The Brihanmumbai Municipal Corporation (BMC) has made it mandatory for wind tunnel tests to be conducted on high-rise buildings in Mumbai that are more than 150 metres (above 45-50 floors) tall.
The Mumbai civic body’s Technical Committee for High-Rise Buildings said the decision was taken to ensure the structural safety of tall buildings.
"We have made it mandatory for conducting wind tunnel testing whenever a new proposal is submitted for buildings taller than 150 meters,” said Shashank Mehendale, a structural engineer who is a member of the committee.
“It is not some add-on as it is already there in the tall buildings code of 2017, but we have just made it mandatory in the high rise-committee’s Standard Operating Procedure. The idea was to have a uniform or common SOP for all tall building proposals rather than deciding case-to-case."
A global practice
Wind tunnel testing is used in the design of tall buildings globally to identify wind-induced structural loads and responses for which the superstructure must be built.
According to the US-based Council on Tall Buildings and Urban Habitat (CTBUH), wind tunnel testing has become a commonly used tool in the design of tall buildings since the 1960s.
It was pioneered, in large part, during the design of the World Trade Centre towers in New York.
The BMC’s high-rise committee said the decision to make wind tunnel testing mandatory was taken in the backdrop of an increase in high-wind episodes in Mumbai.
"Wind tunnel testing will help one to understand how the wind pressure, forces and pattern will be generated on the structural elements including the beam and columns of a building,” said Mehendale, who is also chairman of the structural sub-committee of the Practising Engineers Architects and Town Planners Association (PEATA).
“There are certain wind forces prescribed by the Indian Standard Code that have to be maintained for a particular design, and the wind tunnel testing will help us arrive at more realistic (estimates of) wind forces and (ensure) safer high-rise buildings," he said.
Indian Standard Code
The codes state that wind effects on buildings with a height more than 150 meters shall be determined by a wind tunnel study. According to housing.com, Mumbai has more than 4,000 tall buildings.
The code in this context reads: "For buildings, (a) with height greater than 150 m, or (b) with complexities in plan or elevation geometry, or (c) sited on complex topography with group effector interference effect (existing and future potential), or(d) whose natural period is greater than 5s, wind effects shall be determined by site-specific wind tunnel studies."
The world's tallest building, the 828-meter-high Burj Khalifa in Dubai, also underwent wind tunnel testing.
Wind tunnel tests were also conducted on several buildings in Mumbai that are 200 metres high, with their developers voluntarily performing the tests because they are part of the Indian Standard Code.
"As buildings go higher, the speed of air hitting them rises and impacts occupants by overly frequent perceptible building motion, increasing ground winds below and aerodynamic interference in neighbourhood buildings,” said Bijal Panchmatia, design director at The Moneta Design.
“For a design team, wind tunnel testing will be of value which can help in wind-induced structural loads and cladding pressure for façade design."
"In designing Burj Khalifa, extensive wind engineering demonstrated the impact of the design concept's dynamic response against wind forces, an excellent example of a stable skyscraper with a successful collaboration of wind engineering, architectural aesthetics and structural engineering," Panchmatia added.
Climate-change effect
According to weather experts, because of climate change, episodes of high wind speed for a shorter span have increased globally, not just in Mumbai.
Mahesh Palawat, vice president of meteorology and climate change at Skymet Weather, said: "This is a good decision taken in Mumbai considering testing of wind should be there for design mitigation.”
Palawat added: "Due to climate change, intensity and frequency of extreme weather conditions episodes have increased. For example, a decade ago, the wind speed during extreme weather conditions like thunderstorms or thunder showers used to be around 50-60kmph for a shorter span, which has now gone up to 70-80kmph. Along with this, instances of rare episodes of wind speed going up to 100kmph for a very short span have also increased."
Wind tunnel tests provide more accurate design information that takes into account a building’s specific architecture and its surroundings, said Boman Irani, president of Confederation of Real Estate Developers' Association of India (CREDAI)- Maharashtra Chamber of Housing Industry (MCHI).
“This allows the architects and structural designers to maximize design efficiency while ensuring reliability targets are met. Wind tunnel testing is helpful to check the behaviour of taller structures or those of unusual shape and form to withstand the wind velocity and design them to perform stably during calamities including hurricanes and storms,” Irani added.
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