What happens when you put a fully equipped five-story building — which includes an intensive care unit, a surgery suite, piping and air conditioning, fire barriers, and even a working elevator — through a series of high-intensity earthquakes?
Structural engineers at the University of California, San Diego conducted a two-week series of tests on the world’s largest outdoor shake table. The goal of the project was to ascertain what needs to be done to make sure that high-value buildings, such as hospitals and data centers, remain operational after going through an earthquake. Researchers also will assess whether the building’s fire barriers have been affected by the shakes.
Throughout the two weeks of testing, engineers monitored the building’s performance with more than 500 high-fidelity sensors and more than 70 cameras that recorded the movement of key elements and components inside the building.
This was the first time in the United States that tests focused on a broad range of nonstructural systems and equipment that can malfunction during an earthquake, such as a working elevator, stairs, and a broad array of medical equipment. The tests also included modern ceiling systems, a heating and air conditioning system, functional sprinklers, computer servers, large and small laboratory equipment, and electrical equipment and wiring. The 80-foot-tall structure also was equipped with a large water tower and an air conditioning and heating unit on its roof. The exterior of the building was complete with heavy precast concrete cladding, as well as synthetic stucco, each commonly used in commercial construction.
This was also the first time that a base isolation system was tested under a full-scale building on a shake table in the United States. The system was comprised of large cylindrical rubber bearings that isolated the five-story building from most of the lateral motion it would normally experience during a temblor. During the second week of testing, the base isolation bearings were removed and the building’s foundation was anchored directly on the shake table.
This was the first time that a building was subjected to fire testing after being put through a series of simulated seismic events. Researchers from UC San Diego and the department of fire protection engineering at the Worchester Polytechnic Institute studied the performance of active and passive fire protection systems, which will provide insight into damage caused by earthquakes. This month, engineers will conduct fire tests in the building, tracking temperatures and the movement of smoke to help gauge the potential for fire spread in an earthquake-damaged building.
Researchers also hope to better understand what needs to be done to make sure medical centers remain operational after a temblor. The building’s top two floors were outfitted with a surgery suite and intensive care unit, two components of the project supported by the California Seismic Safety Commission, which investigates earthquakes and recommends to the governor and state legislature policies that will reduce earthquake risks. Likewise, the fire-related data will help engineers model the fire performance of buildings damaged in earthquakes.
Sensors were placed strategically throughout the building to measure how components perform. For example, 230 accelerometers measured how fast the building and its nonstructural components moved during the simulated temblors. In addition, 160 sensors, including high-resolution GPS devices, measured the relative displacement between two points, while 50 strain gauges measured the deformation of the rebar buried in the building’s concrete foundations. About 80 cameras were focused on the building, with most of these distributed within the interior of the building to monitor the nonstructural elements during the tests.
During the two weeks of testing, researchers put the buildings through a variety of simulated temblors, using motions that have been recorded from the 1994 6.7-magnitude Northridge earthquake, the 2002 7.9-magnitude earthquake that took place in Denali, AL, the 2010 8.8-magnitude earthquake in Chile, and the 2007 8.0-magnitude earthquake in Peru.
During this complex series, researchers also investigated the performance of nonstructural systems, which provide evacuation support for the occupants of a building. Scientists hope the tests will help find ways to keep elevators and stairs safe and functional after a major temblor.