Understanding Key Components in Prestressed Concrete Construction

In prestressed concrete construction, it is crucial to understand the function and characteristics of each component to ensure the quality of the project. Today, we will provide a detailed overview of common prestressing components and their roles.

1. Corrugated Pipes

In post-tensioned bonded prestressed concrete structures or components, the ducts for the prestressing tendons are typically formed using rigid or semi-rigid pipes embedded in the concrete, or by methods such as steel pipe extraction, rubber pipe extraction, and metal expansion joint extraction. Corrugated pipes can be categorized based on material into metal and plastic types; by cross-sectional shape into round and flat shapes; and by radial stiffness into standard and reinforced types. Their primary role is to ensure the stability of the ducts and maintain their original shape under the weight of the poured concrete, thus facilitating the transfer of bonding stresses.

2. Prestressing Tendons

Prestressing tendons are usually composed of single or bundled steel wires, steel strands, or rebar. They can be categorized based on the construction method into bonded and unbonded prestressing tendons. Bonded prestressing involves leaving ducts in the concrete component or structure, pouring concrete, curing it, threading the prestressing tendons into the ducts, and then tensioning and anchoring them once the concrete reaches the required strength, followed by grout filling and anchoring. Unbonded prestressing tendons, however, do not come into direct contact with the concrete and are protected by a corrosion-resistant layer and an outer sheath.

3. Bearing Plates

Bearing plates are embedded components used in prestressing tensioning operations. Their primary function is to transfer and distribute pressure, reducing the concentration of stresses in the concrete and preventing cracking and damage during prestressing. The design of bearing plates helps to effectively distribute the load area of the anchoring device, enhancing structural stability.

4. Spiral Reinforcement

The role of spiral reinforcement is to enhance the compressive strength of the local concrete beneath the anchor and to prevent cracking or crushing of the concrete due to concentrated stresses during the tensioning of prestressing tendons. Spiral reinforcement is typically placed behind the bearing plates to improve compressive strength.

5. Anchors (Working Anchors)

Anchors can be divided into two main types:

Tension End Anchors: Installed at the end of prestressing tendons and designed to maintain anchorage during the tensioning process. Common types include clip-type anchors for tensioning steel strands (YJM), steel conical anchors for high-strength steel wires (GZM), head anchors for post-tensioning high-strength steel wires (DM), nut anchors for precision-rolled threaded bars (YGM), and cold-cast head anchors for multi-strand parallel wire bundles (LZM).

Fixed End Anchors: Installed at the end of prestressing tendons, typically embedded in concrete, and not used for tensioning. Also known as compression anchors or P-anchors.

6. Limit Plates

Limit plates play a role in fixing the anchor clips during prestressing tensioning. An appropriate limit distance (the depth of the limit plate slot) helps to minimize the retraction of the anchor. The simplest method to measure retraction is to subtract the exposed portion of the anchor clip after tensioning from the depth of the limit plate slot.