Hi,
Super-elevation: It is the inward transverse slope provided throughout the length of the horizontal curves to counteract the centrifugal force and therefore to check the tendency of the vehicle to overturn or skid.
The outer edge of the pavement is raised with respect to the inner edge of the pavement, the ratio of the height raised to the width of the pavement is called super-elevation.
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| Superelevation on the horizontal curves |
e = E/B = tan(angle w.r.t. horizontal)
Or E = e.B
e+f = v^2/ g.R
Here, e = rate of super-elevation
f= design value of the lateral friction co-efficient = 0.15
v = speed of vehicle in m/sec.
R= Radius of the horizontal curve, m
If velocity is in Kmph, then
e+f = V^2/(127.R)
Also Read: Highway Geometrics- Camber, Land Width, Carriage way, Sight Distance, Super Elevation, Gradient
Methods of Providing Super-elevation
Superelevation is provided at a gradual rate along the length of the transition curve. It is done by changing crowned camber a single cross slope before the start of the circular curve. Full superelevation is attained at the end of the transition curve or at the start of the circular curve.
Attainment of the Superelevation may be completed in the following steps.
(i) Elimination of the crown of the cambered section.
(ii) Rotation of the pavement to attain a full super-elevation.
The second step can be completed in three ways,
(a) by rotating the pavement with respect to the inner edge,
(b) by rotating the pavement with respect to the centre of the pavement or
(c) by rotating the pavement with respect to the outer edge of the pavement.
Superelevation is introduced by rising in the outer edge of the pavement at a rate not exceeding 1 in 150 in plain and rolling terrain and 1 in 60 on mountainous and steep terrain as per the recommendations of the IRC(Indian Roads Congress).
Also Read: Highway Geometrics- Camber, Land Width, Carriage way, Sight Distance, Super Elevation, Gradient
Designing Superelevation
The design procedure for providing the superelevation follows the following Four steps:
(1) Friction is neglected and super-elevation is designed for 75% of the design speed value,
e = (0.75. v)^2/ (gR) where v is in m/sec
or e = (0.75. V)^2/ (127R) where v is in Kmph/sec
(2) If e < 0.07 then value so obtained is provided
If e>0.07, then provide the maximum super-elevation equal to 0.07 and proceed with steps 3 and 4.
(3) Check the co-efficient of friction developed for the maximum value of e equal to 0.07 for the full design speed v.
f= v^2/(g.R) – 0.07
if f< 0.15, then e = 0.07 is safe for the design speed. If not, calculate the restricted speed as follows
(4) 0.07 + 0.15 = Va^2/ (g.R)
Where, Va = allowable safe speed.
Also Read: Highway Geometrics- Camber, Land Width, Carriage way, Sight Distance, Super Elevation, Gradient
Thanks for your visit!
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