By John Leckie
Company Profile: Wind Experts ExtraordinaireEngineering
In its beginnings, the firm of Rowan Williams Davies & Irwin, known as RWDI, developed from the work of University of Guelph professor Frank Theakston and his students. Theakston had developed wat...
In its beginnings, the firm of Rowan Williams Davies & Irwin, known as RWDI, developed from the work of University of Guelph professor Frank Theakston and his students. Theakston had developed water flume technology, which uses fine sand and flowing water to simulate ground level winds and drifting snow conditions and was using it to provide consulting services to clients. In 1972, he joined forces with Bill Rowan, P. Eng. of the Toronto engineering firm of Morrison Hershfield Burgess & Huggins to form Morrison Hershfield Theakston & Rowan (MHTR), providing snow studies from its Guelph location.
As the firm expanded, the need for a boundary layer wind tunnel to carry out more extensive wind research became more apparent. Fortunately, about that time, the University of Toronto decided to dismantle one of its wind tunnels and it became available at a reasonable price. The addition of the wind tunnel opened up huge opportunities for the firm.
Following an amicable separation from Morrison Hershfield, RWDI came into existence in 1982 with Bill Rowan at the helm as president and chief executive officer. When Peter Irwin, P. Eng. took over the role in 1999, Rowan had been leading the firm for 27 years.
Over the decades RWDI has built up an international clientele. The company has helped on many signature projects around the world: office towers, sports facilities and community developments. Today, the company has 400 employees, including not just engineers, but also scientists, meteorologists, modelers and other specialists. Besides wind engineering, they cover environmental air quality, acoustics and building envelopes. The firm has seven offices in Canada and branch offices in the United Arab Emirates and India.
A sister firm, Motioneering, was formed in 2000 specializing in structural damping system designs and installation, as well as building retrofits and structural monitoring. RWDI has four boundary layer wind tunnels, two in Guelph, one in Miami and the fourth in Dunstable, U. K., as well as model shops and advanced computational fluid dynamics computing expertise.
Michael Soligo, who took over as president and chief executive officer from Peter Irwin last year, says the philosophy of the firm has remained constant over the years.
“We look at how we can help the designers and developers work with the environment to produce a high quality project or development with minimal impact on the environment,” he says. “Some of the tools we use and some of the approaches we use are different, but the philosophy hasn’t changed.”
“We have a good client base. We have focused on working with the top people in the field whether it is architectural development, or structural or mechanical engineering.”
Following are just three high-profile projects from the firm’s recent portfolio, where RWDI acted as a specialist consultant.
Burj Dubai, United Arab Emirates
Bill Baker, the chief structural engineer for Skidmore, Owings and Merrill, has said that Burj Dubai, destined to become the tallest building in the world at well over 700 metres in height, was virtually designed in the wind tunnel. (The actual height is a closely held secret to ensure it will be the world’s tallest building when it is completed in 2009.)
“On a building of this height and magnitude, the wind loads can really be the governing load for the horizontal loads on the structure,” says Peter Irwin of RWDI. “You are getting into a different game once you get beyond 70 or 80 storeys. When you are talking about 160 storey buildings or even 200-storey buildings, the wind engineering becomes an absolutely critical part of the overall feasibility.”
As a result, RWDI was involved in the Burj Dubai project from its early days. In extensive wind tunnel testing, they discovered the shaping that would reduce wind loads to a minimum and suggested reorienting the tower to obtain a more favourable alignment with the direction from which most of the strong winds flow.
Irwin estimated the wind tunnel testing saved many millions of dollars in structural costs.
The firm also carried out aeroelastic testing to ensure the building motions would not make people uncomfortable. Unlike many tall buildings, the Burj Dubai does not have a supplementary damping system.
The large cranes operating at the top of the building add to the wind load during the construction period. Another phenomenon that affects mostly tall buildings is vortex excitation, where wind vortices are shed from one side of the tower and then from the other. This can cause a fluctuating force to act on the building with a frequency that changes with the wind speed. It is possible for tall buildings to go into resonance with some of these frequencies, which could cause severe oscillations in the building.
The design of the Burj Dubai, which changes shape as it rises, solved the problem because vortices are trying to shed at different frequencies all the way up, which prevents any problem developing.
“We’ve worked on other buildings where it became a major issue and they have actually had to change the shape of the building to make it work,” Irwin says.
Wind tunnel testing also looked at conditions for people walking outside the building at ground level and also at higher levels on the many outdoor terraces.
“We helped develop some mitigation devices up there, improving the geometry of the edge parapets and putting up screens to make them [the terraces] usable for a greater fraction of the time.”
To measure the effects of wind and storms on the 700-m high building, RWDI developed special computer simulation models using software similar to that used for weather forecasting, and recreated major storms that have hit the area.
Stack effect is something that is familiar to most building scientists. Only in Dubai, it is the reverse of what it is in Canada.
“The temperature outside in Dubai can be 45 degrees Celsius or more,” Irwin says. “Inside, the buildings may be kept about 22 degrees. The large temperature difference causes the air inside the building to be much heavier than outside and makes it want to slump out the bottom of the building.”
Whether the air is moving to the bottom of the building or the top (as it would be in Canada where the inside air is usually warmer), there are some predictable mitigating factors that can be put in place.
Developer: Emaar Properties. Architect and engineer: Skidmore Owings and Merrill.
Pearl River Tower, Guangzhou, China
The design of the 71-storey Pearl River Tower, future headquarters for the China National Tobacco Corporation, is an attempt to create “the world’s most energy efficient highrise structure,” according to its U. S. architect and engineer, Skidmore Owings and Merrill (SOM).
The building’s features include the use of wind turbines, solar energy panels and other sustainable elements and characteristics.
For RWDI, the project also represents an indication of where the company is headed, beyond wind engineer into the realm of sustainable design. Part of the firm’s involvement is its traditional role of looking at the wind loading and its effect on structural and cladding design, as well as pedestrian comfort. But another role was to work with the design team at SOM to come up with efficient energy and ventilation systems for the building.
The team determined the configuration of the faade as a way to control the energy use in the building, says RWDI principal and director of the project Ray Sinclair. “We looked at the climate in the area and how that would interact with the building in terms of the faade and the heat coming in.”
The all-glass building features a transparent outer faade of double-paned glass; an interior cavity with blinds to mitigate solar radiation getting in, and then an interior layer of glass. The building uses a radiant cooling system.
Wind turbines have just started to appear in buildings in the pas
t couple of years. On this building, RWDI provided advice on shaping the wind portals and the position- ing of the turbines to gain maximum benefit from the available wind.
Owner: CNTC Guangdong Company. Architect: Skidmore Owings & Merrill. Structural engineering: Skidmore, Owings and Merrill.
Grand Canyon Skywalk, Arizona
The Grand Canyon Skywalk is a spectacular horseshoe-shaped glass walkway 1,200 metres above a side canyon near the Colorado River. Owned and operated by the Hualapai Tribe, the structure is in Grand Canyon West in northwest Arizona (not part of the Grand Canyon National Park).
Completed in 2005, the Skywalk presented a number of challenges for RWDI and its sister company, Motioneering.
The walkway’s structure consists of a pair of 2-ft. wide x 6-ft. deep structurally independent steel box beams, connected by a glass floor.
RWDI discovered as a result of a vibration analysis that the right combination of visitors walking or jumping on the skywalk could result in motion that might cause people unease.
“When you are walking on a glass floor about 4,000 feet above the canyon floor, you don’t want to be uncomfortable,” says Guy Ferguson, P. Eng., an RWDI project manager who worked on the project.
Motioneering developed a damper system that works like a shock absorber to keep the movement within comfortable levels.
“It is essentially a mass of steel that rides up and down on a central post,” says Ferguson. “When you get vertical motions induced by pedestrians, the mass responds by moving out of phase with the motion of the pedestrians and it strokes a viscous damper which converts mechanical motion into heat. It takes the energy out of the system so the amplitudes never grow to a big enough amount where people start to get concerned.”
The system consists of three 1.6-ton, tuned mass dampers –two near the apex of the outer box beam and one at the apex of the inner box beam. Because the size of the box beams was kept to a minimum to maximize the view, the dampers were a tight fit.
According to the Grand Canyon Skywalk’s official web-site, the glass bridge can withstand the weight of 71 fully loaded Boeing 747 airplanes and winds in excess of 100 miles per hour from eight different directions.
Owner: Hualapai Indian Tribe. Developer: David Jin. Architect: Mark Johnson, MJR Architects. Structural engineer: Lochsa Engineering.
Following are just a few of the high profile and more unusual projects RWDI has worked on besides the three featured in this article:
Freedom Tower (World Trade Centre site), New York City
Moscow City Tower, Russia
Taipei 101, Taiwan
Petronas Towers, Malaysia
Commerzbank, Frankfurt, Germany
Milwaukee Art Museum, Wisconsin
Swiss Re Tower (the Gherkin), London, U. K.
“The Gates” Outdoor Art Installation, Central Park, New York
Royal Ontario Museum Renaissance (Michael Lee-Chin Crystal), Toronto
Trees of Stephen Avenue, Calgary