Question

why in actule can not reach to balance rinforcemen in beam?

Answer 1

In RCC beams, steel takes tension and concrete takes compression.

In balanced section, both concrete and steel reaches its maxium stress value simultaneously and fails simultaneously.

In general most of the singly reinforced beams designed as under reinforced beams. In under reinforced beams, the stress in steel reaches its maximum value before concrete and fails before concrete. The steel failure in RCC beams is ductile failure which shows some cracks on the beam as warning sign so that we can take care of ourselves before collapse occurs. In case of balanced sections this flexibility not occur and whole beam collapse suddenly causing damage to living people. One more thing, in under reinforced sections engineers provide less steel that required for balanced section, hence save in material and money.

So for safety and economy purposes, engineers design the beams such that actual reinforcement always less than balanced reinforcement.