Retrofitting means making changes to a building’s systems or structure after it has been constructed and used. The aim is to enhance the building’s functionality by adding new technology, equipment, or building systems. These retrofits can result in better amenities for occupants, improved building performance, and reduced energy and water consumption.
A soft-story building is a multi-story structure with a less rigid (soft) first floor compared to the floors above. Typically, a building with a weak first floor has a large opening like a garage, large windows, or tuck-under parking. These lower floors may not withstand the impact of strong seismic activity due to unreinforced openings on the ground floor and lateral forces that push the structure from side to side.
Which buildings do they affect?
- Soft-Story Wood Frame Buildings
- Non-Ductile Concrete (NDC) Structures
Unreinforced masonry (URM) buildings need to be retrofitted for earthquakes due to the following reasons:
- URM buildings are at a higher risk of damage or collapse during earthquakes due to their construction not following modern building codes.
- These buildings are susceptible to severe damage and collapse under seismic loading.
- They are not engineered to support heavy loads, making them unsuitable for multi-story or high-rise construction.
- The lack of flexibility in URM buildings during earthquakes can lead to collapse or significant damage.
- Previous retrofit approaches had mixed success, with some performing poorly, particularly during aftershocks impacting previously damaged buildings. This shows the challenges and varying effectiveness of retrofitting methods.
- Properly retrofitted tilt-up concrete buildings demonstrate high resilience to strong earthquakes.
- Common retrofits involve adding concrete footing, gunite, steel reinforcement for columns, additional wall ties, and drag lines to distribute force effectively.
- Retrofits may include installing roof-to-wall anchors and continuity ties.
- Tilt-up concrete panels and components are cast on-site before being lifted into position.
- If you have a concrete tilt-up building built before 1996, local regulations may require that you have it retrofitted for seismic safety