Engineering Inc - November/December 2017 - 21

"Testing has
advanced
remarkably.
Today's
wind testing
methods-
which are
used on
virtually
every building
over roughly
400 feet-
are producing
truly
incredible
structures."

Of course, the end goal is a structure
that can withstand the forces of nature
and deliver maximum comfort. By
knowing how wind and structure
interact, a design team can increase
the efficient use of materials, trim
unnecessary costs and risks, and
deliver a reliable design. "While it's
possible to toss unlimited concrete
and steel at structures, the idea is to
build something that is elegant and
functional. It should fit the physical
environment but also be adapted for
that place. It isn't just about designing
to withstand anything. It's about
designing and engineering in the
most effective way possible, which
encompasses creative design, costs,
environmental factors and safety," says
Banks.
SKY'S THE LIMIT

Not every large bridge and building
requires sophisticated climatological
data and extensive wind tunnel testing. Brent Wright, president of Wright
Engineering in Columbus, Georgia,
says industry standards that address
wind design are adequate for building
many structures. They provide basic
information and guidelines about wind
loads and construction standards. He
typically consults the standards for
constructing schools, offices and other
ROBERT SINN buildings. This leads to the installation
THORNTON
TOMASETTI of shear walls, braced frames, different
types of windows or other basic modifications. "Additionally, most buildings
simply require components to withstand uplift loading," he says.
Yet, the wind engineering that goes into the tallest and
most sophisticated structures is remarkable. For instance, the
1,667-foot-tall Taipei 101 tower, once the world's tallest building, and a 2006 EEA Grand Award Winner featuring structural
design by Thornton Tomasetti, uses a 727-ton tuned mass
damper to harmonically absorb wind motion. The sphere is 18
feet in diameter and is suspended between the 87th and 92nd
floors. It was actually tested during Typhoon Soudelor in 2009.
When winds hit 145 mph, the giant orb swung more than 1
meter horizontally. The building did not sustain any major damage from the storm.
Make no mistake, wind engineering results in better architecture, engineering and construction methods. While it's
impossible to build a bridge or a building that is completely
windproof, today's methods maximize public safety while driving design excellence and cost savings. "Testing has advanced
remarkably. Today's wind testing methods-which are used on
virtually every building over roughly 400 feet-are producing

Wind Testing the World's Tallest Building
When Burj Khalifa was completed in 2010, it became the
world's talent skyscraper, rising to a height of 828 meters
(2,716.5 feet). The mixed-use structure-which includes a 304room hotel, 900 apartments and office spaces-has emerged
as one of the most identifiable buildings in the world.
Understanding wind loading and wind-induced motions
was critical. The tall and slender shape of the building added
to concerns. Although engineers had designed the core of
the structure as a bundled tube and a Y-shaped design was
selected to "confuse the wind," extensive wind testing was
required using 1:500 scale models and a 1:50 model for the
top one-third of the building.
RWDI embarked on a series of wind tunnel tests at its
Guelph, Ontario, facility. Teams used high-frequency force
balance to understand crosswind effects of vortex shedding
on the building. Along the way, designers changed the design
of Burj Khalifa-including the number and spacing of the
setbacks.
By overlaying wind tunnel tests with climate data, architects and engineers ultimately determined that it was best to
reorient the tower to greatly minimize the effects of the wind.
Using rigid-model force balance tests, full multi-degree-offreedom aeroelastic model studies, measurements of localized pressures and pedestrian wind environment studies, they
also found ways to minimize winds in pedestrian areas and
observation decks.
RWDI

A model of Burj Khalifa placed in a
wind tunnel for testing at RWDI.

truly incredible structures," says Sinn, chief structural engineer
for Jeddah Tower. This allows architects and engineers to move
beyond box high-rises and simple bridges and introduce far
more innovative and beneficial designs. n
Samuel Greengard is a technology writer based in West Linn, Oregon.

NOVEMBER / DECEMBER 2017

ENGINEERING INC.

Table of Contents for the Digital Edition of Engineering Inc - November/December 2017