Balanced Reinforced Section :-
Reinforced concrete beam sections in which the tension steel also reaches yield strain simultaneously as the concrete reaches the failure strain in bending are called balanced sections.
Over Reinforced Section:-
Reinforced concrete beam sections in which the failure strain in concrete is reached earlier than the yield strain of steel is reached, are called over-reinforced sections .
If such beam is designed and loaded to full capacity then the steel in tension zone will not yield much before the concrete reaches its ultimate strain of 0.0035. This due to little yielding of steel the deflection and cracking of beam does not occur and does not give enough warning prior to failure. Failures in such sections are all of a sudden.
This type of design is not recommended in practice of beam design.
Under Reinforced Section :-
Reinforced concrete beam sections in which the steel reaches yield strain at loads lower than the load at which the concrete reaches failure strain are called Under-reinforced sections.
Every singly reinforced beam should be designed as under-reinforced sections because this section gives enough warning before failure.