Reinforced Concrete (RC) (also called reinforced concrete or RCC) is a composite material in which the relatively low strength of the pull and ductility of the concrete is offset by the inclusion of higher reinforcement. tensile strength or tenacity. The reinforcement is usually, though not necessarily, reinforcing steel (rebar) and is usually embedded passively in the concrete before the concrete set. The reinforcement scheme is generally designed to withstand tensile stresses in certain areas of the concrete that may cause unacceptable cracking and/or structural failure. Modern reinforced concrete may contain a variety of reinforcing materials made of steel, polymer or alternative composite materials in conjunction with rebar or not. Reinforced concrete can also be permanently stressed (concrete in compression, strengthening in tension), so as to improve the behavior of the final structure under the workload. In the United States, the most common method of doing this is known as pre-tension and post-tension.
For robust, durable and durable construction, the reinforcement shall have the following properties at least:
- High relative strength
- High tensile tolerance
- A good bond on concrete, regardless of pH, moisture, and similar factors
- Thermal compatibility, does not cause unacceptable pressure in response to temperature changes.
- Resilience in concrete environments, regardless of sustained corrosion or stress eg.
Video Reinforced concrete
History
FranÃÆ'§ois Coignet was a French industrialist in the nineteenth century, a pioneer in the development of structural, prefabricated and boned concrete. Coignets were the first to use reinforced concrete as a technique for building structures. In 1853, Coignet built the first steel-reinforced concrete structure, a four-storey house in 72 rue Charles Michels on the outskirts of Paris. Coignet's description of reinforced concrete suggests that he did not do so to add strength to the concrete but to keep the walls in monolithic construction from upside down. In 1854, the English builder William B. Wilkinson reinforced the concrete roof and floor in his two-story house. His position of reinforcement shows that, unlike his predecessor, he has knowledge of tensile stress.
Joseph Monier, a French gardener and known as one of the main discoverers of reinforced concrete, was granted a patent for a flower pot reinforced by mixing wire mesh into mortar shells. In 1877, Monier was granted another patent for a more advanced technique of reinforcing concrete columns and beam gears with iron bars placed in a grid pattern. Although Monier no doubt knows that reinforced concrete will improve his inner cohesion, it's less known if he even knows how much reinforcement actually increases the tensile strength of the concrete.
Prior to 1877 the use of concrete construction, though originating from the Roman Empire, and having been reintroduced in the early 1800s, has not been a proven scientific technology. American New Yorker Thaddeus Hyatt publishes a report titled Multiple Experimental Accounts with Portland-Cemented Concrete Combined with Iron as Building Materials, with Reference to Metal Economics in Construction and for Fire Security in Roof, Floor, and Surface Working where he reported his experiment on reinforced concrete behavior. His work plays a major role in the evolution of concrete construction as a science that is proven and studied. Without Hyatt's work, more dangerous trial and error methods will rely heavily on technological advances.
G. A. Wayss is a German civil engineer and pioneer of iron and steel concrete construction. In 1879, Wayss purchased the German rights to the Monier patent and in 1884, he began the first commercial use of reinforced concrete in his company Wayss & amp; Freytag. Until the 1890s, Wayss and his company contributed greatly to the progress of Monier's reinforcement system and established it as a well-developed scientific technology.
Ernest L. Ransome is a British-born engineer and early inventor of reinforced concrete techniques at the end of the 19th century. With the knowledge of reinforced concrete developed over the previous 50 years, Ransome innovates almost all the styles and techniques of the inventors of previously known reinforced concrete. The key innovation of Ransome is rotating the reinforcing steel rods that increase the bonding with the concrete. Gaining increased fame from its concrete buildings, Ransome was able to build two of the first reinforced concrete bridges in North America. One of the first concrete buildings built in the United States, is a private home, designed by William Ward in 1871. The house was designed to be fire-resistant for his wife.
One of the first skyscrapers made with reinforced concrete is a 16-storey Ingalls Building in Cincinnati, built in 1904.
The first reinforced concrete building in Southern California was Laughlin Annex in Downtown Los Angeles, built in 1905. In 1906, 16 building permits were reportedly issued for reinforced concrete buildings in the City of Los Angeles, including the Temple Auditorium and the 8th floor Hayward Hotel.
On April 18, 1906 a magnitude 7.8 earthquake struck San Francisco. The strong ground shook and the next fire destroyed most of the city and killed thousands of people. The use of reinforced concrete after the quake is heavily promoted in the US construction industry because of its non-flammability and is considered to have superior seismic performance compared to masonry.
In 1906, partly the collapse of the Bixby Hotel in Long Beach killed 10 workers during construction when shoring was removed prematurely. This event spurred observations of concrete erection practices and building inspections. This structure is constructed from reinforced concrete framework with hollow hollow clay tile floors and hollow clay tile fill walls. This practice is highly questionable by experts and recommendations for "pure" concrete construction using reinforced concrete for floor and walls as well as frames made.
The National Cement User Association (NACU) was published in 1906 "Standard No. 1", and in 1910 "Standard Building Regulations for Reinforced Concrete Use".
Maps Reinforced concrete
Use in construction
Many types of structures and different structural components can be constructed using reinforced concrete including slabs, walls, beams, columns, foundations, skeletons and more.
Reinforced concrete can be classified as precast or cast-in-place concrete.
Designing and implementing the most efficient flooring system is the key to creating the optimal structure of the building. Small changes in floor system design can have a significant impact on material costs, construction schedules, final strength, operating costs, occupancy rates and end use of buildings.
Without reinforcement, building a modern structure with concrete material would not be possible.
Behavior of reinforced concrete
Materials
Concrete is a coarse mixture (gravel or brick) and fine aggregate (usually sandstone or crushed stone) with a paste of a binder (usually Portland cement) and water. When the cement is mixed with a little water, it is hydrated to form a microscopic opaque crystal lattice that encloses and locks the aggregate into a rigid structure. Aggregates used to make concrete must be free of harmful substances such as organic waste, dust, clay, lignite, etc. The typical concrete mixture has a high resistance to compressive stress (about 4,000 psi (28 MPa)); however, a large voltage ( for example, due to bending) will break the microscopic rigid lattice, resulting in cracking and concrete separation. For this reason, the typical non-reinforcing concrete must be well supported to prevent the development of tension.
If the material with high strength in voltage, such as steel, is placed in concrete, then the composite material, reinforced concrete, not only withstand compression but also bending and other direct pull action. A composite section in which concrete rejects compression and reinforcement "rebar" resisting tension can be made into almost any shape and size for the construction industry.
Primary characteristics
Three physical characteristics give the concrete a special property:
- The coefficient of thermal expansion of concrete is similar to steel, eliminating the large internal pressure due to differences in thermal expansion or contraction.
- When the cement paste inside the concrete hardens, this corresponds to the steel surface detail, allowing each pressure to be efficiently transmitted between different materials. Usually rough or wavy steel bars to further enhance the bonding or cohesion between concrete and steel.
- The alkaline chemical environment provided by the alkaline reserves (KOH, NaOH) and portlandite (calcium hydroxide) contained in the hardened cement paste causes the passive film to form on the steel surface, making it more resistant to corrosion. than in neutral or acid conditions. When the cement paste is exposed to air and meteoric water reacts with atmospheric CO 2 , the portlandite and calcium silicate hydrate (CSH) of the hardened cement paste become increasingly carbonated and the high pH gradually decreases from 13.5 to 12 , 5 to 8.5, the pH of water in equilibrium with calcite (calcium carbonate) and steel is no longer passivated.
As a rule of thumb, just to give an idea of ​​the order of magnitude, the steel is protected at a pH above ~ 11 but begins to corrode below ~ 10 depending on the characteristics of steel and local physical-chemical conditions when the concrete becomes carbonated. Carbonation of concrete along with the inclusion of chloride is one of the main reasons for the failure of the reinforcement bar in concrete.
The relative cross-sectional area of ​​steel required for ordinary reinforced concrete is usually quite small and varies from 1% for most beams and slabs to 6% for some columns. Bolt bolts are usually round and vary in diameter. Structures of reinforced concrete sometimes have provisions such as a ventilated ventilated core to control moisture & amp; humidity.
The distribution of strength characteristics of concrete (apart from reinforcement) as long as the cross section of the vertical reinforced concrete element is not homogeneous.
Composite and concrete composite action mechanisms
Strengthening in RC structures, such as steel rods, must undergo the same strain or deformation as the surrounding concrete to prevent discontinuity, slip or separation of the two materials under load. Maintaining composite action requires the transfer of loads between concrete and steel. Direct stress is transferred from the concrete to the interface bar so as to change the tensile stress on the reinforcement rod along its length, this load transfer is achieved by using anchorage and is idealized as a continuous stress field that develops around the concrete-steel interface.
Anchorage in the concrete: Specification code
Since the actual bond stress varies along the length of the bars anchored in the tension zone, the current international specification code uses a long development concept rather than bonding stress. The main requirement for the safety of bond failure is to provide sufficient extension of the length of the bar outside the point where steel is required to develop this yield stress and length should be at least equal to its development length. However, if the actual available length is not sufficient for full development, special couriers must be provided, such as wheels or hooks or mechanical end plates. The same concept applies to the length of the splice connection mentioned in the code where the splices (overlap) are provided between two adjacent bars to maintain the required voltage continuity in the splice zone.
Size of anti-corrosion
In wet and cold climates, reinforced concrete for roads, bridges, parking structures and other structures that may be exposed to deicing salts may benefit from the use of corrosion resistant reinforcement such as uncoated, low carbon/chromium (microcomposites), epoxy coated, hot dip galvanized or stainless steel rebar. Good design and well chosen concrete mix will provide additional protection for many applications. Rebar carbon/chrome that is not coated and looks like standard carbon steel due to lack of coating; highly corrosion-resistant features inherent in the steel micro structure. This can be identified by specified ASTM designations at the conclusion of fine and dark charcoal. Epoxy coated rebar can be easily identified by the light green color of the epoxy coating. Hot dip galvanized rebar may be light or dull gray depending on the length of exposure, and stainless rebar shows a typical white metal sheen that is easily distinguished from carbon steel reinforcing steel. Reference specification standard ASTM A1035/A1035M Standard Specification for Formulated and Low Carbon Concrete Carbon, Chromium, Steel for Reinforcement Concrete, A767 Standard Specification for Hot Dip Galvanized Reinforcing Bars < b> A775 Standard Specification for Reinforcing Steel Epoxy Coated Bar and A955 Standard Specification for Iron Concrete and Ordinary Concrete Iron Concrete for Reinforcement Concrete.
Another cheaper way to protect reinforcement is to coat them with zinc phosphate. Zinc phosphate slowly reacts with calcium cations and hydroxyl anions present in cement pore water and form a stable hydroxyapatite coating.
Penetrating sealants should normally be applied some time after the preservation process. Sealants include paints, plastic foams, films and aluminum foil, forged or mats sealed with tar, and a layer of bentonite clay, sometimes used to seal the road.
Corrosion inhibitors, such as calcium nitrite [Ca (NOT 2 ) 2 ], can also be added to the water mixture before pouring the concrete. Generally, 1-2% by weight of Ca (NO 2 ) 2 ] with respect to the weight of the cement is required to prevent corrosion of the reinforcement. Anion nitrite is a light oxidizer that oxidizes dissolved iron (Fe2up/2>/oz) ions present on a rusted steel surface and causes it to precipitate as an insoluble iron hydroxide (Fe (OH) 3 ). This causes steel passivation at the anodic oxidation site. Nitrite is a much more active inhibitor of corrosion than nitrate, which is a less powerful oxidizer of divalent iron.
Strengthening and block terminology
The beam curved under the bending moment, resulting in a small curvature. In the outer face (the face of tensile) of the curvature, the concrete experiences tensile stress, while the inner face (press face) undergoes compressive pressure.
The single reinforced beam is one in which the concrete element is only reinforced near the tensile face and the amplifier, called the taut steel, is designed to withstand tension.
Double reinforced rays are one in which addition of reinforcement of reinforced concrete elements is also strengthened near the compressed surface to aid the compression of holding the concrete. Last reinforcement is called compression steel. When the concrete compression zone is inadequate to withstand the tap moments (positive moments), extra strengthening should be given if the architect limits the dimensions of the part.
The below-strengthened ray is one where the tensile capacity of the tensile ampli fi er is less than the combined compression capacity of the concrete and the compression steel (under-reinforced on the tensile surface). When the reinforced concrete element experiences an increase in bending moment, the reinforcing steel will produce the concrete not reaching its main failure condition. As strained steel produces and stretches, the "less reinforced concrete" also produces in a resilient manner, indicating massive deformation and warning before its main failure. In this case the melting steel stress regulates the design.
The over-reinforced ray is one in which the stress capacity of the reinforcing steel is greater than the combined compression capacity of the concrete and the compression steel (too reinforced on the tensile surface). Thus, the "over-reinforced concrete" beams fail by crushing the push zone concrete and prior to the voltage zone steel results, which do not provide a warning prior to failure because the failure occurs instantly.
The balanced-reinforced ray is one in which both push and pull zones achieve results at the same load applied to the beam, and the concrete will be destroyed and the tensile steel will produce at the same time. This design criterion is as risky as excessive reinforced concrete, due to abrupt failure because the concrete crushes at the same time as the tensile steel yield, which gives little warning of pressure on the voltage failure.
The reinforced concrete moment steel element shall normally be designed so as not to be reinforced so that the user of the structure will receive an impending warning of collapse.
Characteristic strength is the material strength in which less than 5% of specimens exhibit lower strength.
The design strength or nominal strength is the material strength, including the material safety factor. The value of the safety factor generally ranges from 0.75 to 0.85 in the design of allowable voltage.
the boundary condition is the theoretical failure point with a certain probability. This is stated under the load factor and the resistance being taken into account.
Structures of reinforced concrete are usually designed in accordance with rules and regulations or code recommendations such as ACI-318, CEB, Eurocode 2 or the like. WSD, USD or LRFD methods are used in the design of RC structural members. Analysis and design of RC members can be done using a linear or non-linear approach. When applying the security factor, constructing the code usually proposes a linear approximation, but for some cases the approach is nonlinear. To see examples of non-linear numerical simulations and calculations, visit the reference:
Prestressed concrete
Prestressed concrete is a technique that greatly increases the load strength of concrete beams. The reinforcing steel at the bottom of the beam, which will be subjected to tension when in service, is placed in tension before the concrete is poured around it. After the concrete hardens, the tension on the reinforcing steel is released, placing a compressive force mounted on the concrete. When the load is applied, the reinforcing steel takes more pressure and the compressive force in the concrete decreases, but does not become tensile. Since the concrete is always under pressure, it is less subject to cracks and failures.
Common failure mode of steel reinforced concrete
Reinforced concrete can fail because of inadequate strength, which causes mechanical failure, or due to decreased endurance. Corrosion and freezing/liquefaction cycles can damage poorly designed or poorly constructed concrete. When the rebar is corroded, the oxidation product (rust) expands and tends to peel, crack the concrete and not bind the rebar of the concrete. Typical mechanisms that lead to resilience issues are discussed below.
Mechanical failure
The cracking of the concrete is almost impossible to prevent; however, the size and location of the cracks may be limited and controlled by appropriate reinforcement, control connections, preservation methodologies and mixed concrete designs. Cracks can allow moisture to penetrate and corrode the reinforcement. This is a failure of serviceability in the design of state boundaries. Cracks are usually the result of an inadequate amount of rebar, or rebar that is too far apart. The concrete then cracks either under excessive loading, or due to internal effects such as initial thermal shrinkage when healing.
The main failure leading to collapse can be caused by the destruction of the concrete, which occurs when the compressive stress exceeds its power, by producing or failure of the rebar when bending or shear stress exceeds the strength of the reinforcement, or by the failure of the bond between the concrete and the concrete. rebar.
Carbonation
Carbonation, or neutralization, is a chemical reaction between carbon dioxide in the air and calcium hydroxide and hydrated calcium silicate in concrete.
When a concrete structure is designed, it is usually to determine the concrete cover for rebar (the depth of rebar in the object). The minimum concrete cover is usually governed by a design or building code. If the reinforcement is too close to the surface, initial failure due to corrosion can occur. The depth of the concrete cover can be measured with a meter cover. However, carbonated concrete raises the problem of endurance only when there is also enough moisture and oxygen to cause electrophotental corrosion of the reinforcing steel.
One method of testing the carbonate structure is to drill a new hole on the surface and then treat the cut surface with a phenolphthalein indicator solution. This solution turns pink when in contact with alkaline concrete, making it possible to see the depth of carbonation. Using an existing hole is not enough because the open surface will already be carbonated.
Chlorides
Chlorides, including sodium chloride, can increase the corrosion of the embedded steel rebar if present in sufficiently high concentrations. Anion chloride induces local corrosion (corrosion of the wells) and general corrosion of reinforcing steel. For this reason, one should only use fresh raw water or drinking water to mix the concrete, ensuring that the coarse and fine aggregates contain no chloride, rather than mixing which may contain chloride.
It was formerly common for calcium chloride to be used as a mixture to promote fast concrete arrangements. It also mistakenly believes that it will prevent freezing. However, this practice becomes undesirable once the damaging effects of chloride are known. This should be avoided as much as possible.
The use of de-icing salt on the highway, used to lower the freezing point of water, may be one of the main causes of premature failure from reinforced or prestressed concrete bridges, highways, and parking garages. The use of multi-layered reinforcement reinforcement and the application of cathodic protection has reduced this problem to some extent. Also, FRP (fiber-reinforced polymer) reinforcement is known to be less susceptible to chloride. Properly designed concrete mixtures that have been properly permitted to be healed are effectively resistant to the effects of frozen ice.
Another important source of chloride ions is sea water. Sea water contains about 3.5% by weight of salt. These salts include sodium chloride, magnesium sulphate, calcium sulphate, and bicarbonate. In water, these salts dissociate in free ions (Na , Mg 2 , Cl - , SO 4 2 - , HCO 3 - ) and migrate with water to the capillaries of the concrete. Chloride ions, which make up about 50% of these ions, are very aggressive as causes of corrosion of carbon steel reinforcement.
In the 1960s and 1970s it was also relatively common for magnesite, chloride-rich carbonate minerals, for use as floor-topping materials. This is done primarily as a layer of leveling and depletion of sound. However it is now known that when these materials come in contact with moisture, they produce a weak hydrochloric acid solution due to the presence of chloride in magnesite. Over a period of time (usually decades), solutions cause corrosion on embedded steel bars. These are most commonly found in wet areas or areas that are repeatedly exposed to moisture.
Alkali silica reaction
This amorphous silica reaction (kalsedon, chert, limestone silicate) is sometimes present in the aggregate with hydroxyl ions (OH - ) of the cement pore solution. The crystallized silica is poor (SiO 2 ) dissolves and dissociates at high pH (12.5 - 13.5) in alkaline water. Soluble soluble silicic acid reacts in porrox with calcium hydroxide (portlandite) present in the cement paste to form an expansive calcium hydrate hydrate (CSH). The alkali-silica reaction (ASR) causes local swelling which is responsible for tensile stress and cracking. The conditions required for the alkali-silica reaction are threefold: (1) aggregates containing alkali reactive constituents (amorphous silica), (2) the availability of sufficient hydroxyl ions (OH - ), and (3) enough moisture, above 75% relative humidity (RH) inside the concrete. This phenomenon is sometimes popularly referred to as "concrete cancer". This reaction occurs independently of the reinforcement; giant concrete structures such as dams can be affected.
High alumina cement conversion
Resistant to weak acids and especially sulfates, these cements recover quickly and have very high endurance and strength. It is often used after World War II to create precast concrete objects. However, it can lose power by heat or time (conversion), especially when it is not healed properly. After the collapse of three roofs made of prestressed concrete beams using high alumina cement, the cement was banned in Britain in 1976. Further questions on this issue indicate that the beam was not manufactured correctly, but the restrictions remain.
Sulphate
Sulfate (SO 4 ) in soil or in ground water, in sufficient concentration, can react with Portland cement in concrete leading to the formation of expansive products, eg, ettringite or thaumasite, which can cause early failure. of the structure. The most typical attack of this type is on concrete slabs and foundation walls in the classroom where sulfate ions, via alternate wetting and drying, can increase concentration. As concentration increases, attacks on Portland cement can begin. For structures that are buried like pipes, this type of attack is much less frequent, especially in the eastern United States. The concentration of sulfate ions increases more slowly in the soil mass and depends mainly on the initial amount of sulfate in the original soil. The chemical analysis of soil wastage to check for the presence of sulfate should be carried out during the design phase of any project involving the concrete in contact with the original soil. If concentrations are found to be aggressive, various protective layers may be applied. Also, in ASTM C150 Type 5 Portland cement can be used in mix. This type of cement is designed to withstand sulfuric attacks.
Steel plate construction
In steel plate construction, stringer joins a parallel steel plate. The platen assemblies are constructed from the site, and welded together in place to form a steel wall connected by a stringer. The walls become the shape in which the concrete is poured. The speed of construction of reinforced concrete steel construction plates by cutting manual steps that take time in place to tie rebar and building forms. This method produces excellent strength because the steel is outside, where the tensile force is often the greatest.
Reinforced concrete fiber
Fiber reinforcement is mainly used in shotcrete, but can also be used in normal concrete. Normal fiber-reinforced concrete is mostly used for floors and sidewalks on the ground, but can also be considered for various parts of construction (beams, pillars, foundations, etc.), either alone or with hand-tied reinforcement.
Concrete reinforced with fiber (which is usually steel, glass, or plastic fibers) is cheaper than the rebar of the hands tied. The shape, dimensions, and length of the fiber are very important. Short and thin fibers, such as short, hair-shaped glass fibers, are only effective during the first hour after pouring the concrete (the function is to reduce cracks while concrete is stiff), but will not increase the tensile strength of the concrete. Normally sized fibers for European shotcrete (diameter 1 mm, length 45 mm - steel or plastic) will increase the tensile strength of concrete. Fiber reinforcement is most often used to complement or replace some of the main rebar, and in some cases can be designed to completely replace rebar.
Steel is the most commonly available fiber, and has different lengths (30 to 80 mm in Europe) and shape (tip hook). Steel fibers can only be used on surfaces that can tolerate or avoid corrosion and rust stains. In some cases, the fiber-steel surface is confronted with other materials.
Glass fiber is cheap and anti-rust, but not as elastic as steel. Recently, spinning basalt fibers, long available in Eastern Europe, are available in the US and Western Europe. Basal fiber is stronger and cheaper than glass, but historically it has not withstanding the alkaline environment of Portland cement well enough to be used as a direct amplifier. The new material uses a plastic binder to isolate the basal fibers from the cement.
Premium fiber is a reinforced graphite plastic fiber, which is almost as strong as steel, lighter, and corrosion resistant. Some experiments have promising early results with carbon nanotubes, but the material is still too expensive for any building.
Non-steel strengthening
There is a lot of overlap between the non-steel reinforcing subjects and the reinforcement of concrete fibers. The introduction of non-steel reinforcing concrete is relatively new; two major forms are required: non-metallic rebar rods, and non-steel (usually non-metallic) fibers incorporated into the cement matrix. For example, there is an increasing interest in reinforced concrete glass fibers (GFRC) and in various applications of polymer fibers incorporated into the concrete. While there is currently not much suggestion that these materials will replace rebar metal, some of them have great advantages in certain applications, and there are also new applications where metal rebar is not an option. However, the design and application of non-steel booster is full of challenges. For one thing, concrete is a very alkaline environment, where many materials, including most types of glass, have a poor service life. Also, the behavior of the reinforcing material differs from the metallic behavior, for example in terms of shear strength, creep and elasticity.
Fiber-reinforced plastics/polymers (FRPs) and glass-reinforced plastics (GRPs) comprise polymer fibers, glass, carbon, aramid or other polymers or high strength fibers arranged in a resin matrix to form rebar, or lattice, or fiber rods. These reinforcements are installed in much the same way as reinforcing steel. The cost is higher but, as applicable, the structure has advantages, especially the dramatic reduction in corrosion-related problems, either by intrinsic concrete alkalinity or by external corrosive liquids that may penetrate the concrete. This structure can be much lighter and usually has a longer lifetime. The cost of these materials has dropped dramatically since their widespread adoption in the aerospace industry and by the military.
In particular, FRP rods are useful for structures in which the presence of steel will not be accepted. For example, an MRI machine has a very large magnet, and therefore requires a non-magnetic building. Again, toll stations that read radio tags require transparent reinforced concrete for radio waves. Also, where the design life of concrete structures is more important than the initial cost, non-steel reinforcement often has the advantage that corrosion of reinforcing steel is the main cause of failure. In such situations, the anti-rust builder may extend the life of the structure substantially, for example in the intertidal zone. FRP bars can also be useful in situations where it is possible that concrete structures can be compromised in the coming years, for example the edge of the balcony when the ledge is replaced, and the bathroom floor is in a multi-story construction where the service life of the floor structure is likely to be many times life waterproofing building membrane service.
Plastic strength is often stronger, or at least has a better strength and weight ratio than a reinforcing steel. Also, because it is corrosion resistant, it does not require protective concrete cover as thick as a steel booster (usually 30 to 50 mm or more). FRP reinforced structures can become lighter and last longer. Thus, for some applications, the cost of a lifetime would be a competitive price with steel reinforced concrete.
The nature of FRP or GRP bar material differs markedly from steel, so there are differences in design considerations. The FRP or GRP blades have relatively higher tensile strength but lower stiffness, so the deflections tend to be higher than for equivalent armored units. Structures with internal FRP amplifiers typically have elastic deformability comparable to the plastic deformability (ductility) of reinforced steel structures. Failure in both cases is more likely to occur by concrete compression than by breakage of reinforcement. Deflection is always a major design consideration for reinforced concrete. The deflection limit is set to ensure that the crack width in steel reinforced concrete is controlled to prevent water, air or other aggressive substances reaching the steel and causing corrosion. For FRP reinforced concrete, aesthetic and possibly impermeable water would be the limiting criterion for crack width control. FRP bars also have relatively lower compressive strength than rebar steels, and therefore require different design approaches for reinforced concrete columns.
One disadvantage for the use of FRP boosters is their limited fire resistance. Where fire safety becomes a consideration, structures using FRP must retain their strength and retain force at the expected temperature in the event of a fire. For fireproofing purposes, adequate thickness of the concrete cover or protective cladding is required. The addition of 1 kg/m 3 of polypropylene fiber to concrete has been shown to reduce spalling during fire simulation. (This increase is thought to be caused by the formation of the exit path of most of the concrete, allowing the vapor pressure to dissipate.)
Darby, A., The Airside Road Tunnel, Bandara Heathrow, Inggris,
Another problem is the effectiveness of shear reinforcement. FRP of the stirrup rebar formed by bending before hardening generally performs relatively poorly compared to steel stirrups or to structures with straight fibers. When tense, the zone between the straight area and the curve is subject to strong bending, shearing, and longitudinal pressures. Special design techniques are needed to solve the problem.
There is a growing interest in applying external reinforcement to existing structures using sophisticated materials such as rebar composites (fiberglass, basalt, carbon), which can provide tremendous power. Around the world, there are a number of composite rebar brands that are recognized by various countries, such as Aslan, DACOT, V-rod, and ComBar. The number of projects using composite rebar is increasing day by day worldwide, in countries ranging from the United States, Russia, and South Korea to Germany.
See also
References
Further reading
- Threlfall A., et al. Reinforced Concrete Designer's Reynolds Handbook - 11th edition ISBNÃ, 978-0-419-25830-8.
- Newby F., Early Reinforced Concrete , Ashgate Variorum, 2001, ISBN 978-0-86078-760-0.
- Kim, S., Surek, J and J. Baker-Jarvis. "Electromagnetic Metrology on Concrete and Corrosion." Research Journal of the National Institute of Standards and Technology , Vol. 116, No. 3 (May-June 2011): 655-669.
- Daniel R., Formwork UK "Structure of the concrete frame." .
External links
- The Steel Reinforcement Institute (CRSI) is a national trade association that stands as an authoritative resource for information related to steel reinforced concrete construction.
- Concrete Research: http://www.concreteresearch.org
- Timeline from concrete
Source of the article : Wikipedia
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