Shake, Rattle and Bend : Redesigned Structure Sustains Minimal Damage in Big Quake, Simulation Shows

After simulating the most powerful earthquake California is ever expected to face, UC San Diego researchers say that it is possible to build buildings that can withstand the Big One with minimal damage.

Scientists at the Charles Lee Powell Structural Systems Laboratory announced Thursday the results of the first full-scale test for earthquake resistance on a specially designed five-story building.

Hairline cracks spread through the building. Floors suffered fan-patterned fracturing around doorways. Doorsills and jambs crumbled. Almost all of this was according to plan, said M.J. Nigel Priestley, one of three principal investigators for the project.

Like the parable of the flexible reed that survived a flood while the rigid oak tree was swept away, the test building was designed to bend and torque with a quake’s undulations, Priestley said. The concept was to produce a building that could “deform without losing strength,” Priestly said.

“Through a design that allows for ‘controlled damage,’ we avoided the one large crack that typically results in a building collapsing,” Priestly said. “We planned for many small cracks that would be well distributed.”

The most significant design innovations were simple ones, said Frieder Seible, associate director of the Powell Laboratory. Reinforced steel bars in the building’s walls were repositioned to allow for flexibility. Doors and sills had larger gaps to cushion the impact from sliding or twisting walls. Pliant building materials were used to fill the gaps.

Results of the experiment are expected to be published by the beginning of next year and will be used to reform building codes across the nation for small to mid-range high-rises built of masonry materials, said Gilbert A. Hegemier, director of the Powell Laboratory.

Experiments were based on a 25-second simulated temblor at the laboratory, where a reinforced masonry building was rattled by more than 2 million pounds of computer programmed-hydraulic pressure.

The quake simulation was produced by 10 hydraulic jacks--two connected to each floor of the five-story building. The shaking was slower than a real quake in order to measure and analyze its effects.

The quake was broken into different levels of intensity, and pieced together during 75 tests spread over August and September, Kingsley said. The end result was equivalent to putting the building through 25 seconds of an earthquake more intense than any expected in the state.

Kingsley said the scale used to measure real earthquakes cannot be applied to the one simulated by the laboratory because the scale only measures the strength of the quake, and does not take into account environmental factors that can damage buildings. However, he said, the laboratory quake was judged to be more intense than the 1989 Loma Prieta earthquake in the Bay Area and the 1987 Whittier earthquake in Los Angeles County.

The $3-million Powell Laboratory, built in 1986, is the first in the nation to house a quake experiment on a full-sized building. The project cost $600,000 and was funded by the National Science Foundation and masonry trade groups.

Researchers on the seven-member team are beginning to develop methods to repair damage suffered by the test building.