Building officials in the City of Los Angeles have identified about 13,500 buildings that are deemed to have a "soft story" and may be at risk of collapse in a major earthquake. A building with a soft story is typically a multistory building where a story is significantly less rigid than the story above. Structures of this type require a seismic retrofit.
Below are examples of structures with soft stories.
Below are examples of story structures that have failed:
A soft story structure can be retrofitted with steel moment frames, which provide the necessary rigidity and preserve the open space for parking.
Moment frames can come manufactured such as the Simpson Strong Frame and Hardy Frame. We like the design of these moment frames because they have bolt on components that can easily be serviced when any damage has incurred on the frame. These manufactured moment frames are designed to have fuses that are made to yield to prevent the rest of the frame components from being damaged during an earthquake event. These fuses can be unbolted and replaced if damaged.
Examples of Simpson and Hardy Frames:
Braced frames may also be used:
A structural/civil engineer can develop a prescriptive solution to strengthen soft stories after a careful analysis of the building to determine which areas of the building require a retrofit. At Apollo Structural we have retrofitted a few soft story apartment complexes since the City of Los Angeles released the news that these soft structures were at risk and required seismic remediation. We like to help the owner design a system that is best for the safety of their structure and their budget.