एकली प्रबलित बीम (singly reinforced beam) की तुलना में दोहरी प्रबलित बीम (doubly reinforced beam) को किस स्थिति में प्राथमिकता दी जाती है?

According to IS 456:2000, the minimum percentage of high yield strength deformed (HYSD) bars in an R.C. slab compared with total gross concrete area is:

As per standard civil engineering provisions (IS 456), the nominal clear cover (in mm) to main reinforcement bars in footings, columns, beams, and slabs are respectively: