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A Study on the preliminary design of tall buildings: investigating structural components

Çamlıbel, Gülçin
Tall buildings are built to respond to limited and high-cost urban land problem, and they became essential for urbanization which changes the sights of the cities. These buildings are huge investments, and keeping Net Floor Area (NFA) within acceptable limits while satisfying stiffness and strength requirements of the building is important; therefore, different structural systems are improved in order to overcome huge lateral load demands. Since simple design approaches and rule-of-thumb dimensioning methods based on conventional structures and loads cannot be adapted to tall buildings, tall buildings, particularly supertall buildings which are more than 300m in height requires a long and repetitive planning phase before structural and architectural design. The aim of this study is to provide the approximate dimensions of the structural components, particularly core and columns, of tall buildings for preliminary design phase by investigating existing buildings. For this purpose, a database of tall buildings which is obtained from existing buildings is created and corresponding statistical analysis results are presented. At the first stage of the study, a literature survey has been conducted in order to determine the structural design considerations of tall buildings. According to these considerations, identity parameters, architectural parameters and structural parameters are specified and collected for as much existing buildings as possible. Important parameters such as aspect ratio, core area and column area have been calculated, and special features such as dampers and wind openings have been detected. Structural system details of outriggered frame buildings such as outrigger height and number of outriggers have been investigated. Regarding the collected information, statistics on preliminary design variables of tall building’s structural systems have been presented. According to the analyses, core area and column area ranges of tall buildings are given for outriggered frame, tube and shear frame structural systems and for specific regions. The results showed that, shear frame system is the least efficient structural system whereas outriggered frame system is as favored as tube system in terms of net floor area. The results showed that, for preliminary design of a tall building regardless of its structural system, location, structural material or height, 27% and 3% can be taken as conservative central values of core and column area ratio, respectively. Minimum, maximum and average values of ratios of core area to floor area and total column area to floor area are provided with respect to alternative structural system of tall buildings. The results of this study can be easily used by architects and engineers in the preliminary design stage of tall buildings.