Question

The diameter of a concrete flag post varies from 240 mm at base to 120 mm at top as shown in Fig.  The height of the post is 10 m. If the post is subjected to a horizontal force of 600 N at top, find the section at which stress is maximum. Find its value also.

Answer 1

Consider a section y metres from top. Diameter at this section is

At this section, moment is given by 

M = 600 y N-m 

= 600000 y N-mm. 

Equating moment of resistance to moment at the section, we get 

f Z = M 

where f is extreme fibre stress

Stress at this section f is given by