The Future of Slender Tower Design

Mary Casey
Director, Social Infrastructure
HKA, Sydney

As urban centers run out of large lots ripe for development, towers have grown taller and ever more slender. Aspect ratios of 15 to 1 once pushed the technical limits and financial feasibility of tower development. New supertall towers have exceeded aspect ratios of 20 to 1. This slenderness, in some cases coupled with climate change, results in vortex shedding effects driving tower motion at lower wind speeds and more frequent recurrence intervals.

Common damping technologies are stretched to control tower movements, and in some cases forced height reduction has occurred to bring movements in line with those that the dampers can tackle. Integrated damping technologies offer the potential to more effectively control motions for slender towers while providing significant space and cost savings. However, a change in the way that damping is currently designed and procured is required.

Elevated heights and slenderness ratios bring new challenges for the structural design of these supertall towers. Second order effects and nonlinear material behavior can drastically magnify loads, affect dynamic wind interaction, and alter load paths in the structure. Traditional methods to estimate structural performance can be more of an art than science and require significant judgement on the part of the engineer. Recent advances in nonlinear modelling capabilities combined with digital automation of workflows between linear and nonlinear modelling software has opened up opportunities to tackle age old tall building design problems in efficient and clear ways.

Advanced analysis techniques and integrated damping are the future in design for ensuring structural performance of these impossibly slender towers.

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