Structural performance and economics of tall high strength RC buildings inseismic regions

For a multitude of economic and societal considerations, high rise structur es are on the increase. This in turn promotes the use of high strength mate rials to reduce column size and construction times. 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. In this paper, 10 buildings of 24 stories are designed and detailed according to m odem seismic codes. The buildings are all nominally equivalent, using a sti ffness equivalence criterion and its derivatives. The cost of construction is compared in terms of steel, concrete and formwork. The static inelastic response of the buildings is also assessed, followed by a full nonlinear dy namic analysis of all buildings using three earthquake records at the desig n acceleration and twice the design value. Comprehensive assessment of the static and dynamic results is undertaken. It is concluded that the cost inc rease is mainly due to the steel, whilst significant member reductions may be availed of by using high strength concrete. The behaviour of high streng th concrete structures is not inferior to that of normal strength materials . Indeed, it is observed that lower levels of overstrength can be achieved in high strength materials than in their normal strength counterparts, main ly due to the over-reinforcement of the latter to resist vertical forces. R ecommendations on the use of equivalent cracked stiffness for period calcul ation in design, and also effective periods for use in displacement-based d esign, are given. Copyright (C) 1999 John Wiley & Sons, Ltd.