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Rankine's deflection angle data, 145°, 5°

Short answer

Deflection angle Δ = 35°, degree 5°/30 m arc gives R = 1718.87/5 = 343.77 m. T = 108.39 m, L = 210.00 m. T1 = 1471.61 m, T2 = 1681.61 m. Deflection angles by δ = 1718.87c/R min, rounded to 10″; final cumulative = Δ/2 = 17°30′00″.

Compute the data for setting out a simple circular curve by Rankine's deflection angle method from the following informations: Angle of intersection = 145°0' Chainage of point of intersection = 1580 m Degree of curve = 5° Least count of the theodolite = 10" Peg interval = 30 m

Angle of intersection (interior) = 145°, so deflection angle Δ=180∘−145∘=35∘\Delta = 180^\circ-145^\circ = 35^\circ. Degree of curve 5° for a 30 m arc.

Elements

R=1718.87D=1718.875=343.77 mT=Rtan⁡Δ2=343.77tan⁡17.5∘=108.39 mL=πRΔ180=210.00 mCh. of T1=1580−108.39=1471.61 mCh. of T2=1471.61+210.00=1681.61 m\begin{aligned} R &= \frac{1718.87}{D} = \frac{1718.87}{5} = 343.77\ \text{m}\\ T &= R\tan\frac{\Delta}{2} = 343.77\tan 17.5^\circ = 108.39\ \text{m}\\ L &= \frac{\pi R\Delta}{180} = 210.00\ \text{m}\\ \text{Ch. of T}_1 &= 1580 - 108.39 = 1471.61\ \text{m}\\ \text{Ch. of T}_2 &= 1471.61 + 210.00 = 1681.61\ \text{m} \end{aligned}

Deflection angles

δ=1718.87 c/R\delta = 1718.87\,c/R minutes, rounded to the least count of 10″. Peg interval 30 m: first sub-chord =28.39= 28.39 m, last sub-chord =1.61= 1.61 m.

Point (chainage, m)Chord c (m)δ = 1718.87c/RCumulative deflection
1471.61--0°00′00″
1500.0028.392°22′00″2°22′00″
1530.0030.002°30′00″4°52′00″
1560.0030.002°30′00″7°22′00″
1590.0030.002°30′00″9°52′00″
1620.0030.002°30′00″12°22′00″
1650.0030.002°30′00″14°52′00″
1680.0030.002°30′00″17°22′00″
1681.611.610°08′00″17°30′00″

Check: final deflection =Δ/2=17∘30′00′′= \Delta/2 = 17^\circ30'00''; the table gives 17°30′00″.

Answer: R=343.77R = 343.77 m, T=108.39T = 108.39 m, L=210.00L = 210.00 m; T₁ = 1471.61 m, T₂ = 1681.61 m; deflection angles as tabulated.

✓ Answer checked by Claude Opus 5.5 (high effort)

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