Prestressed vs Reinforced Concrete: Key Structural Differences

Characteristic Features of Prestressed Concrete

The primary difference compared to reinforced concrete is the ability to resist higher loads before cracking. The compression force introduced into the concrete via prestressing ensures that, once cracks occur, they are less developed and have a smaller width under the same level of external load.

Furthermore, prestressed elements exhibit higher stiffness. When cracks form, the stiffness of a reinforced element decreases significantly; however, a prestressed element remains stiffer, resulting in reduced elongation or deflection under bending.

Key advantages include:

• Reduced cross-section depth: Lowers self-weight, saves material, and enables longer spans.
• High toughness and ductility: Requires significantly more energy to cause structural failure.
• Force control: Prestressing allows for the active control of internal force distribution within the structure.

Properties of Concrete for Prestressed Structures

A distinctive feature of prestressed concrete is that the active reinforcement is subjected to stress before the structural member experiences planned service loads. There are two primary methods:

• Pre-tensioning: Reinforcement is tensioned before the concrete is poured. Stress transfer occurs through direct bond contact between the hardened concrete and the reinforcement once the tendons are cut.
• Post-tensioning: Reinforcement is tensioned after the concrete has hardened. In non-adherent systems, tendons are placed in ducts and anchored at the ends, meaning there is no bond between the steel and the concrete along the length of the member.

Properties of Prestressing Steel

Steel used in prestressed applications must be of high quality and possess the following attributes:

1. High strength: To withstand significant tension.
2. Adequate ductility: To ensure structural safety.
3. Bendability: Required at harping points and near anchorages.
4. High bond: Essential for pre-tensioned members.
5. Low relaxation: To minimize long-term prestress losses.
6. Corrosion resistance: To ensure durability.