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The length of normal chord is___
10 m
15 m
20 m
25 m
20 m
In route surveying, a normal chord (also known as a full chord) is defined as the standard full chain length chord between two consecutive main stations along a circular curve ┬╖ In standard Indian surveying practice using metric chains, the length of a normal chord is typically taken as 20 m (or 1 chain length) ┬╖ Any chord shorter than this standard length at the beginning or end of the curve is designated as a sub-chord.
In route surveying, a normal chord (also known as a full chord) is defined as the standard full chain length chord between two consecutive main stations along a circular curve ┬╖ In standard Indian surveying practice using metric chains, the length of a normal chord is typically taken as 20 m (or 1 chain length) ┬╖ Any chord shorter than this standard length at the beginning or end of the curve is designated as a sub-chord.
C=20┬аm тАФ standard length of a normal chord in 20 m metric chaining
R=D1146тАЛ тАФ relation between radius (R) and degree of curve (D) for a 20 m arc/chord
╬┤=28.65├ЧRcтАЛ┬аdegrees тАФ deflection angle for a chord of length c
When setting out circular curves in the field, main stations are established at regular chainage intervals corresponding to 1 full metric chain ┬╖ The chord joining two successive full stations is termed a normal chord ┬╖ Because the tangent point usually falls at an intermediate chainage rather than an exact full station, initial and final shorter chords called sub-chords are required to complete the alignment.
A normal chord connects two successive full stations on a curve and equals 1 full chain length (20 m in standard metric practice).
Chords at the beginning (initial) and end (final) of a curve that are shorter than 20 m are called sub-chords.
The total length of a circular curve consists of an initial sub-chord, multiple normal chords, and a final sub-chord.
Setting out simple, compound, and reverse circular curves on roads and railways using Rankine's deflection angle method.
Computing curve elements and station chainages during highway and transit route alignment surveys.
Option A (10 m) represents half-chain intervals often used for setting out sharp curves to minimize the discrepancy between arc and chord lengths.
Option B (15 m) is an arbitrary chord length and not a standard metric chain unit in Indian surveying practice.
Option D (25 m) is occasionally used in international practice with non-metric units, but standard Indian IS code specifies 20 m (or 30 m) chains.
C is correct тАФ The standard length of a normal chord in metric route surveying is 20 m, which corresponds to one full metric chain length.
Remember that for a 20 m chain, R=D1146тАЛ, whereas for a 30 m chain, R=D1719тАЛ. Exam questions frequently swap these constants based on the standard chord length used.