Oct. 23, 2012 The two-story building on West Commercial Avenue in El Centro, CA was built in the 1920s and has withstood four major earthquakes in 1940, 1979, 1987, and 2010 but it may not be standing for long.
That's because a research team that includes Babak Moaveni, assistant professor of civil and environmental engineering at Tufts University School of Engineering, plans to shake and rumble the structure until it's on the verge of collapsing into a heap of debris and dust.
Moaveni is collaborating with Andreas Stavridis, assistant professor of civil engineering at the University of Texas-Arlington, on a National Science Foundation-funded study to assess how buildings made with reinforced concrete frames and masonry infill walls hold up during an earthquake. The data will also be used to refine existing analytical models and techniques that engineers use when evaluating seismic safety of similarly constructed buildings. The research team also includes engineers from the University of California, at Los Angeles (UCLA).
Thousands of such buildings exist in earthquake-prone places like Los Angeles, San Francisco, the Mediterranean and Latin America, and they are vulnerable to serious damage. "These buildings were built and designed years ago according to building codes that have since become outdated," says Moaveni.
Using an "Eccentric-Mass" Shaker to Rattle a Building
Typically, after an earthquake, owners of a building like the one on West Commercial Avenue would have the structure repaired and maybe retrofitted so that it could endure the next quake. But damage from the 2010 earthquake was so severe that repair was not worth the cost. Owners and the city officials decided to have it demolished.
That's when Moaveni and Stavridis came forward. In the first phase of the project, the engineers will record the building's existing condition. Then, the team will install a spinning device called an eccentric-mass shaker on the building's roof. This device will induce further damage by simulating the pulsing and vibration of an earthquake rattling the structure from the top down. This has not been done before with an entire structure with that degree of damage. "We are glad that the building owners realized that the building's misfortune has presented a unique research opportunity for us," Stavridis explains.
The researchers will install cameras at critical locations of the structures to observe damage as the test progresses. At specific intervals, they will also halt the shaker to assess and document structural damage, through visual inspection. Computers will also record data from sensors inside the building. With the initial measurements as a baseline, the researchers will evaluate and quantify progressive damage sustained by the building as it is shaken apart.
Field testing of full-scale structures using mechanical shakers plays an important role in this type of seismic research. In previous experiments, researchers have experimented on wall portions or sections of buildings using low-to-moderate levels of vibrations. "This is a very challenging project but a great research opportunity because we are working with an entire existing building," says Moaveni.
In their project, Moaveni and Stavridis plan to exert large-amplitude forces on the building. "We don't know if we will shake the building until it collapses," Moaveni says. "But, at a minimum, we will shake it until it is on the verge of collapse."
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