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A comparative study on alternative structural system layouts of twisted tall buildings

Taşkın, Gökçe Nihan
Tall buildings are seen as icons in their environment and they have a strong impact on the silhouette of the cities. The form of a tall building is critical to define an iconic expression and control their impact on the city silhouette in an aesthetically desired way. In this respect, designers are searching for diversity and uniqueness in the form of tall buildings. Twisted forms are one of the answers for this quest. However, the inherent complexity of twisted tall buildings can pose adverse design features. This study aims to evaluate the challenges of twisted forms in terms of architectural and structural design. First, architectural and structural features of existing examples of twisted tall buildings are examined in terms of their plan layouts, modelling and constructing process, aerodynamic performance, lateral stiffness and torsional demands. Then, generic twisted tall building models are created. The height, structural system and angle of twist of these models are defined such that, the resulting configurations represent the existing buildings as much as possible and provide the opportunity to analyze effect of these features on architectural and structural design in a controlled way. In this study, mainly two alternative structural system layouts called as “adaptive” and “non-adaptive” are compared. Besides, a third case named "adaptive-inside" is examined only once. In non-adaptive case, columns stand parallel to the gravitational acceleration as in the case of conventional structures. To create the twisted form, the floors are rotating around the center of the mass by a certain angle on each level but the columns aren’t. In the structurally adaptive case on the other hand, both the structural system and the floors are rotating with the same twist angle which make the columns be leaned to some extent. Adaptive-inside case has a twisted structural system similar with adaptive case but the structural depth of the system is equal to the non-adaptive case's structural depth. Computer models are created and structural analyses and design checks are performed in ETABS software. Top displacement and structural member forces are of primary concerns in this study where base reactions and modal characteristics have been investigated as well. The results are compared and discussed to evaluate the effects of building height, structural system and angle of twist on the efficiency of adaptive and non-adaptive structural system layouts.