What is super elevation?
The lateral inclination of the road is known as superelevation. Superelevation is provided to reduce the tendency of the vehicle to topple or skid, the outer edge of the road pavement is raised with respect to the inner edge, thus tilting the road surface from the outer edge tower to the inner edge. It is denoted by “e”.
If superelevation is not provided at horizontal curves, then the load on the outer wheel shall be more than the load on the inner wheel.
What are the factors on which superelevation depends?
Superelevation of the road depends upon the following factors.
- Speed of vehicle on the curves.
- Radius of the horizontal curves.
- Lateral friction resistance between vehicle tyres and road.
The centrifugal force always acts on a horizontal even vehicle running on a superelevation track. and the superelevation is expressed as the ratio of the height of the outer edge with respect to the horizontal width of the pavement.
W = width
or, sin θ = E/W
So, tanθ = E/W = “e”
or, e = E/W , [where maximum value of e = 7%]
Analysis of Super Elevation
P cos θ = wsin θ + F
or, Pcos θ = W sin θ + FA +FB [ Since FA = FA + FB = f( RA + RB )]
or, Pcos θ = W sin θ + f( RA + RB )
or, Pcos θ = W sin θ + f( W cos θ + P sin θ ) [Where, RA + RB = ( W cos θ + P sin θ ) ]
or, Pcos θ – F Pcos θ = w sin θ + Fw cos θ
Dividing both side by “w cos θ” then,
Here, consider, e = 7%=0.07 and f = 0.15 then,
(1-fe) = 1
How do you calculate super elevation?Design steps
- Considering 75% of design speed and neglecting coefficient of lateral friction (f) so,
2. If e>0.07 from step (1) then take e=0.07 & obtain f by,
3. If f> 0.15 from step (2), calculate restricted velocity Vo by taking e = 0.07 and f= 0.15
Superelevation Problems and solutions
Q) The design speed of the highway is 75 km/hr and the radius for horizontal curve is 140 m.
a) Calculate the superelevation needed to maintain that speed.
b) If the maximum superelevation is 7% then calculate allowable speed on this curve.
a) First take 75% of design speed,
Here, e > 7%
b) So, use e = 7% = 0.07
f is . 0.15 So,
Taking f = 0.15 and e = 0.07 to get restricted velocity.
For the purpose and safety, provide Vo=60 Km/hr.
I hope this article on “ How do you calculate super elevation ” remains helpful for you.
Happy Learning – Civil Concept