How a girder is being prestressed while fabrication? Explain the components/materials used during the prestressing?

To prestress a girder during fabrication, the following steps are typically followed:

1. Design: The girder is first designed, taking into consideration the required strength and load-bearing capacity. The design includes determining the prestressing force required and the location of the prestressing tendons.

2. Fabrication: The girder is fabricated using high-strength concrete or steel. The fabrication process involves casting the girder in a precast yard or on-site, depending on the project requirements.

3. Prestressing tendons: Prestressing tendons, typically made of high-strength steel, are placed in the girder before the concrete is poured. These tendons are tensioned using hydraulic jacks to apply the desired prestressing force.

4. Anchorage: The prestressing tendons are anchored at the ends of the girder using specialized anchorage systems. These systems ensure that the prestressing force is transferred to the girder effectively and securely.

5. Stressing: Once the concrete has gained sufficient strength, the prestressing tendons are stressed using hydraulic jacks. This process involves applying a force to the tendons, which transfers the compressive stress to the girder, resulting in prestressing.

6. Release: After the desired prestressing force is achieved, the hydraulic jacks are released, and the tendons are locked in place using wedges or other anchoring devices. This ensures that the prestressing force is maintained in the girder.

During the prestressing process, the following components and materials are used:

1. Prestressing tendons: These are high-strength steel cables or bars that provide the tensile force required to prestress the girder.

2. Anchorage systems: These are specialized devices used to anchor the prestressing tendons at the ends of the girder. They ensure the transfer of the prestressing force to the girder.

3. Hydraulic jacks: These are used to apply the force required to tension the prestressing tendons. They are essential for achieving the desired prestressing force.

4. Concrete: High-strength concrete is used to cast the girder. It provides the compressive strength required to resist the prestressing force and support the load.

5. Wedges or anchoring devices: These are used to lock the prestressing tendons in place once the desired prestressing force is achieved. They prevent the tendons from slipping or losing their tension.

Overall, the prestressing process involves carefully designing the girder, using high-strength materials, and applying tension to the prestressing tendons to create a strong and durable structure.