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Pre-stressed Concrete how does it apply to reinforced concrete

What is Prestressed Concrete?

What is prestressed concrete how does it apply to reinforced concrete?

We all know that concrete is strong in compression and weak in tension. This is reason for providing reinforcement (in the form of steel bars) to resist tension/tensile force acting on beams/columns/slabs etcetera.

RC structures under service load undergoes deflection causing the bottom of the beam (tensile zone) to elongate, causing cracks. Steel bars are provided to limit the crack widths and resist the tensile force which the concrete lacks.

Here, the rebar acts as ‘passive reinforcement’. Rebars (steel reinforcement) provided at the bottom of the bar, does not carry any forces until the concrete has already deflected enough to crack.

How it is used?

This is where prestressing comes into action. The principle behind prestressed concrete is that compressive stresses induced by high-strength steel tendons in a concrete member before loads are applied will balance the tensile stresses imposed in the member during service.

Simply, Permanent pre-compression is produced in the areas subjected to tension using high tensile strength steel wires or alloys. Now, a portion of tensile stress is counteracted, thereby reducing the cross-sectional area of steel reinforcement.

As  result, the concrete does not crack because the pre-stressing has reduced the tensile stress in the section below cracking stress. hence coA prestressed concrete structure is different from a conventional reinforced concrete structure due to the application of an initial load on the structure prior to its use.

The initial load or prestress is applied to enable the structure to counteract the stresses arising during its service period.Prestressing of structures was introduced in late nineteenth century. The concept of prestressing existed before the applications in concrete is treated as a elastic material.

Reinforced concrete vs. prestressed concrete

What is the difference between conventional reinforced concrete and prestressed concrete?

 In prestressed concrete, internal stresses are introduced by compressing the concrete so that the tensile stresses resulting from service loads can be counteracted to a desired degree. The prestress is introduced by tensioning the tendons. The presence of the prestress enables the concrete to carry higher loads without cracking. With prestressed concrete, the engineer can also design longer spans using the same depth beam.