From "height" to "height limit" skyscraper heat should cool down
Recently, the Suzhou South Central Center, which has received much attention, has started construction. More than a month ago, in the post-approval announcement issued by the Planning and Construction Committee of Suzhou Industrial Park, it can be seen that the construction height of the Central South Center has dropped from 729 meters to 499.15 meters. The self-reduction height of the Central South Center can be found in the "Notice on Further Strengthening the Management of Urban and Architectural Features" (hereinafter referred to as the "Notice") issued by the Ministry of Housing and Urban-Rural Development and the National Development and Reform Commission on April 27. The "Notice" stipulates that blind planning and construction of super high-rise "skyscrapers" in various places should be strictly restricted. Generally, new buildings over 500 meters are not allowed to be built. Buildings over 250 meters are strictly restricted. Buildings over 100 meters should be fully demonstrated...
Before the release of the "Notice", this "lowering" wind was not uncommon: the Xi'an China International Silk Road Center building was reduced from 501 meters to 498 meters, and the height of the super tower of the main building of the super high-rise project in Chengdu Tianfu New District was changed from 677 meters. 489 meters...
When did mankind begin to "adore" skyscrapers, and what caused skyscrapers to move from "pulling up" to "limiting height"?
26 buildings over 300 meters were built globally last year
"The dangerous building is a hundred feet tall, and you can pick up the stars. You dare not speak loudly and fear the heavens." The Tang Dynasty poet Li Bai did not think of the hundred-foot tall building in his poem more than 1,000 years later when he wrote this "Yesu Mountain Temple" Compared with today's skyscrapers, it is already a rare thing.
There is no strict definition of the height of skyscrapers. In my country, the conventional definition is that skyscrapers with a building height of more than 200 meters.
The reporter checked the website of the skyscraper center of the World Tall Building and Urban Habitat Society. In 2019, 26 super high-rise buildings over 300 meters were built in the world, far exceeding 18 in 2018. Another data shows that in 2018, among the top 10 cities with the largest number of completed skyscrapers in the world, China has 6 cities on the list, 3 of which are located in the Midwest.
Skyscrapers have appeared since the late 19th century. "With the development of the city, the Chicago School has set off the first wave of high-rise buildings in the world." Zhou Qi, a professor at the School of Architecture of Southeast University, told Sci-Tech Daily that in 1871, a fire in Chicago, the United States, destroyed the city and caused a disaster. Later, the architects boldly used steel structures to build super high-rise buildings. Chicago's famous "Home Insurance Building" was once regarded as the world's first skyscraper.
In the 1930s, New York replaced Chicago as the center of high-rise buildings in the world. The Empire State Building, completed in 1931, drove the rise of a group of over 200-meter super high-rise buildings in Manhattan at a height of 381 meters. In the 1970s and 1980s, high-rise buildings began to become popular all over the world, and the Middle East, Southeast Asia and other regions joined the skyscraper "club".
"As land becomes more expensive, super high-rise buildings can improve land use efficiency, increase the use area at vertical heights, and at the same time be a symbol of capital and strength. These new city landmarks also bring invisible advertising effects for capital." Zhou Qi said.
Looking around the country, super high-rise buildings are constantly refreshing the new heights of the skylines everywhere. The 632-meter Shanghai Center Tower in Shanghai is currently the tallest building in China; the 592.5-meter Ping An Financial Center in Shenzhen; the 528-meter "China Zun" Beijing CITIC Tower in Beijing; the Guangzhou Tower with a 454-meter main body and the 450-meter-high Nanjing The Zifeng Building has become one of the city’s business cards.
High building maintenance costs and potential safety hazards
Super high-rise buildings once led the fashion industry in the world, but their super high construction and maintenance costs, potential safety hazards, low economic returns, and the impact on the ecological environment have gradually emerged.
"The higher the skyscraper is covered, the greater the wind load, the greater the amount of steel used, and the higher the cost of the structure." Zhou Qi said that according to the construction cost in recent years, the construction cost of a super high-rise building of 100-200 meters is about per square meter. The construction cost of skyscrapers over 200 meters is about 10,000 yuan per square meter, which is high.
After the skyscraper is built, it still needs to face higher maintenance costs. Zhou Qi introduced: "The elevator of the skyscraper must run faster, the faster the speed, the greater the technical difficulty of the elevator, so the higher the maintenance cost; the spray system Maintenance will increase with the increase of floors; some skyscrapers abroad have two workers hired to clean the facade of the building. The higher the building, the greater the wind load and the higher the cost of manual cleaning. ."
Li Yujia, the chief researcher of the Guangdong Housing Policy Research Center, also pointed out that the cost of elevators, insulation, lighting, cleaning, and properties in skyscrapers is about twice that of ordinary residences.
Building skyscrapers is not just about spending more money, it can sometimes put people at risk.
In the movie "Skyscraper Rescue", the 96th floor of a 200-story skyscraper caught fire, and the fire protection system above 96 floors was attacked by hackers and could not be activated, causing the building to instantly become a sea of fire.
"At present, the height of fire ladders in China is generally 50 meters, and individual fire trucks can reach 100 meters. This means that in the event of a fire in a high-rise building above 100 meters, the building's own fire protection system basically needs to be rescued, which is more Passive." Lv Weiya, a professor at the School of Urban Construction, Nanjing University of Technology, told Sci-Tech Daily.
Although public sprinkler systems in some high-rise buildings will be equipped with automatic sprinkler systems, the temperature rises during a fire, and the sprinklers of the automatic sprinkler systems will automatically sprinkle water to extinguish the fire. At the same time, the fire pump will be activated for 1 hour, but the sprinkler system The effluent intensity is not large, so it can only be used to suppress the initial fire.
Super high buildings are also not conducive to energy saving. Because the high-rise winds are strong, the windows of super high-rises are often closed, relying only on the air conditioning and fresh air system in the building for ventilation. From an energy perspective, this is a huge consumption. In the view of Wang Yongping, a professor at the School of Architecture, Nanjing University of Technology: "The skyscrapers are crowded, and the ventilation is not very good. In the case of infectious diseases like new coronary pneumonia, the safety risks are also higher."
In addition, Zhou Qi pointed out that skyscrapers will bring some transportation and ecological problems. For example, a 500-meter skyscraper can often accommodate tens of thousands of people to work. In the morning and evening rush hours, traffic and people will cause traffic jams. Another example is light pollution, the seemingly lightweight glass curtain wall, will reflect sunlight to many nearby buildings. At the bottom of the skyscraper group, there will also be a wind tunnel effect, forming a great wind current.
Construction needs comprehensive consideration and can not blindly pursue height
After more than a century of development, the construction technology of skyscrapers has been quite mature, but many experts said that the living experience of modern people should more advocate energy saving, environmental protection, and return to nature.
In the "Several Opinions on Further Strengthening the Management of Urban Planning and Construction" issued by the Central Committee of the Communist Party of China and the State Council, for the architectural design management, it proposes an "economic, green and beautiful" architectural policy, highlighting the functions of the building as well as energy saving, water saving, Land saving, material saving and environmental protection prevent the one-sided pursuit of the requirements of building appearance and image.
"Building the city's skyline requires comprehensive consideration of the city's economic development, location, and aesthetics." Zhou Qi said that in terms of comprehensive land use efficiency, economic benefits, and housing availability, a height of about 100 meters is suitable for living Office and office buildings are also the most economical heights for high-rise buildings; between 100-200 meters is a reasonable height range; wind loads on skyscrapers over 200 meters will greatly increase, fire protection levels will also increase, and room availability will also drop significantly.
He believes that in economically developed and densely populated first-tier and second-tier cities, you can consider building super-tall buildings within 200 meters. But for third- and fourth-tier cities, economic activity is not so active, and the population is not large enough, so construction needs to be cautious.