ABSTRACT
Dynamic properties, aerodynamics, placement of structural materials, floor-to-floor heights, and aspect ratios are all important characteristics in maximizing structural efficiency of the tall tower. The aerodynamics of the tall tower are important in minimizing imposed design forces. Across-wind motion governs the behavior of the structure. Organized vortex shedding generates the highest forces levels. Vortex shedding is most organized with circular cross-sectional shapes, less organized with triangular shapes, and least organized with square shapes. The introduction of holes through the building cross-sections improves the behavior further. Variation of the structure's cross-section along its height also acts to disorganize or disseminate vortex shedding. Strouhal numbers describe oscillating flow mechanisms and are based on the frequency of vortex shedding, shape geometry, and wind velocity. Typically, buildings with aspect ratios greater than 8 to 1 should consider supplemental damping systems to reduce occupant perception to motion.
