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Introduction to Transportation Engineering Instructor Dr. Norman Garrick Hamed Ahangari 17th April 2014 1 Horizontal Curve 2 Elements Δ– Intersection angle R - Radius Δ R Δ 3 Δ = Deflection Angle PI Δ R = Radius of Circular Curve L T L = Length of Curvature (L = EC – BC) BC = Beginning of Curve (PC) EC = End of Curve (PT) BC (PC) PI = Point of Intersection E T EC (PT) M C R R T = Tangent Length (T = PI – BC = EC - PI) C = Chord Length M = Middle Ordinate E = External Distance 4 Basic Definitions • BC/PC: Point of Curvature • BC = PI – T Δ – PI = Point of Intersection – T = Tangent BC (PC) Δ • EC/PT: Point of Tangency • EC = BC + L EC – L = Length 5 Degree of Curvature • D used to describe curves • D defines Radius • Arc Method: – D/ Δ = 100/L (1) (360/D)=100/(2R) R = 5730/D (2) 6 Curve Calculations Length L = 100.Δ/D (3) Tangent T = R.tan(Δ /2) Chord C = 2R.sin(Δ /2) (5) External Distance E = = R sec(Δ/2) – R (6) Mid Ordinate M = R-R.cos(Δ /2)) (7) (4) 7 Example 1 • A horizontal curve is designed with a 2000 ft. radius. The tangent length is 500 ft. and the EC station is 30+00. What are the BC and PI stations? 8 Solution • Since we know R and T we can use T = R.tan(Δ /2) so Δ = 28.07 degrees • D = 5730/R. Therefore D = 2.86 • L = 100(Δ)/D = 100(28.07)/2.86 = 980 ft. • BC = EC – L = 3000 – 980 =2020~20+20 • PI = BC +T = 2020 + 500 = 2520~25+20 9 Example 2 A curve has external angle of 20.30’ degrees, a degree of curvature is 2°30’ and the PI is at 175+00. Calculate: Radius Length of Curve BC and EC Chord External Distance Mid Ordinate 10 Solution • Given: D = 2°30’, Δ=22.30’ • Part i) Radius: 5730 R 2291 .83 2.5 • Part ii ) Length of Curve L 100 22.5 900 .00 2.5 • Part iii ) BC and EC 22.5 T 2291.38 tan 455.87' 2 BC (175 00) (4 55.87) 171 44.13 EC (171 44.13) (9 00) 180 44.13 11 • Part iv ) Chord 22.5 C 2(2291.83) sin 894.23' 2 • Part v ) External Distance 22.5 E 2291.83sec( 1 44.90' 2 • Part vi ) Mid Ordinate 22.5 M 2291.831 cos 44.04' 2 12 Example 3 The central angle for a curve is 30 degrees - the radius of the circular curve selected for the location is 2000 ft. If a spiral with k=3 degrees is selected for use, determine the i) length of each spiral leg, ii) total length of curve iii) Spiral Central Angle 13 Spiral Curves k = 100 D/ Ls Δ = Δc + 2 Δs Δs = Ls D / 200 http://www.nh.gov/dot/cadd/msv8/spiral.htm 14 Solution Given: R=2000 , Δ=30, k=3 • D = 5730/2000. Therefore D = 2.86 • L = 100(Δ)/D = 100(30)/2.86 = 1047 ft. Part i) Ls k = 100 D/ Ls, 3=100*2.86/Ls Ls= 95 ft 15 • Part ii) Total Length Total Length of curve = length with no spiral + Ls Total Length= 1047+95=1142 ft Part iii) Spiral Central Angle Δs = Ls D / 200 Δs = 95*2.86/200= 1.35 Δs =1.35 Δc= Δ- 2*Δs=30-2*1.35 Δc = 27.30 degree 16 Vertical Curve 17 Horizontal Alignment Vertical Alignment Crest Curve G1 G2 G3 Sag Curve 18 Design of Vertical Curves G1 BVC Parabolic Curve EVC G2 PI L/2 L/2 L Change in grade: A = G2 - G1 G is expressed as % Rate of change of curvature: K = L / |A| Rate of change of grade: r = (g2 - g1) / L Equation for determining the elevation at any point on the curve y = y0 + g1x + 1/2 rx2 where, y0 = elevation at the BVC x = horizontal distance from BVC g = grade expressed as a ratio r = rate of change of grade (ratio) 20 Example 1 • The length of a tangent vertical curve equal to 500 m. The initial and final grades are 2.5% and -1.5% respectively. The grades intersect at the station 10+400 and at an elevation of 210.00 m • Determine: a)the station and the elevation of the BVC and EVC points b) the elevation of the point on the curve 100 and 300 meters from the BVC point c) the station and the elevation of the highest point on the curve 21 PI BVC 2.5% EVC -1.5% 22 Solution • Part a) the station and the elevation of the BVC and EVC points – Station-BVC= 10400-250=10150~10+150 – Station-EVC=10400+250=10650~10+650 – Elevation-BVC= 210-0.025*250= 203.75 m – Elevation-EVC= 210-0.015*250= 206.25 m 23 • Part b) the elevation of the point on the curve 100 and 300 meters from the BVC point. y = y0 + g1.x + 1/2 .r.x^2, y0= 203.75, g1= 0.025 – r=(g2-g1)/L – r=(-0.015-(0.025))/500=-0.04/500 r=-0.00008 y = 203.75 + 0.025.x - 0.00004.x^2, y(100)=203.75+0.025*100-0.00004*100^2 y(100) = 205.85 y(300)= 207.65 24 • Part c) the station and the elevation of the highest point on the curve – The highest point can be estimated by setting the first derivative of the parabola as zero. • Set dy/dx=0, dy/dx= 0.025-0.0008*x=0 X=0.025/0.00008= 312.5 y(312.5) = 203.75+0.025*31.25-0.00004*(31.25)^2 y(312.5)= 207.65 25 Example 2 • For a vertical curve we know that G1=-4%, G2=-1%, PI: Station 20+00, Elevation: 200’, L=300’ • Determine: i)K and r ii) station of BVC and EVC iii) elevation of point at a distance, L/4, from BVC iv) station of turning point v) elevation of turning point vi) elevation of mid-point of each curve vii) grade at the mid-point of each curve 26 Solution -4% • i) K and r -1% – K = L / |A| – A=G2-G1, A=-4-(-1)=-3 K=300/3=100 – r=(g2-g1)/L – r=(-0.01-(-0.04))/300=0.03/300 r=0.0001 27 • ii) station of BVC and EVC – L=300’, L/2=150’ – BVC= 2000-150=1850’, ~ 18+50 – EVC= 2000+150=2150’, ~ 21+50 • iii) elevation of point at a distance, L/4, from BVC – y = y0 + g1.x + 1/2 r.x^2, – r= -0.0001, g1=0.04 – y0=200+150*0.04=206 y=206-0.04x+0.00005.x^2 L/4~ x=75 Y(75)=203.28’ 28 • iv) station of turning point – at turning point: dy/dx=0 – dy=dx=- 0.04+0.0001x=0 x(turn)=400’ • v) elevation of turning point – x=400’ – Y (400) = 206-0.04*(150)+0.00005.(150)^2 Y(400)=198’ This point is after vertical curve (Turning point is not in the curve) 29 • vi) elevation of mid-point – x=150’ – Y(150)= 206-0.04*(150)+0.00005.(150)^2 y (150)=201.12’ • vii) grade at the mid-point of each curve – Grade at every points: dy/dx= =- 0.04+0.0001x – if x= 150 Grade (150)=-0.04+0.0001*150 grade(150)= -0.025 30