Soft story building
Encyclopedia
A Soft story building is a multi-story building in which one or more floors have windows, wide doors, large unobstructed commercial spaces, or other openings in places where a shear wall
would normally be required for stability as a matter of earthquake engineering
design. A typical soft story building is an apartment building of three or more storys located over a ground level with large openings, such as a parking garage or series of retail businesses with large windows.
Buildings are classified as having a "soft story" if that level is less than 70% as stiff as the floor immediately above it, or less than 80% as stiff as the average stiffness of the three floors above it. Soft story buildings are vulnerable to collapse in a moderate to severe earthquake
in a phenomenon known as soft story collapse. The inadequately-braced level is relatively less resistant than surrounding floors to lateral earthquake motion, so a disproportionate amount of the building's overall side-to-side drift is focused on that floor. Subject to disproportionate lateral stress, and less able to withstand the stress, the floor becomes a weak point that may suffer structural damage or complete failure, which in turn results in the collapse of the entire building.
Soft story failure was responsible for nearly half of all homes that became uninhabitable in California's Loma Prieta Earthquake
of 1989, and was projected to cause severe damage and possible destruction of 160,000 homes in the event of a more significant earthquake in the San Francisco Bay Area
, California
. As of 2009 few such buildings in the area had undergone the relatively inexpensive seismic retrofit
to correct the condition.
Shear wall
In structural engineering, a shear wall is a wall composed of braced panels to counter the effects of lateral load acting on a structure. Wind and earthquake loads are the most common loads braced wall lines are designed to counteract...
would normally be required for stability as a matter of earthquake engineering
Earthquake engineering
Earthquake engineering is the scientific field concerned with protecting society, the natural and the man-made environment from earthquakes by limiting the seismic risk to socio-economically acceptable levels...
design. A typical soft story building is an apartment building of three or more storys located over a ground level with large openings, such as a parking garage or series of retail businesses with large windows.
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
in a phenomenon known as soft story collapse. The inadequately-braced level is relatively less resistant than surrounding floors to lateral earthquake motion, so a disproportionate amount of the building's overall side-to-side drift is focused on that floor. Subject to disproportionate lateral stress, and less able to withstand the stress, the floor becomes a weak point that may suffer structural damage or complete failure, which in turn results in the collapse of the entire building.
Soft story failure was responsible for nearly half of all homes that became uninhabitable in California's Loma Prieta Earthquake
Loma Prieta earthquake
The Loma Prieta earthquake, also known as the Quake of '89 and the World Series Earthquake, was a major earthquake that struck the San Francisco Bay Area of California on October 17, 1989, at 5:04 p.m. local time...
of 1989, and was projected to cause severe damage and possible destruction of 160,000 homes in the event of a more significant earthquake in the San Francisco Bay Area
San Francisco Bay Area
The San Francisco Bay Area, commonly known as the Bay Area, is a populated region that surrounds the San Francisco and San Pablo estuaries in Northern California. The region encompasses metropolitan areas of San Francisco, Oakland, and San Jose, along with smaller urban and rural areas...
, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
. As of 2009 few such buildings in the area had undergone the relatively inexpensive seismic retrofit
Seismic retrofit
Seismic retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. With better understanding of seismic demand on structures and with our recent experiences with large earthquakes near urban centers,...
to correct the condition.