Question

According to thin cylinder theory, the volume of concrete required for an arch dam would be minimum if the central angle is ____________

(a) 130° 34’

(b) 133° 34’

(c) 143° 34’

(d) 153° 34’

The question was asked in my homework.

My doubt is from Arch Dams topic in division Arch and Buttress Dams of Irrigation Engineering

Answer 1

Right option is (b) 133° 34’

Explanation: The most economical central angle is equal to 133°-34’ and such an angle can be adopted only at one place in constant radius arch dam as there is considerable variation with height due to narrow V-shape of the valley. It is therefore considered to keep the economical angle of 133°-34’ at about mid-height for a minimum value of concrete.