San Francisco’s One Rincon Hill, the tallest residential structure on the West Coast, has achieved another milestone by installing the largest number of seismic sensors of any high-rise building in California, the California Geological Survey and U.S. Geological Survey jointly announced today.
Through the combined efforts of the USGS, the state survey and the building’s structural engineers, Magnusson Klemencic Associates, the building was outfitted with 72 sensors connected by more than two miles of cable to collect data on the building’s movements.
This is the first time that the USGS and a state geological survey have collaborated on an instrumentation project, according to the state survey.
California State Geologist John Parrish said the data collected provides a window into the building’s structural performance, which can in turn help structural engineers to develop safer buildings that are subjected to earthquakes.
Earthquake records from buildings can enable engineers to calibrate and confirm mathematical models used to estimate deformations the building experiences, which can also provide information about structural damage.
Ron Klemencic, the towering 6-foot 6-inch structural engineer behind the 590-foot tall One Rincon Hill tower, said his firm advised the two surveys about where to locate the sensors in order to capture the most valuable information about the building’s movements.
To handle the magnitude 6.7 or greater earthquake that scientists predict has a 63 percent probability of occurring in the next 30 years in the Bay Area, the tall, slender building was designed with an “outrigger” system that redistributes the seismic loads away from the rest of the structural system and along braces that absorb energy during an earthquake.
Klemencic said the building is the only residential high-rise in San Francisco with an outrigger system. Another of the building’s unique structural features are the four water tanks located on the building’s roof that reduce sway associated with wind and seismic loads.
Because of the building’s specific structural system and height and the density of the instrumentation array, Parrish said scientists expect to collect “unprecedented data from this building.”
The sensors are clustered in groups of three across 19 of the building’s stories, allowing scientists and engineers to determine the displacements and rotation of each floor, said Anthony Shakal, of the state survey.
The devices produce a digital record that allow for calculation of the acceleration, velocity, displacement and frequency of ground motions for individual displacement directions.
Six sensors were installed at the building’s base, where scientists are also interested in information about how the structure rocks on its foundations, Shakal said.
While the sensors are continuously monitoring the building’s movements, the enormous amount of data is not automatically captured. Instead, Shakal said, academics may request capture of ambient data, which will then be stored and disseminated through the Center for Engineering Strong Motion Data.
The center is operated by the California Department of Conservation’s Strong Motion Instrumentation Program in partnership with the USGS National Strong Motion Program.
Otherwise, the system will automatically save data following seismic events with magnitude greater than or equal to 3.0, as this strong shaking data is most useful to verifying mathematical models.
These academic advancements are critical to designing safer buildings by providing insight into how damage from strong shaking occurs and by improving earthquake provisions in building codes.
When subjected to dynamic loads such as earthquakes, buildings respond in ways that are dependent on their individual characteristics–size, geometry, structural system, foundation type, and construction materials.
In the case of One Rincon Hill, the building experiences high stresses in its upper stories, which were in turn outfitted with a greater proportion of the sensor clusters, Klemencic said.
From vision to completion, the instrumentation installation took about five years.
“It took us a while to get all of the pieces together,” Shakal said, noting that the effort required coordination between the state and local government agencies, as well as other vested parties.
One of the biggest hurdles to routinely outfitting buildings with seismic instrumentation is the cost associated with the devices, Shakal said.
Although sensor technology has advanced to allow some sensors to transmit information wirelessly, removing the need for the long length of connective cables, Shakal said the structural steel present in buildings significantly interferes with wireless signals.
Shakal said the state survey hopes to instrument more high-rises and hospitals in the future.
“It’s important to see how a wide variety of buildings react to seismic shaking,” Shakal said.
With construction set to begin in the near future on the second residential tower at the Rincon Hill complex, a 541-foot tall 52-story building with about 300 units, Klemencic said his firm hopes to also instrument that building.
“This is a tremendous opportunity for the industry as a whole,” Klemencic said of the landmark instrumentation effort.
Patricia Decker, Bay City News