UCLA earthquake engineers have played an integral role in ensuring that an architectural icon — the futuristic-looking Theme Building at Los Angeles International Airport — has a future in quake-prone Southern California.
UCLA engineers and their Mighty Mouse, a building shaker that can simulate the forces of an earthquake, helped analyze the Theme Building's dynamic properties and its response to quakes. Photos by Matthew Chin.
First opened in 1961, the Theme Building has welcomed millions of travelers to Los Angeles. In 1993, it was officially designated a Los Angeles historic and cultural monument.
In 2007, a heavy piece of stucco fell from one of the building’s arches. An inspection revealed that the arches’ internal steel was corroding inside, the result of moisture from cool, coastal air condensing inside the frame over many years. But other issues were discovered, and it was determined that the space-age landmark needed a comprehensive overhaul to protect it from earthquakes.
That’s when UCLA’s Network for Earthquake Engineering Simulation Laboratory, or NEES@UCLA, were brought onboard to analyze the building’s dynamic properties and its response to earthquakes.
UCLA research engineer Robert Nigbor, right, stands on the building's observation deck as Mighty Mouse begins to shake the building in a north-south direction. The shaker is located between the two orange poles.
“This is a very unusual structure, not only in its shape, but really if you look underneath the skin here, it’s built more like a ship than a building,” said Robert Nigbor, research engineer and operations manager for NEES@UCLA. “It’s not beams and columns like we’re used to with normal buildings. So it’s really hard to model.”
In October 2007, the lab brought one of its shake machines, dubbed “Mighty Mouse,” to the site. With a 10,000-pound maximum force, the shake machine, known as an eccentric mass shaker, operates like a pair of out-of-balance washing machines. It spins two heavy steel discs in opposite directions, much like two clock gears next to each other. This action sends a force in the form of a sine wave in one direction. The UCLA lab also has two larger, 100,000-pound shakers, otherwise known as “Popeye” and “Bluto.” These were not used here because they would have produced damaging levels of vibration, Nigbor said.
Lab members also placed a network of accelerometers, force sensors and strain gauges to assess the building’s structural performance during the simulated earthquake.
Following a series of stress tests to determine how the building would react to the shaking, UCLA engineers worked with Miyamoto International, a structural engineering firm in charge of the building’s retrofit, for about six months to fine-tune a computer model of the building.
To preserve the building’s unique profile, the redesign team couldn’t add external support structures or thicker concrete walls to make it more earthquake-resilient. “It’s probably the most recognizable building in California,” said L. Scott Markle, a civil engineer for Los Angeles World Airports. “We wanted the building to be safe in the event of an earthquake, but we also wanted the building to look the way it was.”
The key component of the $12.3 million retrofit is a tuned mass damper, comprised of steel plates stacked one on top of the other. It sits atop the building’s central cylinder on a system of rubber springs and hydraulic shock absorbers. The damper weighs 1.2 million pounds — the same as a fully loaded Airbus superjumbo jet — and helps counter and absorb the strong forces from an earthquake so the building itself will shake much less in a large earthquake.
The 1.2 million-pound tuned mass damper, wrapped in scaffolding and located on top of the building, absorbs and counteracts seismic forces.
Last week, the UCLA engineers returned to the building with their shake machine and sensors to verify the newly retrofitted building’s performance and to compare it to the results of the 2007 baseline tests.
At a demonstration held on May 4, the NEES@UCLA team turned on its Mighty Mouse shaker atop the building’s observation deck. Onlookers could definitely feel the entire building sway back and forth. To confirm the movement, several containers of blue-dyed water sloshed gently around as the shake machine spun.
“We got everything we wanted out of the testing, and the comparisons with the computer model are very close,” Nigbor said. It will take a few more months to completely analyze the data.
In another month or two, said Markle, the remaining scaffolding on the building’s observation deck will come down, and it will get a new coat of paint.
The UCLA team feels the building move as computers monitor a network of sensors placed around the building.
The NEES@UCLA lab is also working in Chile, monitoring how buildings in the capital city of Santiago are doing following the great earthquake in March. UCLA engineers have installed instruments in a few buildings and are scheduled to return to Santiago in a few weeks.
“Buildings in Chile are essentially designed using the same code we use in the U.S.” said civil and environmental engineering professor John Wallace, principal investigator for NEES@UCLA and a member of the Chile reconnaissance team. “So the performance and response of buildings down there are of great interest to us.”
The data collected can help improve computer models and help scientists better understand what could happen to buildings in an earthquake here in the United States, he said.
Learn more about the lab at its website.