Engineers prepare for quakes in Wisconsin

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Sean Ryan
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As the American Society of Civil Engineers updates its seismic building standards, places such as Wisconsin pose a special challenge.

Few earthquakes affect the state, leaving researchers to give their best guess on how much reinforcement buildings need, said Donald Dusenberry, chairman of the ASCE committee that is revising standards for engineers to calculate structural pressures on buildings.

“Bottom line is we come up with our best judgment,” said Dusenberry, senior principal in the Boston office of engineer Simpson, Gumpertz & Heger Inc. “But it is a smearing or a representation for areas that don’t have earthquakes based on areas that do have earthquakes.”

As evidence of Wisconsin’s scant little history of earthquakes, people in Milwaukee in April 2008 felt vibrations from a quake in southern Illinois, but the last earthquake that centered on the city occurred in 1947.

The seismic section of the ASCE standards sets earthquake forces for different areas of the country. The goal: Ensure that every building has an equal chance of surviving the level of quake most likely to affect its area.

A complicated system is used to determine how much back-and-forth shaking buildings must be designed to withstand during quakes. The forces engineers use to test buildings are based on the type of soil under the project site, the size of the building and the purpose of the development. Hospitals, for example, must be able to withstand stronger seismic forces than strip malls.

For a normal box-shaped building — as opposed to a complicated structure such as the Milwaukee Art Museum addition — the seismic standards have little effect on design or project cost, said Jamison White, head structural engineer for Berners-Schober Associates Inc., Green Bay. He recalled designing Kellner Hall, an athletics building near Camp Randall in Madison, and having to shore up the structural joints on one side of the building to withstand quakes.

But, White said, earthquake tolerance has little bearing on building design and is not a focal point for owners or designers on most projects.

In Wisconsin, the seismic forces used for building structural calculations are very low, but there’s always a chance that a large-scale earthquake will strike again, said Christopher M. Foley, professor of civil engineering at Marquette University. The New Madrid fault line, which stretches from southern Illinois through Missouri, could generate earthquakes that could shake Milwaukee more than any structural calculations anticipate, he said.

The last major New Madrid earthquake was in 1812.

“When it’s going to occur again, there are more guesses than you can shake a stick at,” he said.

Foley said there’s nothing stopping engineers or project owners from accepting extra costs to reinforce a building in case the big one hits.

“It’s not really a practical thing,” he said. “It’s kind of an ethics thing.”