Santa Cruz Victorians Become Earthquake Experiment
In 1989, on the corner of Center and Elm streets near downtown Santa Cruz, California, architect Michael O'Hearn unwittingly created a laboratory for the study of seismic retrofit.
On that corner, at 214 and 210 Elm Street, were two identical Victorian style homes. According to O'Hearn the twins were built 90-100 years ago, by the same builder, with identical materials, using the same construction techniques.
By 1984, when O'Hearn bought them, both houses had been through multiple remodels. Originally designed as single family homes, #210 had become a five-plex and #214 a four-plex. O'Hearn remodeled the pair yet again.
He started with #210, installing plywood structural panels as a shear element on cripple-wall framing. Also he bolted the sill plate to the foundation. Unfortunately, there was no time to install new panels in #214 before Oct.17, 1989 - when the magnitude 7.1 Loma Prieta quake struck causing massive damage in Santa Cruz and through out the San Francisco Bay Area.
The building at 214 Elm came apart in four sections, O'Hearn said. "Five people were in the house when the quake struck, but luckily, no one there was seriously injured."
By contrast #210, identical except for its plywood panel shear walls and bolted foundation, suffered only minor damage.
Said O'Hearn, "The one that we had done some seismic work on (#210) probably cost us $5,000 to repair after the quake. The other one (#214) cost us $260,000 to repair. The whole building had to be jacked up and slid back together on a new foundation."
214 Elm Street had served as the control element in this unexpected experiment, the results of which confirmed O'Hearn's thinking on the value of seismic retrofit.
"For homes more than 20 years old located in areas of seismic activity, I strongly urge owners to carefully consider seismic retrofit, " O'Hearn said. "It's cheaper to retrofit now than to repair after a quake."
Homeowners guide to earthquake retrofit
APA, The Engineered Wood Association
