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Structural engineers finding less is safer in design of tall buildings

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As the amount of land available for development in San Diego County decreases, local structural engineers are discovering different building/design techniques that would allow for more economical and earthquake-resistant high- and mid-rise developments.

"We're designing buildings much too strong," said Bob Englekirk, adjunct professor at the University of California, San Diego who has more than 35 years' experience as a structural engineer. He cited current California building codes as the cause of this overbuilding of structures.

Recent testing at the Englekirk Structural Engineering Center, which is part of the UCSD Jacobs School of Engineering, has revealed mid-rise buildings can be constructed using half the steel required under current codes while retaining the ability to withstand an earthquake similar in force to the Northridge quake.

"The (current) concept is if you make it (a building) 25 percent strong, it'll be better," Englekirk said. "But this is not the case."

This statement is backed by results from the center's 25-foot-by-40-foot "shake table," which applies different ground motions to the frame of a seven-story mid-rise building on the table.

During two separate tests of the seven-story frame, engineers observed how different walls and wall configurations and the decrease in steel used in the building's frame would react to ground motions. The result: The most violent earthquake shake of the structure caused only minor cosmetic damage to the building. Englekirk attributes this to the amount of steel used for the building's frame.

By using less steel "the demand on the rest of the components of the building is much lower," the professor said, adding that decreasing the amount of steel also increases the building's flexibility when a ground motion is applied.

"The net result is you save a lot of money and you produce a safer building," said Englekirk, who recently designed a 20-story building using this technology and saved nearly $1 million.

James Amundson, principal at Hope Engineering and member of the Englekirk Center Industry Advisory Board, a group of 43 structural engineering firms and associations in Southern California, said using half the steel that's required on a seven-story building would decrease costs by $1 to $2 per square foot.

The concept of using less steel appears encouraging to structural engineers who often struggle with the task of fitting all the required rebar steel into a wall.

"If the results are showing there is no net benefit (to meeting code requirements), that will streamline the construction project," Amundson said.

"I don't think we want to say the code requires more (materials than necessary), but we can do more intelligent design," said Anthony Court, spokesman for the Structural Engineers Association of San Diego and vice president of Curry Price Court Structural Engineers. Court pointed out the shake table is only testing one design method.

Although the testing results encouraged Englekirk, he expressed little optimism that these findings will influence building code requirements in the near future.

"We have such a bureaucracy in this country in terms of codes and procedures," he vented. "It's an impossible job to get some of this stuff through. It will take 20 years before (requiring less steel) gets into the code," he said.

Amundson agreed, saying right now the state is in the process of adopting new building code regulations, which will be implemented in spring 2008.

"At this stage it would be virtually impossible to get new language into the building code," he said, noting that 2011 is when the earliest new language regarding steel requirements could be accepted.

Englekirk said under the current building codes it's possible to build a seven-story structure -- similar to the one found at the shake plate -- by utilizing more scientific analysis. This requires conducting multiple tests using varying ground motions and then presenting those results for peer review prior to project approval.

Looking ahead, Amundson said the Englekirk advisory board this past week discussed new research projects, such as testing how connecting precast and cast-in-place molding would respond to varying ground motions, which hasn't been done before.

The shake table is one of 15 earthquake-testing facilities in the National Science Foundation's Network for Earthquake Engineering Simulation (NEES). The UCSD-NEES shake table is the largest in the United States and the only outdoor shake table in the world, according to a UCSD Jacobs School of Engineering release.

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