Aerodynamic performance of tall buildings: a study on the relation between wind escape and outrigger floors

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2019
Aksu, Yeliz
Numbers of slender tall buildings, particularly “super-slenders”, are increasing rapidly due to the quest for maximizing the leasable space in plan or being iconic or both. With their relatively short structural depth in plan, limiting the top drift, in other words, satisfying the serviceability limit is usually the governing constraint in their design. Using multi-level outriggers, tuned mass dampers and distinctive aerodynamic modifications such as wind flow openings together is rather mandatory to realization of such designs. However, there is a trade-off between outrigger system and wind escape floor if they are located at the same level. The outriggered-frame structural system gives the building its stiffness whereas openings as wind escape floors are aerodynamic modifications for decreasing the wind load acting on building. This study evaluates the interrelation of outriggers and wind escape floors arranged at the same floor level in terms of several structural response parameters. The relationship between openings as aerodynamic modifications for mitigating the wind loads and outriggers (including virtual outriggers) in slender tall buildings have been investigated with the aim of improving the building performance in the context of top drift limitation and reduced wind loads. The research question is the possibility of having less number of outrigger floors by taking the advantage of wind escapes which have located at the outrigger floors without sacrificing occupant comfort. In other words, if the top drift of a building which has a certain type and number of outriggers organized with wind openings can be kept less than the top drift of a building having more outrigger floors with closed façades, then the architects and engineers may prefer the combined use of outrigger floors with wind escape floors to increase leasable plan area. An existing super-slender building having both outriggers and wind flow openings at mechanical floor levels has been selected and alternative outrigger and wind flow opening configurations have been modelled on this sample building. Then comparisons have been made to scrutinize the optimum use of outriggers with wind openings. Top drift, story shear and moment, particularly core moment, have been used as demand parameters in this study. The results showed that the optimum use of wind openings with certain type of outriggers can yield better structural response to wind loads compared to closed façade building having more number of outriggers. Code based wind loading without vortex shedding effects can be counted as limitations of the study. Thus, wind tunnel testing of promising outrigger wind escape floor arrangements identified in this study can be conducted as future remarks.

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Citation Formats
Y. Aksu, “Aerodynamic performance of tall buildings: a study on the relation between wind escape and outrigger floors,” M.S. - Master of Science, Middle East Technical University, 2019.