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In which is the method used for a curve in India.
By radius
By arc
By chord
All of the above
By arc
In Indian surveying practice, simple circular curves are designated and defined by the Arc Definition (also known as the Arc System). Under the arc definition, the degree of a curve (D) is defined as the angle subtended at the center of the curve by an arc of a standard length, which is typically 20 meters or 30 meters.
In Indian surveying practice, simple circular curves are designated and defined by the Arc Definition (also known as the Arc System). Under the arc definition, the degree of a curve (D) is defined as the angle subtended at the center of the curve by an arc of a standard length, which is typically 20 meters or 30 meters.
R=D1718.87тАЛтЙИD1719тАЛ тАФ Radius of curve for a 30 m standard arc
R=D1145.92тАЛтЙИD1146тАЛ тАФ Radius of curve for a 20 m standard arc
D=2╧АR360┬░├ЧSтАЛ тАФ Relation between degree of curve (D) and radius (R) for arc length S
The designation of a curve establishes a direct mathematical relationship between the radius (R) and the degree of curve (D). By fixing the standard arc length (e.g., 20 m or 30 m), the degree of curve uniquely determines the radius required for field setting and layout using chain or tape measurements along the curve path.
In India, Indian Railways and Road Authorities adopt the Arc Definition for curves.
American practice predominantly uses the Chord Definition (angle subtended by a 100 ft or 20 m chord).
For flat curves (small D), the length of the chord and the length of the corresponding arc are nearly identical.
Allows easier setting out of curves along the actual curved path (alignment).
Provides uniform arc distance intervals along railways and highways.
Requires chaining directly along the arc, which can be slightly more tedious than straight chord measurements without proper offset methods.
Layout and designation of railway tracks by Indian Railways.
Highway horizontal curve design as per Indian Roads Congress (IRC) standards.
| Feature | Arc Definition (India) | Chord Definition (USA/Global) |
|---|---|---|
Definition Standard | Angle subtended by a standard arc length (20m or 30m) | Angle subtended by a standard chord length (20m or 30m) |
Formula for 30m length | R=D1718.87тАЛ | R=sin(D/2)15тАЛ |
Option A (By radius) is used in flat drafting or general specification, but for surveying field designation and curve setting in India, the degree is defined by the arc definition.
Option C (By chord) is the standard chord definition mostly followed in American practice.
Option D is incorrect as the standard official designation in Indian engineering practice specifically uses the arc method.
B is correct тАФ In India, curves are standardly designated and measured using the arc definition method based on a 20 m or 30 m arc length.
For Indian competitive exams like SSC JE and GATE, remember RтЙИ1720/D for 30m chain and RтЙИ1150/D for 20m chain to solve numericals quickly without a calculator.