In earthquake prone California, building owners, managers, and residents constantly live under the threat of the next big trembler. Over the past decade many municipalities have identified residential buildings that may be vulnerable in an earthquake and in various forms have required (or strongly recommended) property owners to seismically retrofit their buildings. The cities of San Francisco, Berkeley, and Oakland have been the most progressive in creating legislation to deal with seismic retrofitting apartment buildings. San Francisco is currently discussing additional retrofit legislation: http://www.sfgate.com/bayarea/article/SF-wants-to-require-seismic-upgrades-4254446.php
In buildings constructed before 1978, the main issue of concern is what is known as “soft story.” In simple terms, soft story can be defined as a wood frame, multi-story building that has some type of large opening on the ground level. The opening is typically for a garage, covered parking space, or a large window. Without reinforcing the opening, the building most likely will suffer from major earthquake damage.
The two most common soft story retrofit solutions are: 1) supporting the building’s bones by installing steel reinforcements to a building’s framing and joints; and 2) minimizing the building’s movement by adding concrete sheer walls and strength to the foundation footing.
Our firm recently voluntarily retrofitted seven soft story buildings in the East Bay. Below I’ve shared some pictures from our projects to better understand the retrofit process. All seven buildings retrofitted had garages on the ground floor.
The first four photos show a building that was previously supported by metal cased concrete beams in the garage. To prevent the building from falling forward in an earthquake we poured concrete columns around the existing entry beams and tied the new columns into an enlarged concrete foundation footing.
First, the concrete footing is enlarged
Next, the new footing is poured with rebar reinforced concrete columns around the original support beams
New concrete columns replaced original wood facade columns
Here is the final product after everything was painted
Here is an example of another project we completed. This one shows a concrete shear wall shortly after it was poured
Here is the enlarged foundation footing for the shear wall above. You can see that the new footing will be reinforced with rebar and the wall will tie into it.
Lastly, here is an example of steel bracing
As you can see, seismic retrofitting can come in a variety of methods and applications. Hopefully this post was a nice introduction to the topic.