I represent intersection angle, central angle of curve or deflection angle between back and forward tangents...It is part of the problem in Horizontal Curves. See prob.78.1 CERM. Also page 78-2 CERM
That solution has been changes, see the errata.
In the question, the sentence 2 has changes as:
The elevation of the hydraulic grade line is 495 ft at the beginning of the pipe and 365 ft at the end of the pipe.
All the solution has been change too.
I used two references by the same author (Ruwan Rajapakse):
- Civil PE Exam Construction Module (Third Edition).
- Civil PE Exam Construction Module. Practice problems.
But take care, there are a lot of mistakes in those books.
I had the same problem, I found the solution:
The stair concentrated load is: 0.45 kips x L inc, and L inc = 20 ft / cos (angle), cos (angle) = 20 ft / 25.9278 ft = 0.7714