Posts tagged with "Earthquakes":
Seattle is updating building codes for new skyscrapers after a shocking study revealed that the power and nature of earthquakes in the region pose a significant threat to its tall buildings, one that is worse than experts could have imagined.
The Seattle Times recently reported on results from the M9 Project, a four-year study that aimed to estimate the effects of a magnitude 9 Cascadia earthquake, revealed that the vast, sediment-filled basin under Seattle can magnify the type of ground shaking that puts high-rises at risk of collapse by a factor of two to five, which can trigger stronger surface effects than earthquakes in nearby California.
When rattled by an earthquake, the Times explained, the region's glacial-packed soils, which can extend more than four miles underground, violently shake and convulse, trapping massive seismic waves within the basin that underlies most of the city. Intense shaking like this could last for two minutes, which is four times longer than the average quake. While shorter buildings under 10 stories can withstand the earth's back-and-forth motion, tall buildings tend to whip back and forth under those conditions until they are on the verge of collapse.
As the Times reported, as a result of these findings, Seattle and its neighbor, Bellevue, plan on revising seismic construction standards for new buildings over 240 feet, or over 20 stories tall. These standards will require high-rises to be stronger and more sturdy than their predecessors, without the additional cost.
The plan to revise building codes has also raised concerns regarding Seattle’s older high-rises, many of which were constructed between the 1960s and 1990s, prior to when the dangers of earthquakes were fully understood. Older high-rises have a greater risk of major damage and collapse due to their fracture-prone welded joints, which are supposed to secure the steel frame, as well as their poorly-reinforced concrete supports. Seattle’s renowned Rainer Tower, for example, with its golf-tee-shaped base, was built in the 1970s and undoubtedly has fracture-prone welds. According to the study, buildings like that are up to five times more likely to collapse during an intense earthquake than a modern building.In Seattle, where the seismic threat to skyscrapers is higher than in California because of the city's sedimentary basin, there have still been no attempts to research and pinpoint dangerous high-rises. While the city is taking steps forward by enhancing construction standards, retrofitting old concrete and steel high-rises may be the next necessary step. This may prove costly, but taking time to fix the underlying structure of older buildings could prevent serious levels of damage that can be catastrophic to the community.
In 1985 Mexico City suffered a devastating earthquake. Occurring in the early morning on September 19, the quake took the lives of more than 5,000 people. The earthquake's vibrations of the lakebed sediments beneath the city also destabilized its skyscrapers. Such was the devastation that one nine-story tower collapsed, its piles ripped from the ground. New building codes were implemented after the disaster and now Mexican architecture practice L. Benjamin Romano Arquitectos (LBRA), working alongside working alongside engineering firm Arup’s New York office, has produced an earthquake-resistant skyscraper designed to last 2,500 years.
Rising to 57-stories, Arup conceived pre-tensioned double-V hangers to brace the facade. According to a press release, in practice the skyscraper—named Torre Reforma (Tower Reform)—has an "inherent tendency to twist when subjected to lateral loads and wind" and "earthquake forces." While creating a signature aesthetic for the building, the hangers also provide visual reassurance of the its structural qualities.
Materiality was a key component of the design process for the tower. Arup said that the finish of the concrete was "critical"; the firm evaluated numerous design mixes. Their final choice resulted in a smooth surface, free from honeycombing or other flaws. Poured in increments of 27 inches, the finish highlights the color variations that are commonplace in similar types of pours.
In addition to its tectonics, the building's circulatory aspects were another area of focus. With a triangular floor-plan, LBRA strayed away from using the central core that's norm in skyscrapers. At Torre Reforma, the elevators and egress stairways are contained in the apex of the triangle. Long-span pyramidal floor trusses facilitate concealing the building's services. These trusses also enable dramatic column-free interiors and sweeping views of the city and the nearby Chapultepec Park.
Additionally, Torre Reforma is a pre-certified as a LEED Platinum Core and Shell project, as it makes use of various water conservation systems and a combination of automated and passive ventilation systems to moderate temperature.
"Arup has been indispensable in helping to transform my architectural vision into an efficient and buildable structure," said Benjamin Romano, Principal of LBRA, in a press release. "They have provided innovative solutions to the complex seismic issues in Mexico City and have been instrumental in helping the bidding contractors understand that Torre Reforma is not more complex than standard vertical construction; it just applies traditional construction methods, that contractors are already familiar with, in a new and different way."
Tabitha Tavolaro, Associate Principal at Arup and project manager for Torre Reforma, added, “Building tall structures in Mexico City often means working in constrained conditions. Challenges can include small or irregular sites, coordinating diverse teams, and, of course, seismic hazards. In this project, we partnered with LBRA to create robust solutions that bring value to the client as well as the community.”