![]() It is their deformation characteristics that should be carefully studied from an earthquake resistance viewpoint. Therefore, the fact that new construction materials may offer higher strength to the designer than conventional ones should not be a comforting thought. The combined effect of the three above- mentioned requirements renders high strength concrete economics rather appealing.Modern seismic design codes require the designer to ‘identify’ sources of energy absorption and ‘quantify’ their energy absorption capacity in a response range through which no collapse will occur. Moreover, the need for rapid construction requires early age strength gain, a feature that may be offered readily by high strength concrete. Increased wind and traffic vibration susceptibility dictates that the modulus of elasticity of the material should be as high as possible in order to limit small amplitude elastic displacements. Two other performance criteria lend weight to the argument for the use of high strength concrete (HSC). Historical evolution of building heightdimensions and to make more effective use of floor areas, especially in the lower storeys of high rise structures. Elnashai, Department of Civil and Environmental Engineering, Imperial College, Imperial College Road, London, SW7 2BU, U.K.172 B. The historical development of building height is shown in Figure 1.The need for higher buildings naturally leads to the conclusion that high strength construction materials will be increasingly used in the future, in order to keep column sizes at manageable* Correspondence to: Professor Amr. Examples of such projects are the Akashi-Kaikyo Bridge linking Kobe City to Awaji Island (length 3910 m) and the Petronas Towers in Kuala Lumpur (height 450 m). A secondary stimulus for construction of high rise buildings is that of an engineering challenge, whereby the two targets of boasting the longest bridge and the highest building have become serious considerations in the conceptual design of landmark projects. Whereas in 1950 there were only 7 urban areas in the world with more than 5 million inhabitants, this number rose to 34 in 1980 and is expected to rise further to 60 by the year 2000.1 Consequently, more high rise structures are being constructed now than a decade or two ago. High rise buildingsThe increasing reliance of employment on financial services is one of the reasons that lead to increasing rural-to-urban migration which in turn lead to increased demand on land use in large cities. Recommendations on the use of equivalent cracked stiffness for period calculation in design, and also effective periods for use in displacement-based design, are given. Indeed, it is observed that lower levels of overstrength can be achieved in high strength materials than in their normal strength counterparts, mainly due to the over- reinforcement of the latter to resist vertical forces. The behaviour of high strength concrete structures is not inferior to that of normal strength materials. It is concluded that the cost increase is mainly due to the steel, whilst significant member reductions may be availed of by using high strength concrete. Comprehensive assessment of the static and dynamic results is undertaken. The static inelastic response of the buildings is also assessed, followed by a full nonlinear dynamic analysis of all buildings using three earthquake records at the design acceleration and twice the design value. The cost of construction is compared in terms of steel, concrete and formwork. The buildings are all nominally equivalent, using a stiffness equivalence criterion and its derivatives. ![]() In this paper, 10 buildings of 24 stories are designed and detailed according to modern seismic codes. Whereas design guidance and engineering understanding of high strength RC structures under static loading is well-developed, little work has been undertaken on the economics of whole buildings and their performance under earthquake loading. This in turn promotes the use of high strength materials to reduce column size and construction times. ELNASHAI*Department of Civil and Environmental Engineering, Imperial College, London, U.K.SUMMARYFor a multitude of economic and societal considerations, high rise structures are on the increase. 8, 171–204 (1999)STRUCTURAL PERFORMANCE AND ECONOMICS OF TALL HIGH STRENGTH RC BUILDINGS IN SEISMIC REGIONSBENEDICT T. THE STRUCTURAL DESIGN OF TALL BUILDINGSStruct.
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