Last month, The Applied Technology Council released a report on 156 buildings in SF standing over 240 feet. This report also included unconstructed buildings that have received a construction permit.
Back in 2017, the City published a Tall Buildings Safety Strategy, however, it has since been updated to include input from the engineering communities.
What Was The Goal?
To propose recommendations on issues that pose a seismic risk to SF’s tall buildings.
Here are the issues that the report focused on:
1a. SF Building Code’s minimum requirements are not enough for geotechnical site investigations and foundation design. The minimum requirements do not go into full detail to address geotechnical conditions (size/weight of new buildings, how sites are investigated to assess building behavior and response to earthquake motions)
The Department of Building Inspection (DBI) should require an Information Sheet that addresses the best practices for the following:
- “Settlement design and analysis criteria”
- “Quality Assurance/Quality Control for foundation systems”
- “Foundation design and other countermeasures for soil liquefaction and lateral spreading”
- “Shoring and dewatering design and analysis criteria”
- “Lateral earthquake resistance of deep and shallow foundations”
- “Site characterization and exploration”
1b. A new tall building designed to current standards might take 2-6 months after an earthquake to repair damages. The extent of the damage depends on the building location, geologic conditions, and the structural and foundation systems.
The DBI should develop an Administrative Bulletin (with building codes amended as needed) that works with the City’s goals towards tentative recovery while including requirements around recovery-based seismic design specifications like unexpected ground motion, elevator systems, exterior cladding/partition walls. Even the recommendations by the ATC would cut down that recovery time to 3 months, which is still too long.
2a. In 1994, the Loma Prieta earthquake caused damage to welded steel moment frame structures in Los Angeles. Although there wasn’t much data recorded for damages in San Francisco, what was recorded revealed that some steel SF buildings had undetected damage from the earthquake.
The Department of Building Inspection should work as a community setting to develop “a New Administrative Bulletin to interpret provisions of the SF Existing Building Code as they apply to post-earthquake inspection and evaluation of welded steel moment frames.”
2B. When tall buildings have alterations or occupancy has changed, certain scopes can be exceeded by SF code provisions. The SF Building Code triggers seismic upgrade only when two-thirds has been altered. The code has not been amended and tall buildings easily avoid any examination or reevaluation. “Therefore, even the most collapse-prone tall buildings almost never receive the scrutiny intended by the code.”
A revision between triggers and triggered scope from an alteration like setting lower triggers is recommended for recovery planning and building resilience.
2C. The ATC points out that there isn’t much earthquake insurance available for commercial and residential buildings. “Furthermore, when available, the insurance coverage is often limited to a small fraction of the building replacement cost, raising questions about the ability to repair and recover after a damaging earthquake. Insurance or other resources to cover losses suffered by the neighbors of a tall building or costs to the City (for debris removal or emergency protective measures) are also unclear.”
To protect building owners and their communities’ recoverability, the City should recommend minimum levels of insurance or collateral and they should research limitations of what financial capital should be available.
2D. In case of a fire, many highrise buildings usually use an internal sprinkler system, however, the City’s water supply could be disrupted in the event of an earthquake.
A study by The SF Fire Department and Department of Emergency management should “evaluate the adequacy of automatic fire suppression and occupant evacuation systems in tall buildings following a significant earthquake.”
- Testing mainly the building’s secondary water supply
- and the building code provisions of the elevator evacuation process.
3. Actions for Reducing Seismic Risk Following Earthquakes
3A. Volunteer inspectors “post” buildings with colored placards by The Safety Assessment Program and run by the California Office of Emergency Services. However, the SAP procedures are generic and not suited for most tall buildings.
Tall San Francisco buildings should have their own procedures regarding damage estimates, placard use and text, limits on rapid evacuation, and exterior-only inspection.
3B. The Building Occupancy Resumption Program was created by the DBI. With BORP, arrangements were made in advance by building owners to contract inspectors for post-earthquake safety inspections. While BORP helps tall buildings apply guidelines from the general Safety Assessment program, it could still be enhanced for more efficient maintenance.
- Simulation-based training for staff, inspectors, DBI staff, and building.
- Updated BORP instructions and procedures for consistency and practicality.
- Implementation of FEMA 352, Recommended Postearthquake Evaluation and Repair Criteria for Welded Steel Moment-Frame Buildings, for welded steel moment frame structures.
- Make BORP a requirement for all new tall buildings including various implementations.
3C. As of now, many post-earthquake procedures are not up to date and inconsistent, including the roles for city departments.
The DBI, the Department of Public Works, and Department of Emergency Management should work together to update the Earthquake Annex of the San Francisco Emergency Response Plan.
3D. “While the latest requirements in the San Francisco Building Code are rational for most buildings, for larger structures, they can become disproportionately expensive and disruptive; if repairs to many large buildings are triggered, the aggregate impact can affect the City’s overall recovery. San Francisco’s code amendments might exacerbate the problem by not allowing the use of reduced loads typical for retrofits.”
Update traditional amendments in coordination with the California state code. The Building Inspection Commission and the Office of Resilience and Capital Planning should consider if certain building code provisions should be lifted in regards to repair-triggered retrofits. “The study should consider typical San Francisco buildings, ideally with a scenario that considers the effects of multiple buildings on downtown recovery.”
3E. Update Administrative Bulletin 099 and specify how it applies to tall concrete structures. As of now, AB-099 is due for updates and while AB-099 does not apply to many tall buildings, it does apply to all concrete buildings.
The Department of Building Inspection should update AB-99 to apply code provisions for newer buildings and reference standards.
3F. FEMA 352, Recommended Post-earthquake Evaluation and Repair Criteria for Welded Steel Moment-Frame Buildings is a publication that provides recommendations for post-earthquake inspection procedures for damage in steel moment-frame structures. However, FEMA 352 is not fully referenced in SF codes and steel moment-frames are in most of SF’s tall buildings.
To implement FEMA 352, the Department of Building Inspection should build an Administrative Bulletin that clarifies procedures that the DBI will accept for emergency evacuations in coordination with Rapid and Detailed Evaluations using ATC-20 (a building safety evaluation form by the Applied Technology Council).
3G. In order to protect an area around a damaged building, cordons or barricades are often used. The current general guidance for cordons can mean an increase in cordon distance which could lead to nearby buildings and infrastructure to close.
Create new and update older protocols for cordoning in a damaged building area. These protocols for tall buildings should be current practices and be based on the effects they have on neighborhood safety and recovery.
3H. When aggressive retrofit triggers and mandates are expensive, a recovery plan should serve as an alternative. While BORP does provide recovery for non-severe building scenarios, but it has not been used widely enough for a thorough recovery of a densely packed neighborhood.
Identify the buildings that are most significant to the City’s recovery and create a basic recovery plan. With a mandate of the filing of each building’s information, a building-specific recovery plan could help facilitate BORP benefits without much cost from building owners.
4. Actions to Improve the City’s Understanding of its Tall Building Seismic Risk
4A. A database was created with info (including building location, height, occupancy, age, construction material, etc) on buildings 240 feet or higher whether constructed or permitted. While keeping track of all these components in the database are important, the City will need to maintain and expand it.
The ORCP owns the database and should work with the Department of Building Inspection as well as DataSF to expand and maintain the database efficiently. This includes the harvest of building data after inspections or permits are issued, making the database publicly available, and expanding the database to include buildings taller than 75 feet.
4B. The present study discusses how tall building damage and the effect it has on the buildings themselves. However, the report does not address the effects of damaged tall buildings might have with nearby buildings that are mid-rise and low-rise. It also fails to discuss the resource demands capacities of residents, businesses, etc.
For ideas that support the neighborhood to come together, a recovery plan by the City Administrator should be put in place based on present-day findings. The study will include an estimated level of functional loss, the time it will take for re-occupancy after an earthquake, and alternative plans for standards of habitability.
Terms and Abbreviations:
Applied Technology Council (ATC): A California nonprofit that evaluates the effects of natural hazards and identifies what should be improved for engineering efforts.
FEMA 352: “FEMA-352 – Recommended Postearthquake Evaluation and Repair Criteria for Welded Steel Moment-Frame Buildings. This publication provides recommendations for performing postearthquake inspections to detect damage in steel moment-frame buildings following an earthquake, evaluating the damaged buildings to determine their safety in the post-earthquake environment, and repairing damaged buildings.”
Office of Resilience and Capital Planning (ORCP): The city’s program that plans and finances projects that benefit the City’s neighborhoods, buildings/infrastructure, and residents.
Building Occupancy Resumption Program (BORP): Created by the Department of Building Inspection, this program allows SF building owners to contract engineers to precertify private post-earthquake inspection.
Building Inspection Commission (BIC): oversees the enforcement of the “City and County’s Building, Housing, Plumbing, Electrical, and Mechanical Codes, along with Disability Access Regulations.”