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Reinforced concrete is a type of modern material which includes imbedded metal bars, rods, wires or other slender members and the concrete acts together with metal in resisting forces (the concrete resists compression and the metal resists tension). Owing to the inherent advantages of concrete and the metal, reinforced concrete is widely used by engineers and architects to build residential buildings for over a century. Dramatically, reinforced concrete was not invented by engineers. It was invented by Joseph Monier (1849), a Parisian gardener who made garden pots and tubs of concrete reinforced with an iron mesh. After the invention, reinforced concrete provided much more choices for engineers to design structures and leaded an improvement of construction industry throughout the world. In this essay, the benefits and drawbacks of reinforced concrete will be discussed and compared it with other building materials, such as timber, concrete, brick and stone. In 21st century, reinforced concrete has caused many problems. However, it is still vitally important for engineers and cannot be replaced by other building materials easily.
Before the reinforced concrete was invented in 19th century, stone, timber, concrete and glass were used to construct buildings and those materials have serious weaknesses in several aspects, such as fire resistance and seismic behavior. However, the reinforced concrete could overcome most of these weaknesses. Compared with the buildings made by woods, engineers believe that the main advantage for the buildings made by reinforced concrete is that they are less dangerous when in a big fire. Stollard and Abrahams (1999) studied the fire resistance of several building materials. In these people's study, the oversize timbers could resist the fire under 350â„ƒ. If the temperatures on the surface exceed 350â„ƒ, the wood would burn and the charring rate may change from 0.5mm/min to 0.83 mm/min (Stollard and Abrahams, 1999). As a result, in order to make the structure safe, the engineers have to design the building by using timber elements which are artificially oversized and the cost of the project would be increased dramatically. However, as Stollard and Abrahams (1999) have indicated that the reinforced concrete can easily resist the fire for 4 hours (Stollard and Abrahams, 1999). Owing to this, the safety of reinforced concrete residential buildings indeed exceeds the timber buildings.
Apart from the research of Stollard and Abrahams, the methods used to improve structural fire resistance of the reinforced concrete are quite advanced. Huge amount of fire-testing researches and analysis have been directed towards fire resistance techniques applicable to reinforced concrete structures. Fitzgerald (2004) notes that the well designed fire barriers could largely improve the safety of reinforced concrete building (Fitzgerald, 2004). For example, the fire barriers can protect people from combustion products while they remain in the building and wait for rescue. Furthermore, by changing the design of the building, the engineers can improve the reinforced concrete building's durability in the fire, such as, increasing the thickness of surface concrete covers (Reynolds, C. E., Steedman, J. C. and Threlfall, A. J., 2008).
The second reason that some engineers support that reinforced concrete cannot be replaced easily is that it has excellent performance during the earthquake. This characteristic is extremely important when the buildings are constructed in the regions having frequent earthquake. In general, the damage to buildings varies to a great extent with the building's ability to dissipate energy and dampen the vibration during an earthquake. To resist the earthquake, the engineers put the reinforced concrete shear walls in high-rise residential buildings and normal residential buildings. This wall can absorb a great deal of energy during the earthquake to make the structure safe. A study by Penelis and Kappos (1997) shows that as the earthquake happens, the shear force is relatively high. This may require unusually large structural members especially in the lower floors. Thus, the reinforced concrete shear wall can be considered as a best solution for carrying the shear force generated by earthquake (Penelis and Kappos, 1997). In contrast, a devastating earthquake hit Tangshan, which is a city of China, in 1976. The entire city was ruined and over 200,000 people died in this disaster. The reason why the whole city was destroyed is that the buildings were constructed by brick, concrete and stone. Therefore, the reinforced concrete may be the best choice to build the city to make the citizens safe.
In additionï¼ŒReinforced concrete structures have the potential to be very durable and capable of withstanding a variety of adverse environmental conditions. To be more precise, the service life of reinforced concrete is long (usually more than 75 years) and having low maintenance cost. Generally, it is easy to meet the construction code's demands in different countries. For example, the China's technical specification for reinforced concrete structures requires that the residential buildings must be used no less than 75 years. Besides, if the reinforced concrete residential buildings were not struck by powerful earthquake, it almost do not need repair or retrofit during the 75 years. So the maintenance cost is extraordinary low. According to Morinaga's (1991) research, there are two major factors, which cause corrosion of reinforcement in concrete to proceed to an unacceptable degree and as a result, the service life of the building was reduced. However, the corrosion works at a low steady rate. Therefore, the service life is easy to reach the Code's request (Morinaga, 1991).
However, the reinforced concrete indeed has some drawbacks in terms of environmental impact and quality control. As Mehta (2001) indicated that manufacturing one ton of portland cement, which accounts for 12% of concrete, consumes about 4 GJ energy and generates approximately 1ton greenhouse gas (carbon dioxide) into the environment. 'For global concrete making, we are consuming portland cement at the rate of 1.6 billion tons every year' (Mehta, 2001). As a result, reinforced concrete industry impacts the environment hugely. Furthermore, about 1 trillion L fresh water was used by the concrete industry every year (Mehta, 2001). This large amounts of fresh water can support many people's daily life. Additionally, the quality control of reinforced concrete is not easy to do. It usually needs electrochemical techniques equipment which is expensive and hard to inspect all of the main structure. Thus, the engineers cannot make sure that the whole structure has met the Code's standard.
Taking all the factors above into account, despite that reinforced concrete seems to have some weaknesses during the construction today, it is of course true that most residential buildings can succeed with reinforced concrete. Furthermore, the material alone is not enough to guarantee that the reinforced concrete residential buildings will survive from a huge earthquake or fire. It must have smart engineering and be well built and well designed if you wish for the building could through the hardest hits. The last thing to be aware of is that at times, if the disaster was one of the most powerful kinds, the choice of reinforced concrete residential building would not make people safe as well. Fortunately, these types of disasters are very rare and hopefully, it will not happen in your lifetime.
To conclude, the reinforced concrete is the key material in construction today. Though it has some drawbacks, it is not easy to be replaced in a short period. (Word Count =1203 words)