Structural strengthening is the process of increasing the structural integrity of a building in order to resist seismic racking, or for developing increased capability to carry additional load such as construction of additional floors.
What is the process of seismic retrofitting?
The operations usually involve the construction of a primary resisting structure such as a Moment Frame, Braced Frame, Shear Wall and or High Strength Diaphragm. The building is then connected to these resisting structures via structures called collectors for shear transfer. Often, additional reinforcing connections between the existing building components such as foundation to frame and between beams and posts are recommended as well.
When a building is being strengthened to resist earthquake, the process is also called Seismic Upgrade or Seismic Retrofit. More about this mandatory San Francisco ordinance, here.
Among the commercial structures, the most vulnerable are buildings with soft story conditions as well as un-reinforced masonry buildings.
Soft story condition refers to multi story buildings with a ground level design, mostly comprised of columns and short span walls to accommodate retail windows and garage openings. The upper levels are typically used as offices or apartments.
See our soft story seismic work on Fillmore Street.