Month: November 2018

Stopping Or Non-Passing Or Headlight Sight Distance

Stopping or non-passing or headlight sight distance is the distance required by a driver of a vehicle travelling at a given speed to bring his vehicle to a stop after an object on the road becomes visible. It is made of two components:

i) The distance travelled during the total reaction time i.e. the lag distance.
ii) Breaking distance

Therefore ,Stopping sight distance(Non Passing Or Headlight Sight Distance) = Lag distance + Breaking distance(in m)
= 0.278 Vt + V²/254f .

When there is an ascending gradient (+ n %) or descending gradient (- n %),the above equation becomes:

Stopping Sight Distance(Non Passing Or Head Light Sight Distance) = 0.278 Vt + V²/254(f ± 0.01n).

On roads with restricted width or on single-lane roads when two-way traffic movement is permitted then the minimum stopping sight distance should be equal to twice the stopping sight distance calculated above.

Read more:

Overtaking Zone

Braking Distance (How To Calculate Braking Distance)

Braking Distance

It is the distance traversed by a vehicle between the points, at which brakes are applied and the point at which the vehicle comes to stop.

How To Calculate Braking Distance

Braking distance may be obtained by equating the work done in stopping the vehicle and the kinetic energy. If v is the design speed of the vehicle in m/sec, f is the coefficient of friction, W is the total weight of the vehicle and g is the acceleration due to gravity = 9.81 meter per second square, I is the braking distance then:

kinetic energy at design speed = [latex] \frac{mv^{2}}{2} = \frac{Wv^{2}}{2g} [/latex]

Work done against friction force in stopping the vehicle = f.W. I

Hence, f.W.I = [latex] \frac{Wv^{2}}{2g} [/latex]

or, I = [latex] \frac{v^{2}}{2gf} [/latex]

If V is the speed of the vehicle in kilometre per hour(Kmph), then

When (V) speed in Kmph then, v =0.278V

Wear of Rails And Their Classification

Wear of Rails

The reduction in cross-sectional dimensions or weight of rails in the form of flow rail material, battering at rail ends etc.is known as wear of rails.

Classification of Wear of Rails

Wear of rails can be classified in accordance with the location and position of wear

A. On the Basis of Location

The wear is prominent in the following locations:
1. On sharp curves.
2. On gradients.
3. On approaches to stations.
4. In tunnels.
5. In the coastal area.
6. On a weak foundation.

B. On the Basis of the Position of Wear

The following are the positions of wear of rails.
1. Wear on top or head of rails.
2. Wear at the ends of the rails.
3. Wear on the sides of the head.

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Methods To Reduce Wear of Rails

Creep of Rails

11 Methods to Reduce Wear of Rails

In addition to coning of wheels and providing proper superelevation curves, the following methods are employed to reduce the wear of rails:

By using the special alloy steel rails at places where wear is considerable.
By regular tightening of fish bolts and packing of ballast.
By reducing the number of joints by welding.
By welding or de-hogging battered ends of rails in time.
By regular maintenance of track with special attention to the joints.
By maintaining the correct gauge.
By using bearing plates.
By lubricating the gauge face of the outer rail on curves regularly.
By interchanging the inner and outer rails and changing faces at curves.
By providing check rails at curves.
By application of heavy mineral oil under an adverse atmosphere.

Read More:

Creep of Rails

Wear of Rails And Their Classification

Overtaking Zone || Highway Engineering

Overtaking Zone

There may be stretches of road where the safe overtaking distance can not be provided. In such cases, overtaking opportunities for vehicles moving at a design speed should be given at frequent intervals. These zones which are meant for overtaking, are called overtaking zones.

The minimum length of overtaking zone should be three times the safe overtaking distance i.e., 3(d1+d2) for one-way traffic & 3(d1+d2+d3)for two-way traffic.

[O.S.D = Overtaking Sight Distance ]

O.S.D =(d1+d2) for one way traffic=(d1+d2+d3) for two way traffic.

SP1 = Sign Post ” Overtaking zone ahead”

SP2 = Sign Post “End of Overtaking zone”

Read more:

Types of roads

Kerbs

Length of Summit Curve Design Method

Length of Summit Curve

The length of the summit curve is designed based on the two criteria:

i) Considering the stopping sight distance.
ii) Considering the safe overtaking sight distance or intermediate sight distance.

i) Considering the Stopping Sight Distance

The length of summit curve(L) according to this criteria may be determined for the two conditions:

a) When the total length of the summit curve (L) is greater than the stopping sight distance(S).

b) When the total length of the summit curve (L) is less than the stopping sight distance.

When the total length of the summit curve (L) is greater than the stopping sight distance, the value of L(length of summit curve) is calculated from the following equation:

L = NS²/(√2H + √2h)²

Where,
H = is the height of eye level of the driver above the roadway surface in m.
h = is the height of the object above the pavement surface in m and N is the deviation angle.

When the total length of the summit curve (L) is less than the stopping sight distance, the value of L(length of summit curve) is calculated from the following equation:

L = 2S – (√2H + √2h)²/N

ii) Considering the safe overtaking sight distance or intermediate sight distance

The length of summit curve(L) according to this criteria may be determined for the two conditions:

a) When the total length of the summit curve (L) is greater than the overtaking or intermediate sight distance (S).

b) When the total length of the summit curve (L) is less than the overtaking or intermediate sight distance (S).

When the total length of the summit curve (L) is greater than the overtaking or intermediate sight distance (S), the value of L is calculated from the following equation:

L = NS²/8H

When the total length of the summit curve (L) is less than the overtaking or intermediate sight distance (S), the value of L is calculated from the following equation:

L = 2S – 8H/N

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Length of Valley Curve

Length Of Transition Curve

Length of Valley Curve Design Method

Length of Valley Curve

The length of the valley curve is designed on the basis of two criteria:

i) The allowable rate of change of centrifugal acceleration of 0.06 m/sec.
ii) The headlight sight distance.

The higher of the two values is adopted.

Criteria (i)

The length of valley transition curve (Ls) according to the first criteria is given by the following equation:

Ls = [ Nv³ /C]^1/2

Where N is the deviation angle,v is speed in m/sec and C is the allowable rate of change of centrifugal acceleration. The length of the valley curve (L) is taken to 2Ls.

Criteria (ii)

The length of valley curve (L) according to the second criteria may be determined for two condition

1. When the total length of valley curve (L) is greater the stopping sight distance.

2. When the total length of valley curve (L) is less than the stopping sight distance.

When the total length of valley curve (L) is greater than the stopping sight distance, the value of L is calculated from the following equation.

L = NS² /(2h1 + 2Stanα)

Where h1 is the height of headlight, is the angle of inclination of the beam of light, S is the stopping sight distance and N is the deviation angle.

When the total length of valley curve(L) is less than the stopping sight distance, the value of L is calculated from the following equation:

L = 2S – (2h1 + 2Stanα )/N

Read more:

Length of Summit Curve

Length Of Transition Curve

10 Requirements Of An Ideal Rail Joint

Rail Joints

The meeting place of any two adjoining rails in a railway track is known as rail joint. Rail joints are necessary to hold together the adjoining ends of the rails in the correct position.

Rail joints from the weakest part of the track. It is observed that the strength of a rail joint is only 50% of the strength of a rail.

10 Requirements Of An Ideal Rail Joints

The following requirements should be met by an ideal rail joint:

1. Both the adjoining rail ends at the joint should remain true in line both laterally and vertically when the train passes over the joint.

2. The rail joint should be as strong and stiff as the rail itself.

3. It should be elastic both laterally and vertically so that vibrations and shocks can be absorbed.

4. It should provide enough space for free expansion and contraction due to temperature variation.

5. It should facilitate easy removal and replacement of rails without disturbing the whole track.

6. It should not allow the rail ends to get battered in any case.

7. It should be economical in its cost of construction as well as maintenance.

8. Joints ought to be universal type so that they can be utilized for all kinds of sleepers.

9. It ought to give protection from longitudinal forces created because of increasing speed(acceleration), and deceleration to reduce the creeping effect.

10. It should be enduring.

Read More:

Creep of Rails

Types of Rails

Hogged, Buckling and Tilting of Rails

Factors Governing the Length of Rail

The standard rail lengths prescribed on Indian railways are given below:

12.80 m (42 ft) length for Broad gauge.
11.89 m (39 ft) length for Meter Gauge.

The length of rails is governed by the following factors:

1. Cost: The length of the rails is so chosen that the manufacturing cost is most reasonable.

2. Transportation: Transportation facilities available.

3. Train Speed and Capacity: The length of the rails also depends on the speed of the trains and the expected number of train operations per day. In the case of higher-speed trains, shorter rail length is best as it can prevent excessive vibration and likely safety hazards.

4. Maintenance and inspection: Smaller rail sections make it easier to identify and fix problems such as wear, cracks or damage. Whereas long lengths of rails require frequent inspection and maintenance as they are more likely to break, wear, or damage.

5. Lifting and handling: Lenth of the rail also depends on the facilities available for lifting and handling of the rails. Hence the length of the rails should be such that they do not pose any difficulty in lifting and handling.

6. Reasonable expansion gap at rail joints.