Effect of seismic activity on MIT building to be detailed

April 2013

PROBLEM

The seismic monitoring of buildings is particularly important in high-population urban areas like Greater Boston. While Massachusetts’ seismic building codes are adapted from California’s, the geological conditions in the two states are very different. The soft soil of land reclaimed from the Charles River on which some areas of Boston and Cambridge are built could make structures here more vulnerable to damage from earthquakes of small magnitude, particularly if the frequency of the seismic activity matches the fundamental frequency of a structure or site. But baseline measurements of buildings in these cities in response to environmental conditions — which could help predict their response to a high-magnitude earthquake — are generally not available.

APPROACH

Researchers are using data collected from sensors to create a computer simulation model of MIT’s Green Building. L to R: Top of the building, the foundation pile caps on the bottom, and with exterior walls and floor slabs removed. Images / Peter Adam Trocha, MIT
Researchers are using data collected from sensors to create a computer simulation model of MIT’s Green Building. L to R: Top of the building, the foundation pile caps on the bottom, and with exterior walls and floor slabs removed. Images / Peter Adam Trocha, MIT

Professor Oral Buyukozturk, working with Professor Nafi Toksoz of MIT’s Department of Earth, Atmospheric and Planetary Sciences and Mehmet Celebi of the U.S. Geological Service, outfitted the 20-story Green Building on the MIT campus, the tallest building in Cambridge, with a seismic monitoring system. Designed by I.M. Pei and built in the early 1960s, the building stands 80 meters above ground, has a one-story basement, measures 14.6 meters on the east-west ends and 34 meters on the north-south sides, is made of reinforced concrete and has a foundation of thick concrete beams reinforced by rebar. Structural characteristics that make it a good subject include shear-resistant walls of concrete integrated into the outer walls of the windowless east-west ends to prevent in-plane movement; an open ground floor; and asymmetry created by having elevators at only one end of the building and heavy meteorological research equipment on the roof.

A building can move by deformation (shearing between floors, bending or torsion) or the entire structure can rotate or shift translationally. To detect deformation, the team deployed 36 accelerometer sensors at points where the building is most likely to move. Structures are impacted by both the magnitude of a seismic wave and its frequency. The site of the Green Building is known to have fundamental frequency of 1.5 hertz. Data provided by the sensors allows the researchers to compute the velocity of movement and the vibration frequency of the building.

FINDINGS

Using the accelerometer array, the team observed bending, shear and torsional deformations, as well as some of the building’s more unique structural behaviors. One nove