Engineers look to make structures safer


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It's a test designed to exactly replicate the ground motion of the 1989 Loma Prieta earthquake -- magnitude 6.9.

"We used a ground motion, an actual movement of the ground that was recorded during the 1989 Loma Prieta earthquake, so we replayed that here on our shake table," said structural engineer Steve Pryor.

A room was built to the construction standards of 1985 or earlier, like many homes in the Bay Area. The lower portion is called the cripple wall that connects the main house to its foundation.

Another room on the left has been retrofitted by Simpson Strong-Tie, a company that produces steel connectors designed to make a building better able to withstand a major earthquake.

The key thing to notice about this test is the cripple wall built with the old style construction failed, while the one that was retrofitted did not.

"The wall that was not retrofitted failed, exactly like we've seen in many major earthquakes. The weight of the structure starts to push down on that wall, leading to a full collapse. The house would've actually fallen over, about three feet off of its foundations," said Pryor.

It's a possibility not lost on a couple that is spending $15,000 to retrofit their 70-year-old Oakland home.

"I just looked at is as part of what we needed to do to be comfortable living here," said homeowner Jennifer Ziebarth.

Sherry Niswander is the retrofit contractor.

"What's you're trying to do is get the floor system all the way connected down to the concrete. And that's called creating a load path," she said.

The goal is to keep the cripple wall of this real house from getting destroyed during the next big quake.

PROGRAMMING NOTE: Join us for a one-hour retrospective on the devastating Loma Prieta earthquake on Saturday, October 17 at 10 p.m. and Sunday, October 18 at 7 p.m. We'll look back at the damage, how the Bay Area was forever changed, and what still must be done today to prepare for the next "big one."

SPECIAL COVERAGE: Web exclusive content commemorating the 20th anniversary of the 1989 Loma Prieta quake. Includes extended interviews with reporters who covered the quake, as well as city officials and first responders who lived through it all.

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