Concrete Construction Introduction

Introduction of prestressing construction

Prestressing is applied to improve the performance of structures during use by pre-applying stress to the structure during construction. This pre-applied stress can fully or partially counteract the tensile stress caused by loads during the service life of the structure, thereby preventing structural failure. Prestressed concrete structures are those in which stress is applied to the concrete before it is subjected to loads. This pre-applied stress induces compressive stress in the tensile zones of the concrete when external loads are applied. This counteracts or reduces the tensile stress caused by external loads, ensuring that the structure does not crack or cracks later under normal service conditions.

Classification of prestressing tensioning construction

Pre-Tensioning

Process: Before casting concrete, steel tendons (PC strands) are tensioned in a mold. The tendons are anchored at each end of the mold and stressed to the desired level of pre-tension.

Concrete Casting: While maintaining the tension in the tendons, concrete is poured into the mold. Once the concrete hardens, the tensioning devices are released, and the pre-stress is transferred to the concrete through bond.

Application: Pre-tensioning is typically used for precast concrete elements, such as bridge girders, hollow-core slabs, and other prefabricated components.

Post-Tensioning

Process: After the concrete element has been cast and gained sufficient strength, steel tendons are threaded through ducts or voids within the element, and anchorages are installed at each end.

Applying Pre-Stress: Tension is applied to the tendons using jacking equipment, and the tendons are then anchored in place.

Grouting: To protect the tendons and enhance the bond, grout or other filling materials are injected into the ducts.

Application: Post-tensioning is commonly used in cast-in-place concrete structures, such as large bridges, slabs, and long-span structures.