first finding the curve radius from the degree of curvature... R =2,291.83. Then the tangent distance is found using T = R tan(I/2). The tangent distance is then subtracted from the stationing at PI. In the solution they evaluate T = 2291.83 Tan(12°/2). This is where I am mistaken with the wording. Why isn't it T = 2291.83 Tan(6°/2) considering they gave us a deflection angle not an intersection angle?

Thanks in advance,

P.A.

 

[palvarez83]

It is interesting to note that the next problem # 49 is referring the the same horizontal curve. However, on that one they word it slightly differently (more clearly) as follows:

The deflection angle of the curve at the point of intersection, I, is 12°00'00".

From there one could understand it is I that is given rather than α =I/2.

 

[civilized_naah]

See this thread

http://engineerboards.com/index.php?showtopic=13716

 

[palvarez83]

Thanks. Looks like I'm not the only one then... :hang: