A number of additional economical benefits stem from the use of CFTs. The tube serves as formwork in construction, which decreases labor and material costs. In moderate- to high-rise construction, the building can ascend more quickly than a comparable reinforced concrete structure since the steelwork can precede the concrete by several stories. The cost of the member itself is much less than steel and roughly equivalent to reinforced concrete on a strength per dollar basis for low to medium strength concrete (Webb, 1993). When compared to steel moment resisting frames, in unbraced CFT frames, the amount of savings in steel tends to grow as the number stories increases (Morino et al., 1996).On the other hand, relatively simple beam- to-column connection details can be utilized for rectangular CFT members. This also results in savings for the total cost of the structure and facilitates the design process. In addition, the steel tube and concrete act together to provide natural reinforcement for the panel zone, which reduces the material and labor costs of the connections. With the use of high-strength concrete, CFTs are stronger per square foot than conventional reinforced concrete columns (Webb, 1993).In high-strength applications, smaller column sizes may be used, increasing the amount of usable floor space in office buildings. The smaller and lighter framework places less of a load on the foundation, cutting costs again. These advantages have secured an expanding role for this versatile structural element in modern construction.
A primary deterrent to widespread use of CFTs is the limited knowledge regarding their behavior. A number of factors complicate the analysis and design of concrete-filled steel tubes. A CFT member contains two materials with different stress-strain curves and distinctly different behavior. The interaction of the two materials poses a difficult problem in the determination of combined properties such as moment of inertia and modulus of elasticity. The failure mechanism depends largely on the shape, length, diameter, steel tube thickness, and concrete and steel strengths. Parameters such as bond, concrete confinement, residual stresses, creep, shrinkage, and type of loading also have an effect on the CFT’s behavior. Axially loaded columns and, in more recent years, CFT beam-columns and connections, have been studied worldwide and to some extent many of the aforementioned issues have been reconciled for these types of members. However, researchers are still studying topics such as the effect of bond, confinement, local buckling, scale effect, and fire on CFT member strength, load transfer mechanisms and economical detailing strategies at beam-to-CFT column connections, and categorization of response in CFTs and their connections at all levels of loading so as to facilitate the development of performance-based seismic design provisions. It should also be noted that, despite a recent increase in the number of full-scale experiments, the majority of the tests to date have been conducted on relatively small specimens, often 6 inches in diameter or smaller (see Tables 1 through 6). This is due to the load limits of the testing apparatus and the need to run the tests economically. Whether these results can be accurately extrapolated to the typically larger columns used in practice remains a pertinent and debatable question, although recent research in Japan has begun to address this important issue (Morino et al., 1996).
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只看楼主 我来说两句 抢板凳一小学的阻吓作用,广泛使用cfts是有限的知识,对于他们的行为。多项因素影响,复杂的分析与设计钢管混凝土。 1打击资助恐怖主义的会员包含两种材料具有不同的应力应变曲线和截然不同的行为。相互作用的两种材料构成的一个难题,在确定合并属性,如转动惯量和弹性模量。失效机理在很大程度上取决于形状,长度,直径,钢管的厚度,混凝土与钢的优势。参数,如债券,具体的隔离,残余应力,蠕变,收缩,和类型的负荷也有一个作用,对打击资助恐怖主义的行为。轴心受压柱和,在最近几年,钢管混凝土压弯构件和连接,已研究了世界各地,并在一定程度上上述许多问题已得到调和,对于这些类型的成员。不过,研究人员仍在研究等课题的影响,债券,隔离,局部屈曲,规模效应,及消防对打击资助恐怖主义的会员力量,负荷转移机制和经济,详列战略束到钢管混凝土柱连接,及分级反应的cfts和他们联系,在所有各级装货,以便发展基于性能的抗震设计的规定。还应当指出,尽管最近的数目有所增加,全规模的实验,大部分的测试,到目前为止已进行了对相对较小的标本,往往是6英寸,直径或更小(见表1 ,通过6 ) 。这是由于负荷范围内的测试仪器和需要运行测试,在经济上。是否这些结果可以准确地推断典型的大柱用在实践中仍然是一个相关的和值得商榷的问题,虽然最近的研究在日本已开始处理这一重要问题(森野等人, 1996年) 。
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