Skip to content
Michael Z. Stern A field manual of difficult urban development
Subject index

Slender Towers and Supertall Engineering

Why a thin tower moves, how much movement people will accept, and the three levers that quiet it.
Michael Stern in a navy jacket and white shirt outdoors at dusk with a city skyline behind him

Supertall engineering is one of the five subjects Michael Stern works in, and the entries in this index treat its governing problem: a tower that is tall and narrow moves in the wind, and the motion troubles the people inside long before it troubles the structure. Wind reaching a bluff building separates at the corners and sheds alternating vortices into the wake, and when the rhythm of that shedding matches the frequency at which the tower naturally rocks, the sway grows. The B1M’s explainer sets out the shaping answers: softening or notching the corners, which cut movement at Taipei 101 by as much as a quarter, tapering as the Shard and the Petronas Towers do, stepping the profile with setbacks, twisting the floor plates as Shanghai Tower does, and opening the building so air passes through it.1

Shape alone rarely settles the question on a very thin plan. The structural engineer of 432 Park Avenue described in Structure magazine a square plan of 93.5 feet rising 1,396 feet, a slenderness of 1 to 15, and the combination that made it work: thicker slabs near the top to add mass, five two story open floors that break up vortex shedding, concrete of 14,000 pounds per square inch in the lower 38 stories for stiffness, and two 660 ton pendulum dampers near the crown to hold accelerations within the industry’s comfort limits.2 Each of those is a lever, and the entries explain what each one costs in floor area, in material and in money for the wider industry.

The field is still moving. A study reported by Newsweek proposes letting part of a tower’s own occupied floors act as the damping mass, and in wind tunnel tests the approach cut peak accelerations by up to 71 percent against a rigid tower, with the authors noting that conventional tuned mass dampers consume space and expense while doing little against the strongest winds.3 Engineers quoted in the same report call it promising rather than proven until a real building carries it.

The entries run from the measure to the remedy. Supertall Engineering, Slenderness Wind and Damping is the long pillar. What a Slenderness Ratio Measures defines the number. Occupant Comfort Criteria in Tall Buildings explains acceleration limits and return periods. Vortex Shedding and Across Wind Response covers why a steady moderate wind can trouble a tower more than a storm. Tuned Mass Dampers Explained, Wind Tunnel Testing for Buildings and the study of building shape against wind take the three remedies in turn. Damping, Stiffness and Mass in Tall Buildings weighs the levers against each other. Slender Towers Around the World gathers the cases, and How Height Is Measured in Tall Buildings explains the yardsticks.

  1. The B1M, How Tall Buildings Tame the Wind
  2. Structure magazine, 432 Park
  3. Newsweek, Skyscrapers sway in high winds. Engineers found an unexpected way to stop it

Contents

  1. A concrete tower core under construction in a desert landscape with cranes at its top, a Wikimedia Commons photograph in Michael Stern's encyclopedia Supertall Engineering, Slenderness Wind and Damping

    Slender towers answer to a quieter test than strength, and passing it has a price this entry puts in order.

  2. A very tall, narrow residential tower with a square grid facade against a clear sky, a Wikimedia Commons photograph in Michael Stern's encyclopedia What a Slenderness Ratio Measures

    A proportion of base to height, and the century in which its accepted limit moved from seven to one past twenty.

  3. An office tower with a sloped crown seen from above the surrounding rooftops, a Wikimedia Commons photograph in Michael Stern's encyclopedia Occupant Comfort Criteria in Tall Buildings

    The whole design of a narrow tower bends around one small number read off an accelerometer.

  4. A twisting glass supertall tower rising above a tree lined avenue, a Wikimedia Commons photograph in Michael Stern's encyclopedia Vortex Shedding and Across Wind Response

    A walk from the windy sidewalk to the swaying crown, following the air as it peels off the corners.

  5. A gold painted steel sphere suspended on cables inside a tall building, seen from an observation deck, a Wikimedia Commons photograph in Michael Stern's encyclopedia Tuned Mass Dampers Explained

    Two ways to hang a few hundred tons near the crown so that the building and the weight move against each other.

  6. A wooden wind tunnel model of a city block with buildings in red and natural wood, displayed in a museum, a Wikimedia Commons photograph in Michael Stern's encyclopedia Wind Tunnel Testing for Buildings

    Seven questions a design team asks before, during and after a scale model goes into the wind.

  7. Looking up the curved diagonal grid of a glass office tower, a Wikimedia Commons photograph in Michael Stern's encyclopedia How Building Shape Breaks Up the Wind

    Eight moves a design team can make to the silhouette so that the wind never finds the building's rhythm.

  8. A large sculptural damper mass hanging inside the crown of a tower, lit from above, a Wikimedia Commons photograph in Michael Stern's encyclopedia Damping, Stiffness and Mass in Tall Buildings

    Three dials on one equation, priced in concrete, floor area and machinery, turned in a set sequence.

  9. A tapering supertall tower rising above a river and a city skyline in haze, a Wikimedia Commons photograph in Michael Stern's encyclopedia Slender Towers Around the World

    One rule, the ratio, and the different ways New York, Hong Kong, Chicago and Melbourne have paid for it.

  10. Twin towers with pointed spires joined by a skybridge, seen from below, a Wikimedia Commons photograph in Michael Stern's encyclopedia How Height Is Measured in Tall Buildings

    Every tower carries three heights, a council referees them, and part of every skyscraper is space nobody can stand in.