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Soft Story Retrofit

The structural expertise you can rely on to efficiently improve seismic resilience and ensure compliance.

As part of Partner’s structural engineering practice, we offer services to help property owners comply with mandatory retrofit ordinances. More specific than a general Seismic Risk Assessment, evaluation for a Soft-Story Retrofit addresses a level of a building that is significantly weaker than the others. Our engineers have years of experience in structural engineering and design for seismic hazards, including soft story retrofits. Partner also understands how soft story retrofitting fits in with broader standards such Fannie Mae, Freddie Mac, and HUD, as well as ASTM Seismic Standards E2026 and E2557.

What is a Soft Story?

The term “soft-story” refers to one level of a building that is significantly more flexible or weak in lateral load resistance than the stories above it and the floors or the foundation below it (70% or greater reduction from one floor to the next according to the modern, International Building Code (IBC) definition). This condition can occur in any of the conventional construction types and is typically associated with large openings in the walls or an exceptionally tall story height in comparison to the adjacent stories. These soft stories can present a very serious risk in the event of an earthquake, both in human safety and financial liability.

The common sources of seismic vulnerabilities include:

  • Ground floor tuck-under parking beneath wood-framed residential apartment buildings.
  • Tall first floor story heights, typical in older mid-rise and high-rise commercial office buildings where the first floor is generally twice the height of a normal floor above.
  • Retail buildings with the store front constructed mostly of glass.
  • Multi-use buildings in urban environments (e.g. San Francisco Bay Area and the Seattle Metropolitan Area) with commercial retail tenants on the ground floor with large glass store fronts and apartment residences above.

City Ordinances Requiring Seismic Retrofit

Retrofit ordinances can be complicated and city specific, Partner has expertise navigating them and guiding clients through the myriad finance options.

The San Francisco Mandatory Soft-Story Retrofit Ordinance, born out of the San Francisco Community Action Plan for Seismic Safety (CAPSS), targets wood frame buildings built before 1978 with 3 or more stories and 5 or more residential units with significant ground floor openings. These buildings maybe subject to the ordinance and required to be retrofitted to meet or exceed the following design standards: FEMA P-807, ASC 31/41, or IEBC Appendix A4. The financing options range from government backed bonds and city backed loans to retrofit cost transfer.

The City of Los Angeles passed a mandatory retrofit ordinance. The LA ordinance will require the structural strengthening of two of the city’s most vulnerable building types: wood framed soft-story buildings built before 1978 and non-ductile concrete buildings built before 1977. Finacing and funding options are being explored.

Berkeley, Fremont, San Jose, Oakland, San Leandro, Campbell, Burbank, and Santa Monic, Portland, Seattle and other communities have implemented or are drafting mandatory and voluntary seismic retrofit programs and ordinances. The list of cities considering or enacting retrofit ordinances is likely to continue growing and Partner is committed to keeping up to date with their requirements.

Retrofit Options

Partner is expert in designing retrofit options; we combine our understanding of our client’s business with our structural engineering experience to arrive at a retrofit solution. Some of the common methods employed to retrofit soft-stories include the installation of:

  • Plywood Shear Walls
  • Concrete Shear Walls
  • Braced or Moment-Resisting Steel Frames
  • Cantilevered Steel Columns
  • Foundations and Grade Beams
  • Foundation, Roof and Wall Anchors
  • Continuity Ties
  • Collector Detailing
  • Strenghtening Unreinforced Walls
  • Base Isolation
  • Jacketing of Columns