Horizontal curves - geometric design of roads, Civil Engineering

Assignment Help:

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


Related Discussions:- Horizontal curves - geometric design of roads

One layered spatial structures, Classification of the damage according to t...

Classification of the damage according to the type of structures The level of damage in spatial trusses has also been classified into three different levels based on th

Explain what is stationing - transportation, Explain what is Stationing - T...

Explain what is Stationing - Transportation 1) Stationing concept is used along horizontal alignments for referencing purpose 2) 1 station = 100 feet 3) How do you repres

Determine the normal and shear stress elements, Determine the normal and sh...

Determine the normal and shear stress elements: The state of stress at a point is given through the stress components σ x = 70 MPa, σ y = 10 MPa, and τ xy = - 40 MPa. Using

What do you mean by ozone test, Q. What do you mean by Ozone Test? Some...

Q. What do you mean by Ozone Test? Some research and studies determined that the ozone test was unnecessary as this affects only the surface layer.  In un-stretched rubber, ozo

Building classification, Why I is the missing after h and J is written in t...

Why I is the missing after h and J is written in the classification of building

Explain pressure balance method and compressed air method, Pressure balance...

Pressure balance method vs. compressed air method in pipe jacking Pressure balance method generally requires the use of mechanically operated tunnel-boring machine at its cutti

Explain the angle of wall friction, A retaining wall 4.5 m high with vertic...

A retaining wall 4.5 m high with vertical back supports a backfill with horizontal surface. The unit weight of the fill is 18 kN/m 3 and the angle of internal friction is 36°. The

Calculate the total duration for the four activity project, Calculate the T...

Calculate the Total Duration for the Four Activity Project Solution:      Scheduling work activity has associated time duration. The durations shown in the Table were e

Explain census of traffic at level crossings, Q. Explain Census of Traffic ...

Q. Explain Census of Traffic at Level Crossings? Periodical census of traffic at all level crossings, unmanned/manned should be taken at least once in five years to review the

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd