Earthquakes, explosions and even day-to-day vibrations can cause structural damage to a building that may go unnoticed until it starts to cause dangerous problems. New research, however, is allowing technology enriched smart buildings to sense this type of internal damage so it can be fixed before issues arise.
Over the past few years, scientists at the Massachusetts Institute of Technology (MIT) are developing smart buildings that can sense ambient vibrations and monitor itself for internal signs of damage or mechanical stress in real time. Tracking the “health” of buildings is becoming more important than ever, as our maturing building stock begins to show dangerous signs of ageing.
“The broader implication is, after an event like an earthquake, we would see immediately the changes of these features, and if and where there is damage in the system,” says Oral Buyukozturk, a professor in MIT’s Department of Civil and Environmental Engineering (CEE).
“This provides continuous monitoring and a database that would be like a health book for the building, as a function of time, much like a person’s changing blood pressure with age.”
The MIT based team included lead author Hao Sun and earth, atmospheric and planetary scientists, Aurélien Mordret, Germán Prieto and M. Nafi Toksöz. They tested their computational model on a 21-story building, the tallest structure in Cambridge, Massachusetts, which was erected in the 1960s using reinforced concrete.
(Left to right): M. Nafi Toksöz, professor in the Department of Earth, Atmospheric and Planetary Sciences (EAPS); Oral Buyukozturk, professor in the Department of Civil and Environmental Engineering (CEE); and Hao Sun, a postdoc in CEE. The Green Building, behind them, has 36 accelerometers that record vibrations and movements on selected floors, from the building’s foundation to its roof. Credits Photo: Jose-Luis Olivares/MIT
Back in 2010, Toksöz and colleagues teamed up with the United States Geological Survey (USGS) to outfit the Green Building with 36 accelerometers that record vibrations and movements on selected floors, from the building’s foundation to its roof.
“These sensors represent an embedded nervous system,” Buyukozturk said. “The challenge is to extract vital signs from the sensors’ data and link them to health characteristics of a building, which has been a challenge in the engineering community.”
To meet this challenge the researchers created a finite element model — a numerical computer simulation that represents a large physical structure, and all its underlying physics, as a collection of smaller, simpler subdivisions. They then plugged various parameters, including strength and density of concrete walls, slabs, beams, and stairs in each floor, into the high-fidelity finite element model.
The idea behind the system was that the researchers could introduce an excitation to the simulation, such as a vibration, and the model should be able to predict how the building and its various elements should respond.
“But the model uses a lot of assumptions about the building’s material, its geometry, the thickness of its elements, et cetera, which may not correspond exactly to the structure,” Buyukozturk said. “So we are updating the model with actual measurements to be able to give better information about what may have happened to the building.”
In an effort to better predict the effects of vibrations on buildings the group mined data from the building’s accelerometers. They were searching for key characteristics that correspond directly to a building’s stiffness, flexibility or other indicators of “health”. In doing so, the team created an entirely new form of seismic interferometry that reveals how a vibration’s pattern changes as it travels through a building, from the ground to the roof.
“We look at the foundation level and see what motions a truck, for instance, caused there, and then how that vibration travels upward and horizontally, in speed and direction,” Buyukozturk said.
The new model was put into action during a two week period in May 2015 and showed that the 50 year old building is safe but is subject to significant amounts of vibration on its upper floors. “The building, which is built on soft soil, is long in one direction and narrow in the other with stiff concrete walls on each end. Therefore, it manifests torsional movements and rocking, especially on windy days,” Buyukozturk said.
The research team hope the study, which was published in the journal Mechanical Systems and Signal Processing, will lead to a new generation of smart buildings that can sense internal damage in real-time. Such sensory intelligence will save on costs through predictive maintenance, while making our buildings and cities safer for all citizens.
“I would envision that, in the future, such a monitoring system will be instrumented on all our buildings, city-wide,” says lead author Hao Sun. “Outfitted with sensors and central processing algorithms, those buildings will become intelligent, and will feel their own health in real time and possibly be resilient to extreme events.”
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