Setting out of curve (Survey)

AHEMEDABAD INSTITUTE
OF TECHNOLOGY
SEMINAR
Setting out of curve

CIVIL ENGINEERING (3rd sem)B.E
SUBJECT: SURVEYING
Submitted by:
 Patel Bhavik
 Patel Parth
 Bhavsar Zalak
 Dodia Margi
 Limbhachya setu
 Patel Mitul
 Patel Garvish

Methods of setting out simple
circular curve
Based on the instruments used in setting
out the curves on the ground there are two
methods:
1) Linear method
2) Angular method

Linear Method
 In these methods only tape or chain is used
for setting out the curve . Angle measuring
instrument are not used.
Main linear methods are
 By offsets from the long chord.
 By successive bisection of arcs.
 By offsets from the tangents.
 By offsets from chords produced.

By offsets from the long chord

R = Radius of the curve
0o = Mid ordinate
0x = ordinate at distance x from the mid point
of the chord
T1 and T2 = Tangent point
0o = R -- 𝑅2 − (
𝐿
2
)2
0x = (𝑅2 −𝑥2 ) –(R – 0o)

By successive bisection of arcs

 Join the tangent points T1,T2 and bisect the
long chord at D.
 Erect perpendicular DC at D equal to the
mid ordinate.
 Join T1C and T2C and bisect them at D1
and D2 respectively.
 D1 & D@ set out perpendicular offsets
C1D1=C2D2=(1-- cos
∆
4
) and obtain points
C1 and C2 on the curve.

By offsets from the tangents
 The offsets from the tangents can be of
two types
1) Radial offsets
2) Perpendicular offsets

1) Radial offsets
0X = 𝑅2 + 𝑥2 -- R

2) Perpendicular offsets
Ox = R -- 𝑅2 − 𝑥2

By offsets from chords produced

01 =
𝐶12
2𝑅
02 =
𝐶12
2𝑅
(C1 + CL)
03 = 04 = 𝑂 𝑛−1 =
𝐶𝑙2
2𝑅
(2CL) =
𝐶𝐿2
𝑅
0n =
𝐶′
2𝑅
(CL + 𝐶′)

Angular Method
 This methods are used when the length of
curve is large.
The Angular methods are:
1) Rankine method of tangential angles
2) Two theodolite method
3) Tacheometric method

Rankine method of tangential angles
 “A deflection angle to any point on the curve is the angle at
p.c. between the back tangent and the chord from p.c. to that
point.”

 Set out 𝑇1 and 𝑇2.
 Set the theodolite 𝑇1.
 With both the plates clamped to zero, direct the
theodolite to bisect the point of intersection.
 Release the upper clamp screw and set angle ∆1 o the
vernier.
 With zero end of the tape pointed at T1 and an narrow
held at a distance T1A=C1 swing the tape around T1
till the arrow is bisected by the cross hairs.
 Release the upper plate and set the second deflection
angle ∆2 on the vernier so that the line of sight is
directed along T1B.
 With the zero end of the tape pinned at Avand an arrow
held at a distance AB = C2 swing the tape around A till
the narrow is bisected by the cross hairs.
 Repeat the steps 6,7 till the last point T2 is reached.
 Join the points T1,A,B,C….T2

 In this method two theodolites are used one
at P.C and the other at P<T.
 In this method tape/chain is not required.
This method used when the ground is
unsuitable for chaining.
 < V𝑇1 A = ∆1= Deflection angle for A.
 < A𝑇2T is the angle subtended by the chord
T1A in the opposite segment.
 (A𝑇2 𝑇2 =<VT1A=∆1)
 <V𝑇1B = ∆2 = <𝑇1 𝑇2 B

 Set the tacheometer at 𝑇1 and sight the
point of intersection when the reading is
zero.
 Set the deflection angle ∆1 on the vernier,
thus directing the line of sight along 𝑇1A.
 Direct the staff man to move in the direction
𝑇1A till the calculated staff intercept 𝑆1 is
obtained. The staff is generally held vertical.
First point A is fixed.
 Set the deflection angle ∆2 directing the line
of sight along 𝑇1B. Move the staff backward
or forward untill the staff intercept 𝑆2is
obtained thus fixing the point B.
 Same other points are fixed.

Setting out of curve (Survey)

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