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Structural Engineers Find Ways to Reinforce Old Buildings to Make Them Earthquake-Proof


A powerful earthquake in Iran killed at least 500 people this week and left thousands living in temporary shelter. Officials say the death toll could go higher as rescue workers search for more survivors.The epicenter of the quake was not far from the ancient city of Bam, where more than 30,000 people died in a similar earthquake in December 2003.

Rebuilding after this kind of devastation can take years. Many damaged buildings in earthquake zones are made of brick, with weak bracing. But there are ways of reinforcing these old structures to make them safer.

Five years ago a magnitude 7.4 earthquake destroyed much of Ismit, Turkey, killing more than 17,000. The high number of deaths was the result of inadequately reinforced buildings coming down on people.

Engineers have studied structures in the aftermath of these kinds of strong earthquakes to see how new and existing buildings can be made to withstand seismic forces.

In the U.S., strong structures begin with the enforcement of good building codes, something often lacking in the developing world.

William Wallace is a structural engineer at Englekirk and Sabol, one of the leading firms in the U.S. that designs seismic reinforcement. "A lot of the countries don't have specific building codes, and the codes have been established by independent groups to make buildings safe for people," he said. "As the building is being built by the contractors there's a multitude of inspections that are required by the codes."

Masonry without adequate bracing is the biggest problem for buildings when earthquakes occur. "There are several types, in general, that require strengthening," said Mr. Wallace. "The unreinforced masonry structures, this is basically a brick building that doesn't have any steel reinforcing in it."

But it is not practical to tear down and replace most of these inadequate buildings. Mr. Wallace adds, "Just because of the shear volume of the number of buildings is a very difficult economic reality to face. Every building is different and each requires it's own seismic solution. With each structure we really have to do some due diligence in evaluating what the strengths and weaknesses of the building are."

One solution is called base isolation where a shock absorbent material is placed in columns and foundations. The Los Angeles City Hall has been retrofitted with base isolation and the new Los Angeles Cathedral included them in its original design. Mario Cipresso, the construction administrator, shows one of the buildings recently renovated and structurally upgraded. by adding 'X' braces designed to transfer all the forces, triangulate them through the trusses.

Jeff Rouze is a Los Angeles developer who is renovating an 87-year-old historic apartment building in Hollywood that suffered earthquake damage. "It had damage in the Northridge earthquake in 1994. This is a typical earthquake caused crack. This is a supporting beam for what they call a shear wall, which is a wall that would accept earthquake energy. And as you can see it's under stress and it's bowed. And we have had to reinforce it here until we can install a new beam overhead and some columns to transfer the load," he said.

The building requires new support beams and columns.

The building also had something called 'shock-crete' applied. This process reinforces existing walls with a new layer of steel rods and concrete. Shock-crete is a likely solution for the many masonry structures in the developing world. Mr. Rouze points out the new wall. "This is the new reinforcing wall, it's called shock-crete," he said. "It's a sprayed on concrete over rebar. So there is steel inside this that reinforces this wall."

Seismic resistant building adds cost, cost that poor countries find hard to meet. But the cost in lost lives from earthquakes is even greater.

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