Skip to main content

Rankine's method table, 150° intersection, 3°

Short answer

Deflection angle Δ = 30°, degree of curve 3° for 20 m chord gives radius R = 180×20/(π×3) = 381.97 m. Tangent T = 102.35 m, curve length L = 200.00 m. T₁ chainage 1482.65 m, T₂ 1682.65 m. Deflection angles are computed per chord using δ = 1718.87c/R minutes, with final cumulative angle 15°00′00″.

Compute and tabulate the data required for setting out a simple circular curve by Rankine's Method from the following information: Angle of intersection = 150°00' Chainage of point of intersection = 1585.00 m Degree of curve = 3° Peg interval = 20 m, Normal chord = 20 m

Angle of intersection (interior) = 150°, so deflection angle Δ=180∘−150∘=30∘\Delta = 180^\circ - 150^\circ = 30^\circ. The degree of curve is taken for the normal chord (arc) of 20 m.

Elements

R=180 CπD=180×20π×3=381.97 mT=Rtan⁡Δ2=381.97tan⁡15∘=102.35 mL=πRΔ180=200.00 m\begin{aligned} R &= \frac{180\,C}{\pi D} = \frac{180\times 20}{\pi\times 3} = 381.97\ \text{m}\\ T &= R\tan\frac{\Delta}{2} = 381.97\tan 15^\circ = 102.35\ \text{m}\\ L &= \frac{\pi R\Delta}{180} = 200.00\ \text{m} \end{aligned} Chainage of T1=1585.00−102.35=1482.65 mChainage of T2=1482.65+200.00=1682.65 m\begin{aligned} \text{Chainage of T}_1 &= 1585.00 - 102.35 = 1482.65\ \text{m}\\ \text{Chainage of T}_2 &= 1482.65 + 200.00 = 1682.65\ \text{m} \end{aligned}

Rankine's deflection angles

δ=1718.87 c/R\delta = 1718.87\,c/R minutes for a chord cc. First sub-chord c1=17.35c_1 = 17.35 m (to the next 20 m peg), last sub-chord cn=2.65c_n = 2.65 m.

Point (chainage, m)Chord c (m)δ = 1718.87c/RCumulative deflection
1482.65--0°00′00″
1500.0017.351°18′04″1°18′04″
1520.0020.001°30′00″2°48′04″
1540.0020.001°30′00″4°18′04″
1560.0020.001°30′00″5°48′04″
1580.0020.001°30′00″7°18′04″
1600.0020.001°30′00″8°48′04″
1620.0020.001°30′00″10°18′04″
1640.0020.001°30′00″11°48′04″
1660.0020.001°30′00″13°18′04″
1680.0020.001°30′00″14°48′04″
1682.652.650°11′56″15°00′00″

Check: final deflection =Δ/2=15∘00′00′′= \Delta/2 = 15^\circ00'00'' (computed 15°00′00″).

Answer: R=381.97R = 381.97 m, T=102.35T = 102.35 m, L=200.00L = 200.00 m, T₁ at 1482.65 m, T₂ at 1682.65 m; deflection angles as tabulated.

✓ Answer checked by Claude Opus 5.5 (high effort)

All Surveying II chapter 6 questions →