High Performance Fiber Reinforced Concrete In Earthquake-resistant Construction

The advantages of using work-hardening, high-performance fiber reinforced concrete (HPFRC) in critical areas of earthquake resistant structures are increasingly recognized. Due to their ductile behavior HPFRCs is particularly attractive for use in areas where a large inelastic deformation capacity is needed to withstand the demands caused by a severe earthquake. Test results showed that HPFRCs serve as a substitute for specific details of seismic reinforcement by providing additional shear strength and confinement, which could lead to important simplifications in the construction of earthquake resistant structures.

In 1987, Naaman proposes to classify the fiber reinforced concrete is based on the tensile behavior after cracking (Fig. 1). When the rate of hardening behavior has been observed, the mixture is classified as high-performance fiber reinforced cement (HPFRC). When the strain softening behavior is observed, the mixture is classified as a simple fiber reinforced concrete (FRC).

After the first crack occurs HPFRC subjected to direct tension, the fibers bridge the crack to carry a greater load, thus increasing the composite cracking. This cracking process, which eventually leads to a dense mass of fine cracks, damage continues to locate the (substantial removal of the fiber) is one or a few cracks, traction typically between 0.5 and 3%. FRC on a regular basis, on the other hand, because the fibers can not carry more load after cracking, the location of damage will start as soon as the first structural cracking occurs.

The fibers also increase the compression behavior of concrete, especially by increasing the voltage on capacity. HPFRCs has shown to exhibit a very similar behavior in the confined concrete, load capacity exceeding 1%. This suggests that the confinement reinforcement relaxations are possible when using HPFRCs than concrete.

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FRP Rebar

Reinforced concrete is a very common building material for construction of facilities and structures. Complementing the strength of concrete in tension is very limited, the construction of steel structure was a cost effective solution. However, insufficient concrete cover, poor design or workmanship, and the presence of large amounts of aggressive agents, including all environmental factors can lead to cracking of concrete and corrosion of steel bars. For example, the United States, almost 40% of bridges are structurally deficient or functionally obsolete, and the percentage is increasing, according to the Federal Highway Administration (Griffiths 2000) For many years there have been many studies on this subject the corrosion, and the interest of FRP (Fiber Reinforced Polymer) has recently emerged as a potential substitute for steel. A careful examination of the potential of FRP reinforcing bars to meet cost and performance may propose appropriate solutions.

The benefits

* Waterproof to chloride ions and chemical attack

* Tensile strength than steel

* 1/4th weight of steel reinforcement

* Transparent to magnetic fields and radio frequency

* Electrically and thermally conductive

Based on the above characteristics, FRP bars appears to be a promising alternative to steel reinforcement in concrete structures such as marine structures, parking structures, bridges, roads in extreme environments, and structures are very sensitive to magnetic fields and corrosion.

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FRP Rebar – Technology

Recently, composite materials made from fibers embedded in a polymer resin, also known as fiber reinforced polymers are an alternative to steel reinforcement for concrete structures. Fiber reinforced polymer aramid (AFRP), carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (FRP) bars are the products commercially available for the construction industry. They have been proposed for use instead of steel or prestressed steel cables nonprestressed or prestressed concrete (ACI 440R 2006). The problems of steel corrosion is avoided with the use of FRP because fiber reinforced non-metallic materials are non-corrosive. Furthermore, FRP materials have several properties including high tensile strength which makes them suitable for use as structural reinforcement.

In addition, codes and design provisions have been recently developed guidance for the use of FRP bars in concrete structures for bridges and buildings (ACI 440H 2000, CSA 2000, ISIS-Canada, 2000).

The bond properties are responsible for transferring the load of concrete to strengthen and develop the necessary restraint in strengthening the balance, especially when the concrete is cracked. The service limits in FRP reinforced concrete elements, such as deflection, crack width and crack spacing is directly influenced by the properties of link reinforcement in concrete. Fiber reinforced polymer bars are anisotropic materials. Factors such as the type and amount of fiber and resin, fiber orientation and quality control during the production process plays a major role in the mechanical properties. If rebar carbon FRP (CFRP bar Isorod Pultrall, ADS Composites Group), when comparing a steel rod of 11.3 mm reinforced carbon fiber with a diameter similar about 9.5 mm, the results show that the tensile stress-strain curves of the CFRP bar is linear up to fracture (All FRP bars is linear elastic to failure).

The tensile strength of at least 1500 MPa, three times with reinforcing steel. The elastic modulus of the CFRP bar is 128 GPa, about 65% that of steel. CFRP bar set close to the bond strength to concrete even as a steel bar diameter 11.3 mm. (Benmokrane et al. 2001) As for glass FRP bars (GFRP bar ASLAN 100 Hughes Brothers, Inc.), tensile strength of 9 mm GFRP bar is 760 MPa and a modulus of elasticity is 40.8 GPa , much lower than for steel.

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About Fiber Reinforced Concrete

Reinforced concrete with steel fibers or synthetic fiber is known to reinforced concrete. Fiber reinforced concrete made an impression across the construction sector as being stronger, more malleable and more reliable than the cement alone. Fiber Reinforced Concrete has many uses and new applications are developing rapidly.

Fibre reinforced concrete is concrete that is mixed with synthetic fibers or steel. This concrete may also consist of steel and synthetic fibers in a mixture. The construction industry prefers fiber reinforced concrete on the regular strength and durability.

Fiber reinforced concrete is also known for its ability to control fire. Steel fibers in concrete and synthetics are less likely to break and crack when exposed to heat. There are currently several ongoing studies are currently evaluating the effectiveness of fires fiber reinforced concrete and extreme.

The most common use of fiber reinforced concrete is to make the factory floor. Fiber reinforced concrete is known to be able to withstand cold and heat, without cracking. Thus, fiber reinforced concrete is a viable alternative to the factory, because it takes the heat and pressure of the big machines.

Engineers and scientists are looking for fiber and to strengthen and improve the properties of concrete. They found an additive that makes the fiber concrete lighter and more resistant to cracking of the concrete alone. Additives are also working with natural fibers such as cellulose, which is trying to create a more environmentally friendly concrete.

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