Difference Between R.C.C and Prestressed Concrete (PSC) Structures

Reinforced concrete and prestressed concrete are two different types of concrete structural design that varies in how they achieve strength and how they carry external loads. In order to understand prestressed concrete, you will have to clearly understand the basic concepts of R.C.C.

R.C.C is a concrete reinforced with steel rebars in order to take tensile strength, as concrete takes the compressive strength. While PSC is a type of concrete that uses tendons to induce stress in the concrete, like a reserve energy from outside to face the external load. 

Here, we will clearly explain the difference between Reinforced concrete and prestressed concrete in detail.

Difference Between Reinforced Concrete (RCC) and Prestressed Concrete (PSC)

1. Cross-sectional area contributing to compression is HIGH for prestressed concrete compared to R.C.C concrete. 

If you consider the cross-sectional view of an R.C.C beam with rebars at the bottom and clearly showing the neutral axis or the neutral fibre (NA). We know when the beam bends under the load say w per m, the top portion is in compression above the neutral axis and bottom portion is in tension (below the neutral axis), this is concluded based on the real effects of load on the beam. Where the top fibres contract and the bottom fibres expands. 

As the bottom portion is subjected to more tension, and the concrete we know is weak in tension, we introduce steel reinforcement in this area. So to summarise, the top portion of the cross-section of the R.C.C beam only contributes to the compression strength (C). Below portion, is only for Tension (T). The purpose of concrete below neutral axis is mainly to hold the rebars upright as the layout. 

Now consider  prestressed concrete beam with neutral axis N-A. Here, before putting the beam to service load, we induce compressive stresses below the NA area, through tendons. So bottom portion is full of compression. Under service loads, w per m, top and bottom portion of the cross-section contributes to compressive strength. 

This is why, cross-sectional area contributing to compression is HIGH for prestressed concrete compared to R.C.C concrete. 

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2. R.C.C need large cross-sectional dimension than PSC to carry a certain amount of load

As explained before, to carry a specific load, only a portion of cross-section is involved in load bearing. But PSC puts the complete cross-section for load carrying. 

So to carry a specific load value, the R.C.C demands large cross-section compared to PSC. 

3. R.C.C Structures are prone to crack formation compared to PSC

We know that R.C.C structures are designed such a way that steel rebars fails first. When steel rebars yield first, the surrounding concrete that binds it together starts to separate. Yes, I am talking about the concrete portion below the neutral axis of the r.cc beam that do not have any responsibility to contribute strength, but only to hold the bars together. So, when the rebars separate, the concrete loose bond and cracks are formed at the bottom layers, also called as tension cracks. 

In the case of prestressed concrete (PSC), the situation is different. Before the external load is applied, the concrete member is already compressed internally by the action of prestressing tendons. These tendons apply a pre-compressive force to the concrete, which counteracts the tensile stresses that develop under service loads.

Because of this pre-compression, the entire cross-section of the beam remains mostly in compression even after the external load is applied. As a result, tensile stresses are significantly reduced or completely eliminated, preventing the formation of tension cracks that are common in R.C.C structures.

In short:

• R.C.C beams develop cracks because the steel reinforcement resists tension only after the concrete in that zone cracks.
• P.S.C beams, on the other hand, are designed to keep the concrete in compression throughout its service life, thereby minimizing or eliminating cracks.

4. Deflection in R.C.C is high while, it is counterbalanced in PSC

In Reinforced Cement Concrete (R.C.C) structures, deflection is generally higher because the concrete in the tension zone cracks early under loading. Once cracks form, the effective stiffness of the member decreases, allowing greater bending and downward deflection. The steel reinforcement alone resists the tensile stresses, while the cracked concrete contributes very little.

In contrast, Prestressed Concrete (P.S.C) members are designed so that initial compressive stresses are introduced before the actual service load is applied. These pre-compressive forces counteract the tensile stresses that develop under loading. As a result, the net deflection is significantly reduced, and in some cases, the member may even show upward camber initially due to prestressing.

5.R.C.C required additional shear reinforcement compared to PSC

When a beam carries load, diagonal shear cracks develop in the R.C.C portion near supports or where shear forces are high. Since the concrete’s tensile strength is low, it cannot resist much of the diagonal tension caused by shear. Hence, shear reinforcement (stirrups) is required in R.C.C to:

• Resist the diagonal tension.
• Hold the cracked sections together.
• Prevent sudden shear failure. 

In pre-stressed concrete, the compressive stresses induced by pre-stressing reduce or even eliminate tensile stresses in the concrete under service loads. This compression delays the formation of cracks, and as a result:

• The section remains mostly uncracked under working loads.
• The shear capacity of concrete itself increases.

Therefore, less additional shear reinforcement is needed in P.S.C compared to R.C.C.

6. R.C.C does not require high grade steel or cement compared to PSC

In R.C.C structures, we generally use normal-grade materials like ordinary Portland cement (OPC 33 or 43 grade) and mild or medium-strength steel such as Fe415 or Fe500. This is because the stresses developed in R.C.C are much lower compared to the ultimate strength of the materials.

The concrete mainly handles compression, and the steel handles tension — but both work well even with standard-grade materials. Since there’s no pre-stressing involved, the steel is not required to be stretched or tensioned to very high limits, which makes the use of normal grades both economical and sufficient for safety.

However, in P.S.C , the situation is entirely different. Here, the concrete is pre-compressed using high-strength steel tendons, which means both materials must withstand very high internal stresses before the actual external load even comes into play. 

As a result, high-grade cement (usually 53 grade or higher) is used to gain the required early strength, and high-tensile steel wires or strands (with strengths around 1500–1800 MPa) are essential to maintain the pre-stress. So, while R.C.C can be constructed using standard materials, P.S.C demands high-grade steel and cement to perform effectively and safely.

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