Sometime next year, the slow, deliberate destruction of a reinforced concrete masonry building will begin at the University of California, San Diego, in the first earthquake research test of its kind in the United States.
The results could bring improvements in design and construction methods for many buildings, especially in the West, and thereby reduce substantially the casualties and property damage from a major quake. A large temblor might kill more than 20,000 people in Southern California, according to federal government predictions.
The key element in the new testing lab under construction at the university is an 18-foot-thick, 50-foot-high concrete wall known as a strong-back or reaction wall. Scientists will be able to construct a full-scale building up to five stories tall and 50 feet wide next to the wall and, by positioning hydraulic rams between the wall and building, create earthquake-type forces.
Until now, the only reaction walls to test full-size buildings have been built at a national science center in Japan, where a joint U.S.-Japan earthquake research program already has tested full-scale buildings of steel and reinforced concrete.
"This will be the first lab in the U.S. where we will be able to verify computer simulations developed to determine whether a building is designed adequately for earthquakes," said Gilbert A. Hegemier, an engineering professor who has spearheaded efforts to build the facility. The lab is being funded jointly by UCSD and the National Science Foundation and will be available to researchers nationwide.
"No one knows for certain that the (computer) simulations are accurate," Hegemier said.
He and Frieder Seible, an assistant professor working on the project, stressed that the lack of confirming data does not mean all present buildings are unsafe.
"We're not saying that the tests will show designs are wrong, but rather that there are probably ways to make buildings safer," Seible said.
Earthquake research on building design in the United States has traditionally been carried out by testing individual components of a structure, such as the walls or floors, or the intersection of a beam and a column. In addition, scale models of buildings--from one-third to one-fifth actual size--are subjected to earthquake-type movements by placement on computer-controlled shaking tables. The largest one, at UC Berkeley, measures 20 feet by 20 feet.
"A shake table comes closest to actually simulating an earthquake," Hegemier said. "But because you have to use a scale model, there can be difficulties." Although steel can be scaled down with good accuracy, there is much more of a problem with brittle materials, such as concrete or brick, he said. Concrete consists of sand and gravel bonded together with cement, and there is difficulty in accurately making so-called "microconcrete," using rocks and sand to scale.
Effects of Combinations
Also, researchers are not certain that materials and components, when tested separately and then combined for performance only through mathematical models, behave as predicted when subjected as a single mass to an earthquake.
A strong-wall facility of the kind UCSD is building is much less expensive than a full-scale shaking table would be. The facility will cost about $2 million to construct and several million more to equip. By comparison, a shaking table large enough to accommodate a full-scale five-story building would cost upwards of $200 million, John B. Scalzi, an engineer with the National Science Foundation, said.
The earthquake lab will resemble a large movie theater from the outside, with 120-foot-long sides and a 64-foot clearance from floor to ceiling. Inside, the floor itself will be raised eight feet from the foundation, so that fork lifts can be driven under it to position hydraulic rams for testing.
The strong wall will be at one end of the building, in essence functioning as a floor raised perpendicularly. Rams will be connected from the wall to a full-scale building.
One-Year Test Period
The testing of the first building will take place over a year's time. The hydraulic rams will be programmed to exert certain forces based on data developed from previous component testing and from actual earthquakes.
Depending on how the building reacts to the strain, subsequent simulations will be revised. Cracks or damage to the structure may be repaired and reinforced, and tested again to see if improvements will better withstand earthquake-type forces.
"This testing is analogous to turning on a radio to see if it works," Hegemier said. "You don't have to check every single station on the dial. In the same way, you want to know if the building works . . . but you don't need to test every conceivable type of quake."
Already, results from the earlier steel structure and reinforced concrete tests in Japan indicate that improvements are needed both in design and workmanship.
Need for Revisions
"Some parts of the (Uniform Building Code) will need to be strengthened, no doubt about this," said Vitelmo Bertero, a UC Berkeley engineering professor overseeing the U.S. portion of those tests.
Researchers are particularly interested in the results of concrete masonry testing at UCSD. Such buildings are economical and convenient to construct and are energy efficient. Reinforced concrete masonry buildings account for 90% of all warehouses and supermarkets in California, Hegemier said. They should not be confused with buildings made of unreinforced masonry, such as hollow tile, which were common for years in California, but suffered severe damage in the 1932 Long Beach quake and have been avoided since.