Horizontal curves - geometric design of roads, Civil Engineering

Horizontal Curves:

When a vehicle of mass m moves on a curve of radius R with a speed of v (m/sec) (as shown in Figure 1) it is subjected to a centrifugal force equal to:

mv2/   R

1809_Horizontal Curves - geometric design of roads.png

Figure: Forces Acting on a Vehicle on a Curve

where  m = Mass of the vehicle,

v = Speed of the vehicle in metres/sec,

R = Radius of the curve in metres,

g = Acceleration due to gravity (9.81m/sec2),

P = Side friction force resisting the centrifugal force = N µ,

N = Normal force,

µ = Coefficient of lateral friction,

α = Angle of super-elevation, and

e = Rate of superelevation, tan α.

This is counteracted by the coefficient of lateral friction (μ) and the amount by which the road is raised (super-elevation, e). It can be shown that

v2/ gR = e + μ

Expressing v as V in Km/hr,

V2/127 R= e + μ

or        R = V2/127 (e + μ)

The maximum comfortable value of e is 7 per cent (e = 0.07), and μ = 0.15.

Thus,  R =      V2/127 (0.07 + 0.15) = 0.0357 V2

For example, if a vehicle negotiates a National Highway (designed for V = 100 km/hr),

R = 0.0357 × 1002 = 357 or say 360 m.

In India, the actual value of the super-elevation to be provided on a curve is calculated on the assumption that it should counteract the centrifugal force developed at three-fourths the design speed. Thus,

V 2/127 R = e + μ

Putting μ = 0

V2/127 R= e

∴          e = (0.75 V) 2/127 R = V2/225 R

Thus,  R =V2/225 e

The road has a normal camber (1.5 to 2.5 per cent depending upon the type of surface). If this value is substituted in the above equation, the value of the radius beyond which no superelevation is required is obtained. Thus, on a black-topped road with a camber of 2.5%, and a design speed of 100 Km/hr, the minimum radius beyond which no super- elevation is required is:

 R =   100 × 100/225 × 0.025 = 1777 m, or say 1800 m

Posted Date: 1/22/2013 2:31:48 AM | Location : United States







Related Discussions:- Horizontal curves - geometric design of roads, Assignment Help, Ask Question on Horizontal curves - geometric design of roads, Get Answer, Expert's Help, Horizontal curves - geometric design of roads Discussions

Write discussion on Horizontal curves - geometric design of roads
Your posts are moderated
Related Questions

a clear illustration about working to part principle and some examples

Q. What do you mean by Stock Verification Sheets? The proper custody and accountal of stores is the prime duty and function of an executive or the stockholder. To ensure this v

What are the long spam bridge girders The pre-tensioned construction finds more use and application in the construction of those structural concrete members which are of small

Define the pre-tensioned concrete construction We understand that in the pre-tensioned concrete construction, stretched tendons are provided in the concrete moulds at the time

Can I get an online project to work on in civil engineering??

A clay layer 24 metres thick has a saturated unit weight of 18 kN/m 3 . Ground water level occurs at a depth of 4 metres. It is proposed to construct a reinforced concrete foundati

Question What is main difference in application of surface-protecting fenders and energy-absorbing fenders ? Answer Surface-protecting fenders are fenders that make

Determine about the Prestressed concrete Prestressed concrete is a special type of concrete in which internal stresses of a suitable nature, magnitude and distribution are int

Define Recommendations for confined elastomeric pad?  (a) Permissible limits for confined pressure on elastomer pad depends upon effectiveness of internal seal preventing it fr