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The growing number of extraordinarily tall, or “supertall,” buildings that have shot up around the globe can present significant risk management concerns in construction and maintenance.
Concerns can include seismic and natural catastrophe activity, dangers posed by wind loads and fire, the choice of building materials, threats posed by cranes, congestion surrounding a building site, the environmental impact and worker safety.
These issues aren’t unique to supertall buildings, but they are exacerbated in their complexity the higher the buildings are constructed and call for sophisticated risk management techniques, experts say (see related story).
While there is no official standard for what is considered a supertall building, the Chicago-based Council on Tall Buildings and Urban Habitat considers a “supertall’’ building to be at least 300 meters (984 feet) tall and a “megatall” building to be at least 600 meters (1,968 feet). A total of 173 supertalls and three megatalls have been completed globally, according to the organization.
As a building gets taller, it is “going to have more risks and exposures associated with it, both from a risk management standpoint and from a building standpoint, with respect to the contractors and the actions they need to take,” said Erik Davis, Los Angeles-based managing director, construction practice, for R-T Specialty LLC. The risks include the long-term nature of the building “and how well it’s going to perform over time,” he said.
Fire is a particular hazard, observers say. Just as in building a bonfire, with the materials stacked rather than laid flat, by stacking combustibles one atop the other “you’re now creating the condition where a really large fire can spread floor to floor,” said Katherine Klosowski, global vice president of natural hazards and structures engineering at FM Global in Johnston, Rhode Island. The structures’ height makes it harder for firefighters to extinguish blazes, though fire protection systems can address this issue, she said.
Wind risk is a concern facing construction firms, said John Peronto, senior principal with engineering firm Thornton Tomasetti in Chicago, who has worked on the Jeddah Tower in Saudi Arabia, which upon completion — now delayed because of the pandemic — would be the world’s tallest building at 3,280 feet. “Just because they’re tall, they move a larger amount,” he said.
“There are different tolerances when you build something that tall,” particularly related to nonstructural issues such as components used to finish the building, some of which could be perceived as brittle, said Mr. Peronto, who chaired an American Society of Civil Engineers committee that published a manual on the design and performance of tall buildings that proposed standards to be followed.
Windshear and ice buildup are major exterior issues, and the use of a greater percentage of glass cladding to cover the exterior, rather than masonry concrete, can pose water risks, said Tom Grandmaison, Aon PLC’s Boston-based chief broking officer for its construction practice.
Rob McDonough, New York-based U.S. construction leader for Marsh LLC, said, “We are seeing more focus on resilient materials and more preconstruction engineering to make sure buildings can adapt for different weather events” as well as for ground disturbances such as earthquakes, he said.
A building site’s geographic suitability is also a consideration. “We’ve seen several projects” where it was not suitable to construct at a particular location, Mr. Davis said.
Many experts point to San Francisco’s Millennium Tower, a 645-foot-tall residential building whose foundation sank 18 inches, in part, tilting the building and requiring a $100 million fix, according to news reports. Ensuing litigation led to a settlement of about $500 million in 2019.
Environmental impact is another consideration. Studies have shown these buildings can deter the wind’s ability to disperse pollution, Mr. Davis said.
“Most of these buildings are in urban environments, where there’s a significant amount of building density around’’ the construction site, which “highly dictates how you’re able to use and prepare the site,” said Brandon Perry, architects and engineers large firms program manager for Victor Inc., based in Bethesda, Maryland.
Sunlight is another issue. Brian Cooper, senior managing director, U.S. construction, at Arthur J. Gallagher & Co., said most high-rise buildings are clad with reflective glass and their placement, size, shape and adjacent facilities must be considered. Drivers on a nearby highway, for instance, could be dangerously blinded by a reflection.
The most obvious risk to workers at supertall construction sites is falling. Some companies use “cocoon” systems at construction sites, which keep workers from falling farther than five feet, Mr. Grandmaison said. These are safety enclosures that are raised higher as the construction proceeds, protecting both workers and pedestrians.
In addition, “to protect workers, you want to create an environment” where they enter and leave the building as infrequently as possible, Mr. Cooper said. In some high-risk construction projects, this has been addressed by using large cargo ship containers to house facilities such as nursing stations and even restaurants, he said. The containers are hoisted to higher floors as construction proceeds.
Another recent innovation is incorporating hooks on the structure’s steel beams, so workers can easily connect their fall protection devices, and wearables, which can warn workers during the pandemic if someone is too close, Mr. Cooper said.
Observers say one unknown factor regarding the future of supertall buildings is whether demand will be permanently diminished by the pandemic-induced increase in telecommuting.
Many observers believe, however, that while there may be a short-term effect, the appeal of cities will eventually be revived. People will say, “I’m sick of looking out my window. I want to be back in the city,” Mr. Cooper said.
Good planning, coordination and adopting up-to-date techniques are essential elements in supertall buildings’ risk management, experts say.