As one of the development trends of modern concrete, prestressed concrete is more and more widely used in commercial buildings. Prestressed concrete is characterized by large span, light weight and saving building materials.
Materials, saving building height, improving building and structural functions and other outstanding advantages can effectively solve the large space use requirements that were difficult to solve in previous high-rise buildings and improve the comprehensive economic benefits of buildings.
Prestressed concrete; Theoretical principle; App application
1 Introduction
After half a century's development, prestressed concrete technology has been widely used in the world.
A new technology used all over the world. The range and quantity of prestress technology have become the standard of measurement.
One of the important symbols of national building technology level. It is transformed from single-storey and multi-storey houses in the past.
The application of roads, railway bridges, sleepers, poles, pressure pipes, reservoirs and water towers has been extended to high-rise buildings.
Pressure on buildings, underground buildings, towering structures, Shui Mu structures, offshore structures, airport runways and nuclear power plants.
Containers and large tonnage ships. , and has been more and more accepted by the majority of engineering and technical personnel. place
Refers to the prestressed concrete structure, that is, before the load is applied, pressure is applied to the members so that when the load is applied,
In the process of concrete structure, there is already compressive stress in the tensile area of cross section. Because the cross section is preloaded
Compressive stress can completely or partially eliminate tensile stress caused by load, but concrete can't.
The reappearance of cracks or at least delay the appearance of cracks. Therefore, prestressed concrete structures can significantly
Improve the crack resistance and section stiffness of members. At the same time, it also manufactures high-strength steel bars and high-strength concrete.
The application of soil greatly improves the bearing capacity of members.
2 the development status of prestressed concrete technology in China
2. 1 raw materials have good performance.
Prestressed steel has changed the past phenomenon of low strength, miscellaneous varieties, unstable quality and short supply.
Become a high-efficiency prestressed steel bar with gradually improved strength, complete varieties and specifications, excellent quality and meeting the requirements.
Technical requirements such as design and construction.
2.2 Improvement of key technologies
The development and application of jack, anchorage and fixture for large tonnage tensioning have solved this problem well.
The key technology in prestressed construction technology ensures the application and development of prestressed technology.
2.3 The specifications and procedures have been basically matched.
Code for design of concrete structures, technical code for particle-free prestressed concrete structures and pre-construction
Stress bar anchorage, fixture and connector and other national product standards and application technical regulations, as well as "none"
Many countries, such as special anti-corrosion grease for bonding prestressed steel bars, hydraulic jack for prestress, etc.
Domestic and local technical regulations and product standards have also been basically put in place. Meet the needs of the project, make
All kinds of prestress techniques have rules to follow.
2.4 The prestressed concrete structure with international advanced level has been built.
With the application of prestressed concrete technology, a number of prestressed concrete with international advanced level have been built in China.
Force concrete engineering. For example, the Nanjing International Exhibition Center project has the largest column grid size (column grid size
25m×27m)； The main building of Guangdong International Hotel with the largest number of floors (63rd floor); The highest Qingdao China Bank University.
Building (24 1m), which shows that China's prestressed concrete technology has reached a fairly high level.
Level.
3 prestressed concrete prestressing method
The production methods of prestressed concrete members include pre-tensioning method and post-tensioning method.
3. 1 pretensioning method
Before concrete pouring, prestressed tendons composed of steel wires, stranded wires or steel bars are tensioned.
To the specified stress, anchor on the piers at both ends of the pedestal with anchors, and then install the formwork and structural steel.
Steel and parts, and then pouring concrete and curing. When the concrete reaches the specified strength, put
Loosen the prestressed tendons of the piers at both ends, and transfer the tension in the prestressed tendons to the concrete through the bonding force.
So as to generate pre-compression stress. The pretensioning method has more advantages with long pedestals, the longest of which is more than 100.
Rice, so it is sometimes called long line method.
3.2 post-tensioning method
The method of pouring components first and then directly prestressing them. The usual practice is
First place casing, structural reinforcement and post-tensioned prestressed reinforcement, and then install formwork and grouting.
Build concrete. Prestressed tendons can be inserted into the casing first or later. When the concrete reaches the strength,
The prestressed tendons are stretched to the required stress by jack and anchored at both ends of the beam, and the preloading stress is passed.
The anchorage at both ends is transferred to the concrete of the member. In order to protect prestressed steel bars from corrosion and restore prestress
The cohesive force between steel bar and concrete, and the gap between prestressed steel bar and casing must be filled with cement slurry.
Real. Cement slurry not only plays an anti-corrosion role, but also helps to restore the bond between prestressed tendons and concrete.
In order to facilitate construction connection, anticorrosive materials can sometimes be coated on the surface of prestressed tendons.
Unbonded post-tensioned tendons wrapped in plastic casing or oil paper.
4. Engineering application of prestress technology
4. 1 Application of Prestressed Concrete in High-rise Structure
In recent years, great progress has been made in the application of prestressed concrete in high-rise building structures, and
And achieved good economic benefits, mainly reflected in: unbonded prestressed concrete slab.
The prestressed flat beam is used in the floor of high-rise building, which has the advantages of reducing the height, saving steel and simplifying the mold.
Board, speed up the construction and other significant effects; Application of prestressed concrete facing thermal insulation composite wallboard, full
Sufficient diversity and durability of building exterior wall decoration, but also in thermal insulation, energy saving, industrial production,
Rapid construction and other aspects have played a huge advantage; Installation of precast prestressed members is combined with cast-in-place construction.
There are more and more integrated high-rise building structures; With the development of prestressed construction technology and durability technology
Perfect, some new structures that are more suitable for prestressed concrete will be greatly developed. such as
The emergence of suspended buildings.
4.2 Application of Prestressing Technology in Assembled Integral Structure
Because prefabricated components have many advantages of factory-scale production, such as quality control level.
High durability, high template turnover rate, low loss, etc. And make it have better technical and economic benefits.
Indicators. Therefore, the modern prefabricated integral structure is being built, which combines precast prestressed members and cast-in-place members.
The proportion of application in architecture is also increasing, which is manifested in long-span hollow floors and industrial buildings.
Roof trusses, crane beams, roof panels, long-span prestressed hollow slabs, T-shaped slabs in multi-storey and high-rise buildings,
Cast-in-situ joint of large prestressed wallboard and precast beam slab or precast beam, slab and column.
Various assembled integral building structures, etc.
5 concluding remarks
In order to adapt to the development of China's economy, the application scope of prestressed concrete structures will be wider.
Wide, so we should strengthen scientific research and improve the technical level of prestress. Compared with developed countries
In contrast, the research on prestressed concrete engineering in China is relatively backward. The separation of design and construction is also a shadow.
One of the factors affecting the rapid development of prestressed concrete structures in China. Therefore, it is necessary to establish a large-scale
A powerful prestressed concrete engineering company undertakes large-scale prestressed concrete projects and undertakes
Negative new technology development and research, and do a good job with the design and construction, in order to improve China's pre-.
Technical level of pressure.
References:
[1] Yang Zongfang, Fang Xianhe. Modern prestressed concrete buildings. Beijing: Construction industry in China.
News, 1993
[2] Wang Hua. Application of 10 new technology in construction industry. Nanjing: Jiangsu Science and Technology Press.
Society, 2002
[3] Wu Yuannai et al. 10 New technologies in the construction industry and their applications. Beijing: Construction industry in China.
Press, 200 1