Coursework 1 - Coursework 1 Zhewen, Chen 07 Civil...

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Coursework 1 Zhewen, Chen 07 Civil Engineering 1.(a) Compare the uses of structural steelwork and reinforced concrete in the construction of high-rise building with particular reference to strength/ weight ratio , speed of construction , cost, and fire and corrosion protection requirements. (1).strength/weight ratio: Comparing with ordinary reinforced concrete, structural steelwork has a higher strength/weight ratio. Steel is strong both in compressive strength and tensile strength, while concrete is quite strong in compressive strength but weak in tensile strength. The density of steel is about 7850kg/m 3 and the characteristic strength of steel can be more than 400Mpa.The weight of concrete is largely depends on the kind of aggregate we choose. If we use lightweight aggregate to make concrete, the density can be as low as 1600kg/m 3 .But lightweight concrete is not suitable for building high-rise building because it is relatively weaker than original Portland cement concrete. So we usually use it to make something that isn’t expected to carry loading, such as structure brick walls. In high-rise buildings we prefer to apply high-strength concrete which is able to carry much more loading than normal concrete. Today, high-strength concrete can even reach grade 100 in laboratory. With so high strength concrete, we can offer the minimum amount of steel . In this way, we can find the most economical methods for columns in high –rise building. Actually, using high-strength concrete, we can reduce the cross sectional size of
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columns, thus allowable more usable floor space, which seems very significant to the area where the price of land is quite expensive. Moreover, the heat produced during water-cement hydration can escape a lot easier. (2) .speed of construction : Getting a building completed and occupied as quickly as possible by rent-paying tenants is important to a developer so that construction speed is a major consideration . In theory using steel is faster than concrete because when using steel we just have to weld them or bolt them together while we use concrete instead we need to wait for several days before it can be left there without any curing . With concrete, we can have a “ fast track ”, which means we can start construction even when the design of the whole structure is only partially done and get the building completed sooner. With a steel frame, on the other hand, the entire design must be completed before we can work on the construction, and we may have to wait for several months before the steel structure is fabricated and shipped to the job site. On the other hand, we can get concrete from a much nearer place, sometimes just 50~100km away(actually we can even make concrete even on job site)so we can get concrete more quickly , and even immediately. In fact we usually have a 3-day- cycle in HK when we use concrete to build high-rise buildings. Someone will argue that concrete should cost longer time because we need to spend some time
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Coursework 1 - Coursework 1 Zhewen, Chen 07 Civil...

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