Setting out a simple circular curve by offset method

Theory

This method is generally used for setting out small curves as in case of the street bents.

Instrument required

1.      30 Meter chain

2.    Tape

3.    Arrows

4.    Pegs

5.     Ranging rods

6.    Prismatic compass

Procedure

• In this method the first step was locate the points T₁ and T₂ i.e. point of curve and point of tangent. There chainage were marked from the origin.

• The lengths of such cord and normal cords three decided.

• The length of long cord was divided into an even number of equal part.

•  The offsets at each point then determine by the formula

•   ­ (R – O₀) and the offsets where mark on the ground with the help of cross staff since the curve was cymetrical at both side of the on middle ordinate the offsets for the left hand half of the curve were the same both the sides those for right hand half.

•  Thus we got the positions of required point on the curve. Thus the curve was set.

Diagram

Result

Here chain and tape used for setting out the curve. This method used because the curve was short and high degree of accuracy was not required.