infrastructure - i horizontal curves.pptx

7/27/2019 INFRASTRUCTURE - I HORIZONTAL CURVES.pptx

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INFRASTRUCTURE - I

MODULE 3: HIGHWAY GEOMETRICS


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TERMS

1. RIGHT OF WAY

2. FORMATION WIDTH

3. ROAD MARGIN

4. ROAD SHOULDER

5. CARRIAGE WAY

6. SIDE SLOPES

7. KERBS

8. FORMATION LEVELS9. CAMBER

10. GRADIENT


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TERMS

1. DESIGN RUNNING SPEED

2. AVERAGE RUNNING SPEED

3. STOPPING SIGHT DISTANCE4. PASSING SIGHT DISTANCE


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NECCESSITY OF CURVES

WHY HORIZONTAL CURVES?

SMOOTH AND SAFE DRIVING ESPECIALLY

FOR HIGH SPEED TRAFFIC

WHY VERTICAL CURVES?

SAFETY AND COMFORT OF TRAVELLINGOVER VERTICAL GRADIENTS


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DESIGN OF HORIZONTAL CURVES


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GENERAL GUIDELINES


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GENERAL GUIDELINES


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GENERAL GUIDELINES


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GENERAL GUIDELINES:

GOOD AND BAD ALIGNMENT


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DEFINATIONS AND NOTATIONS

APEX OF A CURVE(VERTEX) P.I.

APEX DISTANCE (Es)

CURVE RADIUS (R)

INTERSECTION ANGLE(180- )

LONG CHORD (L.C.)

LONG TANGENT (L.T.) SHIFT (S)

SHORT TANGENT (S.T)

TANGENT DISTANCE (T)

TANGENT POINT (T.P)

TOTAL DEVIATION ANGLE()

TRANSITION LENGTH (Ls)

C.C.T. Point

C.T. & T.C. Points


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DEFINATIONS AND NOTATIONS


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OVERVIEW OF GEOMETRIC DESIGN

CONSIDERATIONS

STEP 1:

DECIDING DESIGN SPEED

BASED ON ROAD CLASSIFICATION


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CONSIDERATIONS

STEP 2: DESIGNING CIRCULAR CURVE RADIUS

FORCES ON THE VEHICLECENTRIFUGAL FORCE

DUE TO MOTION, WEIGHT, REACTION OF THE

ROAD

INWARD TILT OF THE ROADSUPERELEVATION

FRICTION BETWEEN TYRE AND ROAD

MINIMUM CURVE RADIUSMIN TURNING

RADIUS OF VEHICLE, SPEED, FRICTION &

SUPERELEVATION


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CONSIDERATIONS

STEP 3: SUPERELEVATION

WHY?

HOW MUCH? Max= 0.07 to 0.1 Superelevation charts for various design speeds

and curve radius

How to build superelevation?


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CONSIDERATIONS

STEP 4: WIDENING PAVEMENTS ON CURVES

VEHICLE requirements

Pscychological requirements How to widen?


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GEOMETRIC DESIGN HORIZ CURVE

STEP 1:DECIDING DESIGN SPEED

HIGHER TRAFFIC VOLUMEMORE DESIGN SPEED

TOO LOW OVERALL SPEEDUNECONOMIC POTENTIAL SPEED OF VEHICLETOO COSTLY TO

DESIGN

So what to adopt?

Max approx uniform speed that will probably be

adopted by faster group of drivers

for the given classification of the road


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STEP 1:DECIDING DESIGN SPEED contd

FUNCTION OF THE ROAD

TERRAIN ** major factor for G.D.

Minor stretches to be ignored

Ruling speed is mentioned

Minimum speed specified where poor site

conditions


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FORCES ON THE VEHICLE

CENTRIFUGAL FORCE DUE TO MOTIONVehicle travels a constant radius at constant speed

Radial outward force

P= W v2/ g R Take g = 127 to match units

WEIGHT OF VEHICLE W

REACTION OF THE ROAD R


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P P

W R W R


INWARD TILT OF THE ROADSUPERELEVATION

Thus,Super-

elevation

balances

centrifugalforce.


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How much super elevation to provide?

Centrifugal ratio = B = P/W = V2/127 R

is angle of friction between tyre and road

Tan A = P/W B= V2/127 R = tan (A+ )

= tan A + tan

= e+f(super elevation + friction)


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How much super elevation to provide?

For heavy vehicles (bullock cart) with high cg,

more than 70% transverse slope inconvenient.

Maximum allowable superelevation = 7%

In hilly areas, such carts are not permitted, so

high superelevation upto 10% is permitted (if

no snow)

On hills with snow, max e = 7 %


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How much friction? B= V2/127 R = e+f

fdepends on?

Vehicle speed

Type and condition of road

Condition of tyre

Weather and temperature of road

What is the value off?

When muddy, f can be as low as 0.2 Assuming FOS = 1.5, take f = 0.15

Can we controlf?


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Design speed

Allowable superelevation and friction

Minimum turning radii of vehicle

B= V2/127 R = e+f

Max B = 0.07 + 0.15 = 0.22 or 0.25Thus sharpest curvature

R = 0.0358 V20.0315 V2

GEOMETRIC DESIGN HORIZ CURVESTEP 2: DESIGNING CIRCULAR CURVE RADIUS

MINIMUM CURVE RADIUS


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Q. If design speed = 40 kmph and plain terrain whatis the min curve radius we should provide? 60 m

So should we provide 60 m?

Designer to provide max possible. Minimum turning radius of vehicle Public service vehicle:

Veh length Turning dia

< 8.23 m 19.812 m

8.2310.973 m 21.641 m> 10.973 23.774 m

Commercial vehicle: Generally 1221 m dia

Car : 7.613.7 m dia

PROVIDE MIN 26 m TURNING RADIUS

GEOMETRIC DESIGN HORIZ CURVESTEP 2: DESIGNING CIRCULAR CURVE RADIUS


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CENTRIFUGAL FORCE e and/or f

Iffnot sufficient, vehicle may skid. Tyre damage

Accident

Pavement damage Superelevation gives maintenance economy.

How?


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STEP 3: SUPERELEVATION Two design approaches:

1. e to counteract full centrifugal force

2. e to counteract a part of centrifugal force

Which is more desirable and why?

What is the percentage centrifugal ratio

counteracted by e on plain terrain?

0.07 /(0.07+0.15) x 100 = 32 %


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Provide e to counteract centrifugal

force due to of design speed.

Design e = (0.75 V)2/ 127 R

= (V)2/ 225 R


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CAMBER & SUPERELEVATION

Specified FOR DRAINAGE

If e required is less than camber required,

there may be no superelevation

What happens when you have normal

camber on the curve?

Outer side of curve has negativesuperelevation

The max negative superelevation allowed is

0.03.


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How to provide super elevation?


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Where is max superelevation ?

If e = V2/225 R

Max permissible e = 0.07

R = 0.06349 V

2

Min permissible radius = 0.0358 V2

Thus max e will occur on transition curve, we

have to mark this point while laying the curve. Alternatively superelevation may be designed

to be max at end of transition curve.


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STEP 4: WIDENING PAVEMENTS ON

CURVES

1. VEHICLE requirements

Mechanical widening = l2/2R

l is the wheel base

R is the radius of the curve

1. Psychological widening = V / 9.5 R


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Mechanical widening

infrastructure - i horizontal curves.pptx

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