Soft story structures are structures built on first stories with more than 80% open area on one first-story wall or more than 50% open area on two adjacent first-story walls.
Because of population density and high land values, mixed-use construction became prevalent, integrating soft stories so that the first story of buildings can be used as commercial real estate or parking and have a dramatically different layout than the upper stories.
These soft story structures carry a major flaw. In earthquakes, they pose a serious risk to occupants. Not only do these soft stories make the structures weaker, but they were also built to obsolete seismic standards that incorrectly predicted earthquake effect.
Many cities, such as the City of Los Angeles, have decided that soft story structures must be retrofitted to meet current guidelines for occupant safety.
Approximately 13,500 soft story structures in the Los Angeles area require seismic strengthening. In May 2016, the City of Los Angeles started sending out orders to comply to building owners, based on their retrofit priority. Owners have two years from the date of receipt to submit proof of a completed retrofit, or plans to retrofit or demolish. Owners have 3.5 years from the date of receipt to obtain a permit to start construction or demolition. Construction of the retrofit must be completed within seven years of the date of receipt.
Soft Story retrofits consist of a number of components including pre-constructed bracing, such as moment frames or shear walls, and new concrete footings. These bracings are added on the first floor to protect occupants. New footings serve to hold down the building during the shaking of an earthquake. Together, these various components complement each other to provide comprehensive earthquake resilience.