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Soft story buildings can collapse with seismic activity.
In most earthquakes, many reinforced concrete structures suffer from minor to catastrophic damage. The most commonly observed damage is the cracking and falling of walls. But the most striking of these observations is the structural failures of multi-story buildings, which have soft ground floors used for parking, called the "soft story."
Since buildings with sound construction should not experience any major damage caused by ground motion, possible damage is due to inherent weaknesses in the structural system, design, detailing, poor material quality and unsound construction practice.
Why Are Soft Stories Inherently Weak?
A large opening in at least one wall, and a lack of central supports, make soft stories more susceptible to lateral forces from a large earthquake. When they fall, the second floor pancakes the first floor.
Shear wall panels won't help much. Soft-story buildings need to be retrofitted with specially designed steel reinforcements.
Damage to reinforced concrete building structures can be attributed to a combination of the following reasons:
Soft Story buildings are inherently weak because they lack proper structural support.
1. Soft story effects
2. Poor detailing of structural joints
3. Inadequate reinforcing steel
4. Inappropriate anchoring of beam and slab reinforcement
5. Insufficient reinforcing steel in columns with large aspect ratio
According to Caltech, there are more than 20,000 soft-structure apartment buildings in the City of Los Angeles alone. Only 800 of those have been seismically retrofitted, according to the Los Angeles Department of Building and Safety.
Some Southern California cities have mandated that buildings be retrofitted to prevent collapses like the one at Northridge Meadows Apartments, where 16 people died during the Northridge earthquake. But progress on such renovations has been painfully slow — and almost non-existent.
These are the steps to reinforce a soft story building:
1. The concrete slab is broken up.
2. New reinforcement beams are placed underneath the old concrete poles that hold the
3. New concrete is being poured to hold the new beams.
4. The structure is stable again.
The concrete has been poured, placed, and dried, and now this building has soft story reinforcement, enabling it to resist the destructive forces of any major earthquake in Southern California.
Wood forming is placed to get ready to pour concrete at the steel rebar area.
The entire row of steel support beams are connected through steel rebar reinforcement at the clean cut section of the concrete slab.
Steel Rebar Reinforcement is placed and will be embedded within the new concrete.
The slab area is being hallowed for new concrete. The spaces between the steel support beams will be removed in order to connect them for engineered load bearing support.
The steel beams are supported at the base with underpinning, which is concrete footing reinforced with steel rebar.
New steel support beams are added and temporary wood shoring beams hold the structure in place during construction.
The concrete area is cleaned of all unwanted debris.
First, excavation is performed to install support beams. Saw cut, demo, and remove concrete.
Many dwellings are in danger of collapsing with a big enough earthquake. Lives, cars, and property are at risk.
Close Up View of Unreinforced Soft Story Apartment
Many apartments in Los Angeles are weak at the soft story parking structure.