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
• The previous load analysis represents a first and necessary step in the analysis of the given structure but it does not tell us whether the given load can be safely supported (i.

Example for Productivity Analysis and Improvement An excavator with a bucket capacity of 3-yd 3 has a standard production rate of 2,160-yd 3 for an 8-hour day.  The job site

Question What is the sucker deck principle for changeable depth bridge decks ? Answer For a variable depth bridge deck, depth of continuous multi-span bridge deck is greate

Joints in box culverts and channels - necessity of water tightness The joints for box culverts and channels must be capable of accommodating movements arising from moisture an

Use of Admixtures in Concrete The use of chemical admixtures may be made in prestressed concrete construction. But the admixture should not contain chlorides in any form. This

Define Permissible Bearing Pressure on poly tetra fluoro ethylene? For the purpose of design, it is important to lay down permissible bearing pressure on PTFE sliding surfaces.

Using an optical square how would you perform a rectangular tie?

Define Hardness - Chemical Characteristics of Water Caused by any polyvalent cations (mainly Calcium and Magnesium). Expressed as mg/l as CaCO 3 . Causes precipitates with soap