LAX Theme Building to undergo shaking test
By Sandy Bui
May 2, 2010 9:00 p.m.
UCLA engineers will perform a shaking test of the Los Angeles International Airport Theme Building, which has been undergoing upgrades to endure possible future earthquakes, on Tuesday.
The personnel of UCLA’s Network for Earthquake Engineering Simulation program has been involved in the seismic retrofitting efforts of the building since 2007, when a chunk of the building fell off unexpectedly, said Robert Nigbor, the co-principal investigator and operation manager of the program.
Following a presentation by team members at the event, invited attendees will experience a 10-minute simulated shaking of the building, courtesy of the team’s portable eccentric mass shaker nicknamed Mighty Mouse.
Mighty Mouse, which will be mounted on the building’s roof on Tuesday, produces a violent force of up to 20,000 pounds and is remotely computer-controlled by UCLA engineers who monitor the shaking, Nigbor said.
Computers will also display the data recorded from sensors examining the shaking of the building.
The level of shaking will be equal to a small local earthquake or a large distant earthquake like the one in Baja California that L.A. residents felt weeks ago, Nigbor said.
“We’re certainly not shaking it at a level that would damage the building,” Nigbor said.
Under the direction of principal investigator John Wallace and Nigbor, UCLA’s team has performed experimental modal analysis, which involves measuring the building’s vibrations to understand the structural properties that contribute to earthquake response, Nigbor said.
The team’s 2007 measurements provided the structural engineers who designed the building’s seismic retrofit with data to create accurate computer models of the structure. Additional shaking tests have since verified that the building can indeed endure strong earthquake shaking, Nigbor said.
Even after the building’s expected grand re-opening in June, the team will continue studying the building with permanent earthquake-monitoring instrumentation as part of ongoing research within the civil engineering department at UCLA, he added.
Like the pendulum of a clock, every building vibrates at a certain frequency, said Luke Ensberg, a civil engineering graduate student who attended a structural test for the building last week.
Buildings have to be carefully designed so that the natural frequency they vibrate at is dissimilar to the natural frequency of earthquakes. If the two frequencies match, a building can fall apart, Ensberg said.
The Theme Building’s seismic retrofit involved the addition of a tuned mass damper, which is a steel weight mounted to the building that counteracts earthquake vibrations and helps preserve the landmark’s historical fabric and appearance, Nigbor said. Otherwise, conventional earthquake strengthening would have involved the addition of concrete and a modified appearance, he added.
Speaking of his experience at the building’s structural test last week, Ensberg said he was fascinated with the potential of the eccentric mass shaker.
“I understood it was exerting thousands of pounds on the frame of the structure, and I was wondering if windows were going to pop out,” Ensberg said.
“It wasn’t difficult to stay standing at all, but it doesn’t take a lot of vibration to cause serious damage to a building,” Ensberg added.
Ben Ferrero, a civil engineering graduate student who has worked with the team in recent shaking tests of the Theme Building, said seeing his studies applied in the field resonates with him the most.
“To be able to take the data that we did and put it in the computers and actually see what it physically means ““ that’s the most interesting part of this whole project,” Ferrero said.
As experts of experimental testing of buildings, bridges and dams, Nigbor said he and his team enjoy participating in projects of this magnitude.
“This is a fascinating, unique project for us to be involved in, and one that allows us to use all our skills and expertise and … to actually help a project that affects Los Angeles,” Nigbor said.
