Construction of Parabola by Offset Method

CONSTRUCTION OF PARABOLA BY OFFSET METHOD

Data known : 

1. Base 

2. Rise

Example 10: Construct a parabola of base (span) 8m and rise 5m by offset method.

Procedure:

1. Full scale cannot be followed to draw with given dimensions, 8m and 5m. Hence, a suitable reduced scale to be followed.

2. Draw a rectangle ABCD of length 80mm and height 50mm and locate the mid point of AB at O.

3. Draw bisector through O to cut the edge CD at E. 

4. Divide ED into any number of equal parts (say 4) and name the parts as 1, 2 and 3 from D.  

5. Draw vertical lines through 1, 2 and 3 parallel to OE to mark the offsets.

6. To measure the offset through the point 1.

Distance E-1 is 3/4 of the length ED. Hence, offset is equal to (3/4)2 of axis ie., (3/4)2 × EO = (3/4)2 × 50mm = 28.12mm. Measure 28.12 mm along the vertical line passing through 1 to get P1.

7. Similarly locate the points P2 and P3 through 2 and 3 respectively by computing respective offsets.

8. Draw a smooth curve joining the points A, P1, P2, P3 and E which is half of the parabola. 

9. Repeating the same procedure on the right side of axis, the other half of parabola is constructed.