With the inevitable threat of earthquakes in California, many property owners have pursued seismic retrofitting projects to help strengthen the structural integrity of their properties. Last week, Felson Companies completed a voluntary seismic retrofit of two buildings at Whitman Green Apartments in Hayward.
The project at Whitman Green was pursued because the buildings are two-story, wood frame structures built over ground floor garages. Their structural integrity was concerning because of the configuration of the ground level parking. The offset layout of the buildings allowed for engineering improvements to be made to better tie the two building halves together. The project was designed by Clausen Engineers of Emeryville. “Every seismic event is an opportunity for engineers to learn more about the performance of buildings during earthquakes. Our knowledge base has increased significantly in the time since many of the homes and apartment buildings in the Bay Area were constructed. If the opportunity is available to an owner, a seismic retrofit can be a wise investment for their property” advises Patrick Hines of Clausen Engineers.
Seismic strengthening was achieved at both buildings at Whitman Green by installing a threaded steel rod and strapping system through the width of the entire building, reinforcing a major load bearing wall, and installing a new exterior wing wall. “Seismic projects are typically very thorough, and this one was no exception. We added additional shear to the load bearing wall in the garage level and 61 clips per building to tie the load bearing wall to the ceiling joist above,” said contractor Peter King of King Construction. Movement in an earthquake will be minimized with these precautions because the threaded rod, clips, and strapping system will act like a seat belt for the entire building while the exterior wall will act as an anchor to the offset portion of the building.
With the completion of this job, Felson Companies has now seismically retrofitted 13 buildings in Alameda County. Many property owners tend to be very weary of pursuing seismic retrofitting because of cost, architectural changes, and perhaps design complexity. Many property owners wait until municipal regulations require a retrofit. Contrarily, Felson Companies has retrofitted all of their buildings voluntarily. “We’ve been successful in these projects by conducting a significant amount of pre-construction due diligence and selecting engineers and contractors who are experienced, budget conscious, and can explain their decision making in a straightforward manner” said Blake Felson, who spearheaded the project for Felson Companies. Although we may never be able to accurately predict when the next earthquake will occur, we can most likely predict how a building will move in an earthquake. If done accurately and correctly, seismic retrofitting should help to minimize that movement.