Mechanical Writings

Carbon fiber reinforced composite materials in bridge engineering in the use
Abstract: The carbon fiber reinforced composite materials in bridge engineering advantage of and made a number of issues. Carbon fiber composites (CFRP) with light weight and strength advantages, especially in bridge engineering bridge reinforcement project has wide application value.
Key words: carbon fiber; reinforcement; Bridge
80-90 years, the rapid development of China's automobile transportation, automobile increasingly large, heavy, traffic volume increased year by year, to existing roads and bridges caused by the increasing pressure. Combined with the standard design and construction at the old bridge, and its serious shortage of capacity. According to statistics, about 5,500 of these bridges. To make these old bridges can continue to play its role in carrying, to be its reinforcement. At present, reinforced concrete bridges on the main methods for pressure grouting, injection mortar method, bridge reinforcement layer of reinforcement method, the lower beam section Enhancement Act, plate bonding method, additional longitudinal method, changing the structural system reinforcement method, prestressed reinforcement method [1].
In recent years, foreign use of carbon fiber composite (CFRP) to replace steel plates, reinforcement technology to make fundamental changes have taken place.
1 CFRP reinforcement material characteristics and advantages of the bridge
1.1 CFRP material characteristics
Carbon fiber is light weight, high strength, good corrosion resistance, easy construction and so on. Especially for high elastic modulus carbon fiber, its tensile strength than steel, 68 times the big, big steel elastic modulus ratio 1.8-2.6 times; at 600 ℃ high temperature performance remains unchanged, still at -180 ℃ low temperature flexibility ; acid, alkali and salt corrosion environment does not occur. Specific mechanical properties in Table 1. For this reason, in recent years in foreign countries to use more. In reinforcing the start is usually adopted in CFRP plate, and later evolved to the use of CFRP cloth. This is because the CFRP fabric is more flexible and convenient to use, and transport is also very convenient. Shown in Figure 1, the excellent performance of the CFRP tensile fabric with epoxy paste to the surface or the box beam wall, to join with the original structure of the force, the CFRP fabric and the original layout of reinforced concrete structures to bear tension, improve the structure of the bearing capacity.
1.2 CFRP Sheet Strengthening the advantages of a bridge
1) does not increase the dead load and the section size;
2) The material is thin, so it will not reduce the clearance under the bridge;
3) The construction is convenient, especially when working space inside the box is limited, its good maneuverability, and can not affect or less impact on traffic in the case of reinforcement construction, while construction method to overcome the reinforcing steel bonding Paste the length of steel plate by transport limitations caused by steel corrosion between steel and concrete beam damage such as lack of bonding layer;
4) The different components can be adapted to the shape, forming a very convenient;
5) by epoxy resin bonding materials and structures effectively, not need to set anchor bolts, and no new damage to the original structure;
6), according to the force need to paste a number of layers;
7) as a composite material with excellent chemical resistance;
8) reinforcement costs low. Meier, Kaiser, Saadatmamesh, Ehsani, Triantafillou, Ritchie et al CFRP cloth pasted against the concrete beams strengthened with theoretical and experimental studies have shown that using cloth instead of CFRP plate reinforced concrete beams can save about 25% of funds.
2 CFRP Sheet Strengthening the damage type of concrete structure
CFRP Sheet Strengthening the overall effect of concrete structures, mainly through its bond with concrete to achieve between the good, any damage caused by factors that are bonded area may lead to the destruction of the structure can not sudden strengthening of the desired effect. Even if the bond did not lead to the ultimate destruction of the interface also the bonding interface cracks and expansion of the reinforcement strength, stiffness and deformation capacity of a direct impact. CFRP Sheet Strengthening, the study found the force of its destruction has the following characteristics [1]:
First of all, when the CFRP reinforcement is too large, for example, paste the five CFRP cloth beam, and a reliable anchor, it will cause Class of muscle damage. That is reinforced by the pull-off yield and carbon Wei Bula, before being crushed concrete compression zone, with the obvious nature of brittle fracture. When such damage occurs, CFRP stress reaches its ultimate strength is only about 1 / 10, far from its strength into full play, and the destruction of the brittle nature of the time significantly. By calculating the amount of CFRP cloth, which limit the amount of CFRP reinforcement to control.
Another feature is the destruction of protective layer of concrete tensile shear debonding failure occurred. The role of the structural adhesive produced in the concrete surface and shear stress, and the role of normal stress caused by a combination of horizontal fracture, with cracks and expansion levels, resulting in concrete cover is Paxia. As between the CFRP fabric and structure of adhesive, structural adhesive bond strength between concrete, in the case of quality assurance, are greater than the concrete (or the surface of shallow concrete) the tensile strength, so the vast majority of stripping damage occurred in the protective layer of concrete structures within the region, as well as through structural measures to control the amount of CFRP cloth type of cracks. For example, layering additional anchor to increase the anchorage length, and strictly control the construction quality, strict component surface treatment. In addition, the literature [2] shows, CFRP and the concrete base cloth material strength of the bond between the lower anchorage length less than, or less unevenly applied adhesive, concrete cracks appeared in a wide bend or shear cracks, uneven concrete surface, fatigue loads, etc., can also cause cloth material and debonding between the concrete surface.
These two have a significant debonding brittle, in the application should be avoided.
3 CFRP sheets and calculation of solid design principles
3.1 CFRP Sheet Strengthening the basic guiding idea of the design
1) For the appearance of good, low steel corrosion, cracking of concrete cover member yet, that is slightly corroded reinforced concrete structures, in the calculation of bearing capacity, can be considered self-reinforcement and concrete strength and bond strength between them are not reduced. Therefore, such carbon fiber reinforced components, only the reinforcement of preventive anti-corrosion can to improve the components in the corrosion resistance under unfavorable conditions. Such reinforcement either structural reinforcement, do not have to calculate the required number of CFRP cloth.
2) The cracking of concrete cover has been severely corroded reinforced concrete structure, reinforced steel cross-sectional area makes the reduction of corrosion, resulting in reduced carrying capacity of steel, and the cohesive force between the reinforcement and concrete strength due to reduced losses. Making carbon fiber reinforcement, the structure should be the extent of corrosion for different computing the required number of vertical CFRP cloth to enhance the flexural capacity; calculate the number of transverse CFRP cloth to enhance the shear capacity. It should be noted that: structural reinforcement is the strength of the components to restore and improve, rather than make up for the loss of steel.
3.2 The amount of carbon fiber
The literature [3] Crack width and the relationship between bearing capacity reduces to:
Where: Md-rust bearing capacity (kN.m); M0-normal component capacity (kN.m); W-crack width (mm).
Thus, according to section forms, lack of bending resistance can be estimated by cross-sectional area of reinforcement required for As, CFRP cloth dosage can be calculated as follows [3]:
Where: Ac-CFRP cloth cross-sectional area (mm2); As a reinforcement to resist cross-sectional area less than the required moment (mm2); σу-steel yield strength (mm2); σd-CFRP fabric of the allowable tensile stress (usually take the tensile strength of 2 / 3, to 1.67 × 103MPa).
Anchorage length of 3.3
Between CFRP and concrete bonded fabric performance, in terms of stress and strain distribution or distribution, there is some effective anchorage length.
Under different load levels from the strain distribution curve (Figure 2) can be seen that strain curve at different load levels, in addition to a difference of magnitude outside the shape of the curve is very similar to that in the CFRP strain and stress distribution in the smooth development; Meanwhile, bond strain and stress cracks in the main away from the obvious changes within 50mm. That, CFRP cloth around Bond length is appropriate to take 100mm.
Figure 2 Distribution of different load levels, strain curve
4 Application
Japan Highway Public Corporation research institute in the CFRP reinforcement were tested in rectangular beams based on Tokyo on the Tomei Expressway Viaduct was reinforced. Two-span continuous concrete bridge box girder bridge, painted the scene with CFRP cloth resin inside and outside the paste container bridge reinforcement. Test shows that the actual reinforcement effect in good agreement with the theoretical results, the carbon fiber strength to play a more full. Japan has also used carbon fiber for reinforced concrete piers, the pier outside the wound fibers, the strength of the pier and the stress state has been markedly improved.
5 CFRP Sheet Strengthening the prospects and problems of application
CFRP came out half a century, the traditional materials because of its less than the physical, mechanical and chemical properties, and its price has been gradually approaching the price of traditional materials in many areas has been widely used. Although CFRP material deficiencies in some respects, but with the testing and further improve the manufacturing process, these issues are expected to be resolved. Can be predicted that in the future bridge construction, CFRP materials will be further applications.
CFRP plates with paste or reinforced CFRP Sheet Strengthening the existing structure of the paste was reinforced beam construction technology and long-term performance, including the fiber or fabric CFRP cured adhesives aging performance, durability, creep and shrinkage of the adhesive properties of beam impact and the reliability of beam and fatigue reliability, have yet to be studied further.

"Light Industry Machinery" 2009 03 Collection for the latest apply to double-tube hydraulic bulge of the equivalent yield strength method Guo associated Liufu Jun Jin-Yang Zheng Guo-Hui Zhu Xu Ming Ze Abstract: Expansion hydraulic pressure the size of the double-tube hydraulic bulge process play a decisive role, so to accurately determine the range of hydraulic pressure bulge is essential. The paper analyzed on the basis of previous work, proposed for double-tube hydraulic bulge equivalent yield strength of law, given to determine the equivalent yield strength of the concrete steps. The results show that: using this method can improve the accuracy of theoretical calculations, in good agreement with the experimental data, calculated data and experimental values of relative error between 0.96% to 1.02%, and the double-tube hydraulic bulge industry production of a more scientific basis. 【Author】: Institute of Chemical Machinery, Zhejiang University; Zhejiang Special Equipment Inspection Institute; ARC Pressure Vessel Co., Ltd.;
Key words: double-tube hydraulic bulge equivalent yield strength of hydraulic pressure bulge theory elastic-perfectly plastic material true stress-strain curves calculated Hydraulic Expansion Tube
【Fund】: Zhejiang Province in a major scientific and technological projects funded (2006c13002)
【Keywords】: TG394
】 【DOI: CNKI: SUN: QGJX.0.2009-03-008
Snapshot】 【Text: 1 double tube of the problem, or coated pipe, the inner tube and outer tubes, both inside and outside the tube the same or not the same material, pipe layer closely by external force role, both within and outside the tube deformation, shown in Figure 1. Double-tube studies abroad began in the 20th century, 80 years, the corrosion was mainly used in more serious situations. Coated with carbon steel such as stainless steel instead of pure stainless steel used in submarine similar documents to download full text of more full text PDF format CAJ text format
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