Showing posts with label Highway. Show all posts
Showing posts with label Highway. Show all posts
EXTRA WIDENING IN HIGHWAY | TYPES |USES
Width of pavement on curved road shall will be more than width of pavement on straight road to full fill following objective:
1> To take care of off tracking due to rigidity of wheel base .
Note : Deviation of path traverse by fornt and rare axal of any vehicle on curved road is known as off tracking .
2> To counter act transverse skiding of vehicle .
3> To increase the visibility of curve .
4>To encounter psychological tendency of the driver to maintain more side gap while over taking
Extra Widening (We)= Wmech+Wphy
=nl^2/2R +V(kmph)/9.5R^.5
n -number of lane
l -length of wheel base
R- radius of circular curve
V -design speed of road
it is to be noted here that l^2/2R is off tracking where as
nl^2/2R is mechanical widening
NOTE :
1> if R > 300m then generally there is no need to provide extra widening
2> if 50< R< 300 m provide on both side of the curve .
1> To take care of off tracking due to rigidity of wheel base .
Note : Deviation of path traverse by fornt and rare axal of any vehicle on curved road is known as off tracking .
2> To counter act transverse skiding of vehicle .
3> To increase the visibility of curve .
4>To encounter psychological tendency of the driver to maintain more side gap while over taking
Extra Widening (We)= Wmech+Wphy
=nl^2/2R +V(kmph)/9.5R^.5
n -number of lane
l -length of wheel base
R- radius of circular curve
V -design speed of road
it is to be noted here that l^2/2R is off tracking where as
nl^2/2R is mechanical widening
NOTE :
1> if R > 300m then generally there is no need to provide extra widening
2> if 50< R< 300 m provide on both side of the curve .
TRANSITION CURVE IN HIGHWAY | OBJECTIVE | TYPE| CALCULATION
TRANSITION CURVE
It is provide in between straight and circular so that radius is gradually from infinite to R.
Objective of transition curve
1> To gradually introduce the centrifugal force in between straight and circular .
2> To gradually introduce super elevation and extra widening .
3> To avoid sudden jerk .
4> To enable the driven to turn the steering of vehicle gradually for comfort and security .
5> Aesthetic purpose
Types of transition curve
 |
| credit : Civil Ganeshwar |
1> Spiral or clothoid (highway)
2> Bernoulis lemniscate
3> Cubic parabola ( railway )
Ideal shape of for transition spiral clothiod because rate of change of centrifugal acceleration is constant throughout.
note : For small deviation angle behaviour of all the three types of transition curve are same .
LENGTH OF TRANSITION CURVE
1> Based on rate of change of centrifugal acceleration
LS =( V^3)/CR where V is in Kmph
where c = 80/(75+ V ) .5⥶ c ⥶ .8 where c is in m/s^3
2> Based on rate introduction of super elevation and extra widening
case A> Pavement is rotate about centre
1/N =Rate of change of superelevation
case B> when pavement is rotate about inner edge
Ls = eN(w+we)
3> Empirical formula
Ls = 2.7V^2/R ( plain and rolling area )
= V^2/R (hilly area )
As per IRC :
1> N= 150 for plain and rolling terrain
2> N= 100 for built up area
3> N = 60 for hilly area
Length of transition curve taken minimum value from case 1,case 2 and case 3 .
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