Skyscrapers are perhaps the most iconic buildings in modern cities. However, vertical construction can have negative effects on local wind patterns. There are two main types of wind disruption caused by skyscrapers and they combine to cause a high wind speeds at street level.
The downdraught effect is caused when an individual building receives the wind head-on spreading it in all directions. The wind displaced downward towards the street speeds up since it is restricted to small spaces between buildings.
Another effect called channeling or funneling occurs when many tall buildings are built along both sides of a street simulating a natural canyon. This causes a combination of high wind speed, turbulence and noise.
The wind disruption caused by skyscrapers can make walking difficult for pedestrians and fast wind can also have a chilling effect during cold weather. Strong winds at street level can also send objects flying at high speed or they can knock down signs and other objects with a large frontal area.
The wind disruption caused by buildings provides an excellent example of why on-site weather & wind monitoring is important to provide safety.
The 20 Fenchurch Street Building nicknamed the Walkie Talkie due to its shape is a colossal 37-storey tower with 660,000 sq.ft. of office space, 23,000 sq.ft. of retail space and a rooftop garden. The building is notorious for the windy microclimate around its base which can be attributed to the severe downdraught effect caused by its shape.
In some cases, wind disruption around the Walkie Talkie has become so strong that workers have fallen over, food trolleys have been overturned and signs have been detached from other buildings. In addition, the building often causes a loud whistling sound and it had to be equipped with sunshades to mitigate glare from reflected sunlight. Apparently, the glare was so strong that it caused localised heating capable of damaging parked vehicles.
New York City is also characterised by its skyscrapers, but their downdraught effect is minimised thanks to the wide streets and avenues in the city. London, on the other hand still has many narrow streets that date from the medieval era which result in a more severe downdraught effect around tall buildings.
The 32-storey Bridgewater Place, the tallest building in Leeds also has a notable downdraught effect. Since the building was built in 2007, strong winds around its base has caused many accidents where people have been injured.
HOW TO MITIGATE WIND DISRUPTION AROUND SKYSCRAPERS
According to the City of London Corporation there have been many cases where wind studies for high-rise construction underestimate wind conditions on the street after the project is completed. So, more accurate tools and data are needed to plan for the wind effect of tall buildings.
According to field evidence, the downdraught effect is worse when a building has sharp corners and is mitigated when a structure has smooth shapes. The Gherkin is a building that provides an example of this: although it is 41 storeys tall, its rounded shape results in minimal wind disruption compared with the Walkie Talkie.
Weather monitoring systems can be deployed to study wind conditions in the streets around tall buildings and the gathered data can be used as reference when designing future projects or during its construction. As well as gathering valuable data to be used for suitable planning and risk assessment, a ‘live’ monitoring solution can provide automatic warnings when wind conditions on the street are harsh, allowing the suspension of sensitive activities such as construction work immediately.