why do we prefer the under reinforcement section over a balanced or over reinforcement section?

Summary:

Under-reinforced sections in a structure are preferred because they allow for a greater degree of ductility, which means the structure is better able to withstand deformation and maintain its integrity during a load-bearing event, such as an earthquake or high winds. An under-reinforced section will also typically have a greater load-carrying capacity than an over-reinforced section, as the reinforcement can only be utilized up to a certain point before it becomes ineffective. Additionally, over-reinforced sections can lead to brittle failure, where the structure breaks suddenly and completely, rather than slowly and gradually deforming. This can lead to a higher risk of collapse and injury.

why do we prefer under reinforcement section over balanced or over reinforcement section?

When a structure is under-reinforced, the concrete and steel reinforcement work together to absorb and distribute the loads placed on the structure. The concrete will begin to crack and deform, allowing the steel reinforcement to take on more of the load. This process is known as ductile failure, and it allows the structure to deform and bend without breaking. This type of failure is considered safer than brittle failure, which occurs when a structure is over-reinforced and the concrete is not able to crack and deform. Instead, the steel reinforcement will take on all of the load and the structure will break suddenly and completely, leading to a higher risk of collapse and injury.

In addition to the safety benefits, an under-reinforced section also typically has a greater load-carrying capacity than an over-reinforced section. This is because the reinforcement can only be utilized up to a certain point before it becomes ineffective. By not over-reinforcing a structure, engineers can ensure that the structure is able to withstand the loads it was designed for, without wasting materials or increasing costs.

In summary, under-reinforcement is preferred because it leads to a more ductile failure mode, which is safer for the structure and for people. Additionally, under-reinforced sections typically have a greater load-carrying capacity and over-reinforcing can lead to brittle failure and wasting materials.