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1、Prestressed Concrete Technology
提綱：
摘要：預(yù)應(yīng)力混凝土的定義
正文：預(yù)應(yīng)力混凝土的應(yīng)用、實(shí)例應(yīng)用
討論：預(yù)應(yīng)力混凝土的優(yōu)點(diǎn)和缺點(diǎn)
總結(jié)：預(yù)應(yīng)力混凝土的發(fā)展的前景
Introduction
Prestressed concrete and reinforced concrete in principle are clearly different. In the design of the reinforced concrete beams, regardless of the concrete can be assumed
2、 that the tensile strength, for bending moment of tension is caused by reinforced to resist, the tension is through between reinforcement and concrete bonding and passed to the steel. For large scale craze and deformation for, although the high strength concrete has good bonding, to a great extent c
3、an restore; But in the concrete and steel bonding between poor ordinary concrete, is in fact cant recover. On the other hand, in the prestressed concrete, the purpose of prestressed reinforced by rapping or through the special is the anchorage to exert a force concrete, so all can have the function
4、of concrete structure. Requirements of prestressed steel is used to produce active component in advance to add load, and cracking and deformation in larger extent can be restored.
Abstract
In order to avoid reinforced concrete structure of the premature fracture, make full use of high strength ste
5、el and high strength concrete, tried to in the concrete structure or structures under load before use, through the force applied, make by the tensile stress components is reduced, and even in pressure stress state of concrete component.
Preloading stress is used to reduce or offset load caused by t
6、he concrete tensile stress, and the structure of the components in the smaller tensile stress control range, and even in the compression state, to delay the generation of crack in concrete and development, so as to improve the anti-cracking performance component and rigidity.
Main text
Prestresse
7、d concrete component to the method of pretensioned stressing and posttensioned.
1.pretensioned stressing
In the concrete pouring, first by steel wire steel strand or will be composed of the prestressed tendon pulled to a specified stress, and the anchorage anchor in a pier at both ends pedestal, t
8、hen installation template, the structure, steel and parts, and then pouring concrete and maintenance. When concrete after the specified strength, relax a pier at both ends of the tendons, through the bond will be the prestressed concrete and tension to produce preloading stress. A method based on fi
9、rst relatively advantageous pedestal long, the longest useful to more than one hundred meters, so sometimes called long term method.
2. Posttensioned.
Firstly perfusion components ,then directly on prestressed method in the component. The general method is placed first after prestressed reinfor
10、cement of hole into a casing, the structure, steel and parts, then install the template and pouring concrete. Tendons first through the casing can also wear after. Concrete to strength, with a jack will introduces the pull to the stress and load demand anchor at each end of preloading stress at both
11、 ends by the anchorage to concrete component. In order to protect the tendons from corrosion and restore prestressed concrete and between the rapping, prestressed steel casing and the space between the water filling slurry must be real. Water in the mud up preservative effect, but also beneficial to
12、 restore prestressed concrete and between the rapping. In order to facilitate the construction, sometimes also can be used in the prestressed steel surface coating corrosion materials and plastic casing or oiled paper parcel of unbonded post-tensioned pre-stressing concrete muscle.
The characterist
13、ics of prestressed concrete.
(1).Improve the component of crack resistance. Because of a bear before the loading of prestressed concrete structures in the tension zone for preloading stress exists, so outside load, only when the prestressed concrete is all turned to offset the tensile and tensile
14、strain is more than concrete ultimate tensile strain, component will craze. While general reinforced concrete structure are not present in the prestressing, the cracking of the size of the load only by concrete ultimate tensile strength, compressive strength for about 1/10 of the) have decided, and
15、crack ability is very low.
(2). Increase the stiffness of the component. Because of the prestressed concrete component of normal use, in the load effect under standard combination may not cracking or only a small cracks, concrete was basically in the elastic stage work, and the stiffness of the com
16、ponent than ordinary reinforced concrete member is increased.
(3). Make full use of the high strength materials. As mentioned previously, common reinforced concrete members cant make full use of high strength materials. And prestressed concrete component, prestressed reinforced first is expected to
17、 pull, and then out load reinforced stress further increases, and should be always in high tensile stress state, that is, can effectively use high strength reinforced; And the strength of reinforced high, can reduce the need to the section area. At the same time, should as far as possible using high
18、 strength grade of concrete, and high strength steel to coordinates, to get better economic component section size.
(4). Expand the application range of the component. Because of the prestressed concrete improvement component crack resistance, and can be used for waterproof, permeability and corros
19、ion resistance requirements of the environment; Using high strength materials, the structure to be dexterous, rigidity, distortion, and can be used in the large span and heavy load and load under repeated the structure.
Prestressed concrete has been widely applied to industrial and civil building a
20、nd transportation construction. For example, 冂 prestressed concrete hollow slab shape roof board, roof, roof beam, crane beam, pre-stress Bridges, railway sleeper used in great quantities such as already. In hydraulic structure also has used to build dock, zhanqiao pier, pile, gate, DiaoDuShi, press
21、ure conduit, circular pool, aqueduct, road, bridge, and work the roofing beams and hydropower station workshop crane beam structure component, also can used for the method of prestressed reinforced dam, tunnel lining. For some have unique requirements of the structure, such as the need to prevent wa
22、ter corrosion sea platforms, resistance to high temperature and high pressure nuclear power plants, large pressure vessel etc, using prestressed concrete structure is more its superiority, instead of other structure can match.
Twenty years to build up a large number of prestressed concrete engineer
23、ing, Among them are representative of the project have 63 layer prestressed concrete floor of guangdong international building; 214 meters tall Qingdao boc building; Monomer prestressed concrete is the biggest of the capital international airport new terminal, etc. (2) the prestressed concrete bridg
24、e structure development history in 1955, the railway departments in our country the successful development of the first piece of 12 m span of prestressed concrete railway bridge, built in 1956 28 hole 24 m new YiHe across the bridge. In 1957, the highway department in Beijing to build the first seat
25、 zhoukoudian prestressed concrete road test bridge, for single span 20 meters simply-supported T bridge. Built in 1959 in lanzhou qilihe HuangHeQiao, 7 main hole for 37.5 m cantilever beam bridge. And HuangHeQiao built new town, for five hole 33 m bridge model T simply supported and hole 66 m the bo
26、wstring arch bridge.
Discussions
Concrete is brittle material, high compressive strength, tensile/flexural strength but is low. Concrete tension or the bending, in a very small tensile stress/tensile strain state will craze. Ordinary steel reinforced concrete structure, such as beam, plate, genera
27、l is being bending state, often reinforced havent under great flexural stress, concrete bending area has by cracking, and may even make reinforced exposure and rust. Therefore, the common reinforced concrete beam slab structure, the bearing capacity of the steel is far from plays out.
Prestressed c
28、oncrete is the high strength steel wire steel or along the flexural in advance by the direction for tension, and the tension is reinforced concrete in anchorage, so that by the structure of concrete flexural direction on the preloading stress. Control the size of the compressive pre-stress, can ensu
29、re that prestressed beams under bending plate design load, concrete bending area by basic do not produce tensile stress, not crack, can greatly improve the bearing capacity of beams and slabs.
Technology make full use of the prestressed concrete compressive strength and high tensile strength of rei
30、nforced high characteristics, use material "foster strengths and circumvent weaknesses", greatly broaden the compound material engineering applications. At present, able to build big span reinforced concrete bridge, floor, tall buildings such as TV tower, etc, are all dependent on prestressed concre
31、te technology.
The loss of prestress mainly comes from the creep of engineering materials, namely in long-term stress the influence of permanent deformation. Press press concrete and tension of prestressed reinforced or steel strand, also can produce creep, lead to the loss of prestress. However, i
32、n the prestressed concrete structure design and calculation prestress loss of prestress will be taken into account.
Prestressed concrete is generally used to build big span structure or decrease the structure building section, and the dimension. Choose high strength concrete and steel material will
33、 be, and can only be imposed higher the added stress, effectively increase or decrease the span structure structure section. Resistance to good, rigidity. Because of component prestress, greatly delayed the occurrence of crack, using in the load, component dont crack, or make crack delayed emergence
34、, so improved the stiffness of the component, increased the durability of structures. Save material, reducing weight. Its structure because must use high strength materials, so it can reduce the dosage of steel and the component section size, save a steel and concrete, reduce weight structure, the l
35、arge span and heavy load structure has the obvious superiority. Improve the shear capacity component. Test show that the longitudinal prestressed reinforced plays the role of anchor bolts, hindering component of inclined cracks appear and implementation, and because the curve of the prestressed conc
36、rete beams reinforced (beam) vertical component of force will be partly offset shear. Improve the stability of the members under. When the members under long fine is large, in be certain pressure then easy is bent, so that lose stability and destruction. If the reinforced concrete column prestress,
37、make the longitudinal force reinforced tension very tight, not only prestressed reinforced itself is not easy to bending, and help to improve the resistance of concrete bending around the ability.
Improve the resistance of the component fatigue performance. Because has strong of prestressed reinfor
38、ced, in use for add lotus stage or unloading the stress changes caused by relatively small, therefore, can improve the anti-fatigue strength, this to bear the structure of the dynamic loads is very favorable. But, the complicated process of high quality requirements, they need to have a technology i
39、s equipped with skilled professional team. Need to have a certain special equipment, such as drawing machines, grouting equipment, etc. Prestressed concrete structure of the construction cost is larger, the number of components of the project with high cost less.
Summary
In order to adapt to the d
40、evelopment of our national economy, ease traffic problem for people from the inconvenience of production and life, the application of prestressed concrete structure will be more wide range, so we should strengthen the improve the technical level of the prestressed scientific research work. And compa
41、red with that of the developed countries we prestressed concrete engineering of relatively backward. With our existing strong team, and some units in prestressed technique extension of earned income strength can bear and finish the important scientific research task. At the same time, the design and
42、 construction of the separation is also effect on our countrys rapid development of prestressed concrete structures are one of the factors. So it is necessary to established large powerful prestressed concrete engineering company, take on the major prestressed concrete engineering, and new technology for development research, and do well with the design and construction of the relationship between the, in order to improve the level of prestressed technique in our country.
References
李國(guó)平.預(yù)應(yīng)力混凝土結(jié)構(gòu)發(fā)展史.建筑,2008
陳嘉輝.預(yù)應(yīng)力鋼筋混凝土在建筑中的應(yīng)用研究.建筑技術(shù),2009
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Prestressed Concrete Technology預(yù)應(yīng)力混凝土英語論文
