What are the applications of prestressed concrete in engineering?

China began to promote prestressed concrete in 1956. In the 1950s, cold-drawn steel bars were primarily used as prestressing tendons to manufacture components for industrial village buildings such as precast prestressed concrete roof trusses and crane beams. In the 1970s, small and medium-sized prestressed concrete components reinforced with cold-drawn low-carbon steel wires began to be widely used in civil buildings. Since the 1980s, prestressed concrete has been widely used in modern projects such as large public buildings, high-rise and super-high-rise buildings, long-span bridges, and multi-story industrial plants. After more than 50 years of efforts in research, China has developed a unique system in areas such as the design theory, calculation methods, component series, structural systems, tensioning and anchoring systems, prestressing techniques, as well as prestressed bars and concrete materials for prestressed concrete ； Rich experience has been accumulated in the construction technology and management of prestressed concrete.

Due to their small cross-section, high stiffness, good crack resistance, and durability, prestressed concrete structures are widely used in the field of civil engineering around the world. In recent years, the emergence of high-strength steel and high-strength concrete has promoted the development of prestressed concrete structures, and further contributed to the refinement and improvement of prestressed concrete construction techniques.

Characteristics of prestressed concrete: The ultimate tensile strain of ordinary reinforced concrete members is only 0.0001~0.00015. When the concrete of a component does not crack under tension, the stress in the tensile steel bars within that component is only 20–30 N/mm2 ； Even in members where cracks are permitted, due to the limitation imposed by the crack width, the stress on the tensile steel bars only reaches 150–200 N/mm2, preventing the tensile strength of the bars from being fully utilized. Prestressed concrete is an effective method to solve this problem, that is, by applying prestress to the concrete in the tensile zone of the member in advance, before the member is subjected to external loads. When tensile stresses are generated in a member under external loads during its service life, the pre-compression stress must first be offsetted. This delays the appearance of cracks in the concrete and also limits their progression, thereby improving the crack resistance and stiffness of the member. The method of applying prestress to the tensile zone of concrete members involves tensioning the prestressed steel bars in that zone; through these steel bars or anchors, the elastic contraction force of the prestressed bars is transmitted to the concrete member, thereby generating prestress. Reinforcement bars are generally processed in a reinforcement bar workshop or a processing shed at the construction site, and then transported to the site for installation or binding. The steel bar processing process depends on the type of finished product; common processing methods include cold drawing, cold extrusion, straightening, cutting, heading, bending, welding, and tying.