SAN FRANCISCO TALL BUILDINGS STUDY Disclaimer: While the information presented in this report is believed to be correct, the Applied Technology Council assumes no responsibility for its accuracy or for the opinions expressed herein. The material presented in this publication should not be used or relied upon for any specific application without competent examination and verification of its accuracy, suitability, and applicability by qualified professionals. Users of information from this publication assume all liability arising from such use. San Francisco Tall Buildings Study Prepared by APPLIED TECHNOLOGY COUNCIL 201 Redwood Shores Parkway, Suite 240 Redwood City, California 94065 www.ATCouncil.org Prepared for City and County of San Francisco Office of Resilience and Capital Planning Brian Strong, Chief Resilience Officer and Director Danielle Mieler, Principal Resilience Analyst San Francisco, California ATC MANAGEMENT AND OVERSIGHT PROJECT TECHNICAL COMMITTEE Ayse Hortacsu John D. Hooper (Task Leader) Justin Moresco David Bonowitz Gregory Deierlein PROJECT WORKING GROUPS Shahriar Vahdani Carlos Molina Hutt Preetish Kakoty CITY AND COUNTY OF SAN FRANCISCO Anne McLeod Hulsey TALL BUILDINGS EXECUTIVE PANEL Alireza Eksir Monfared Naomi Kelly (Chair) Max Rattie Mary Ellen Carroll Wen-Yi Yen Kathryn How Tom Hui TASK REVIEW PANEL Brian Strong Mark X. Haley William Walton December 2018 CITY AND COUNTY OF SAN FRANCISCO TALL BUILDINGS STAKEHOLDERS Board of Supervisors Business District 3 San Francisco Chamber of Commerce District 6 Real Estate Private Engineers and Architects Real Estate Advisory Services DBI Code Advisory Committee Heller Manus Architects Community and Non-profit Organizations Building Inspection Commission SPUR HOK BOMA Maffei Structural Engineering The East Cut Community Benefit District BXP SEAONC AB 82/83 Code Advisory City and County of San Francisco Staff Committee Department of Building Inspection Fennie+Mehl Architects Real Estate Division Department of Emergency Management Developers Planning Department San Francisco Apartment Owners Fire Department Association SFPUC Tishman Speyer Public Works Boston Properties Office of Resilience and Capital Planning Preface In 2010, the Applied Technology Council (ATC) concluded the Community Action Plan for Seismic Safety (CAPSS) for the City and County of San Francisco, identifying risks from future earthquakes and developing recommendations to reduce the most significant earthquake impacts. As a result, in 2011, the City published the CAPSS Earthquake Safety Implementation Program Workplan 2012-2042 that anticipates actions for broad groups of new and existing buildings throughout the city. In considering this broad workplan, it became clear that special consideration would be needed to address the unique characteristics of San Francisco’s tall buildings. In 2017, ATC was awarded a contract to develop an inventory of tall buildings in San Francisco and to review the impact of earthquakes on such buildings. ATC is indebted to the members of the Project Technical Committee who served as the principal authors of this report, including David Bonowitz, Greg Deierlein, John Hooper (chair), and Shariar Vahdani, and the members of the Working Groups consisting of Carlos Molina Hutt, Anne McLeod Hulsey, and Wen-Yi Yen. Preetish Kakoty, Alireza Eksir Monfared, and Max Rattie also contributed to the Working Groups. ATC gratefully acknowledges Mark Haley and Bill Walton for their review of Part 6 of this report. The names and affiliations of those who contributed to this report are provided in the list of Project Participants at the end of this report. ATC also gratefully acknowledges guidance and support provided by Brian Strong and Danielle Mieler of the City’s Office of Resilience and Capital Planning. The Tall Buildings Executive Panel, consisting of Mary Ellen Carroll, Kathryn How, Tom Hui, Brian Strong, and Naomi Kelly (chair) provided advice at key stages of the work. ATC staff members Justin Moresco and Carrie Perna provided project management support and report production services, respectively. Ayse Hortacsu Jon Heintz ATC Director of Projects ATC Executive Director ATC-119-1 Preface iii Summary Recommendations In 2011, the City and County of San Francisco published the CAPSS Earthquake Safety Implementation Program Workplan 2012-2042 as a result of the Community Action Plan for Seismic Safety (CAPSS) in response to Mayor Newsom’s Executive Directive 10-022. Workplan 2012-2042 anticipates programs for broad groups of new and existing buildings throughout the City. Looking ahead, the City recognized that within each broad group, some buildings would need special attention through exemptions, programmatic solutions, or specific technical criteria, to make the work feasible. One such subgroup comprises the City’s “tall buildings.” In tall buildings, difficult exterior access, multiple tenants and uses within a building, and their sheer size complicate evaluation and retrofit. Their structural systems preclude generic performance assumptions and prescriptive engineering solutions. Damage to a tall building can pose risks well beyond its own footprint. Their high concentration downtown poses an aggregate risk to neighborhood and citywide recovery not presented by other building groups. Perhaps most important, San Francisco’s new and existing tall buildings represent a dominant portion of the City’s business sector, and increasingly house residents as well. For these reasons, the City initiated the first project in the nation to consider the impact of earthquakes on tall buildings. The project conducted investigations in seven focus areas under separate tasks. This report documents the complete findings and recommendations of each task, and the recommendations are summarized below. An inventory developed for the project identified 156 buildings that are 240 feet or taller, either constructed or permitted for construction, primarily located in San Francisco’s northeast neighborhoods (Supervisorial Districts 3 and 6). Approximately 60% of these buildings contain primarily business uses, while the others are predominantly residential. The recommendations presented here flow from a study of these tall buildings, but most are also applicable to a wider set of buildings supporting similar functions or posing similar risks. Tall buildings, even in downtown San ATC-119-1 Summary Recommendations v Francisco, are only part of a neighborhood’s building stock, and from a public policy perspective, their earthquake performance is bound up with that of the shorter buildings around them. Each recommended action identifies one or more City departments to lead its implementation. However, implementation of any new policy is assumed to involve appropriate coordination with other City departments, outside experts (as needed), and other stakeholders. Some recommended actions require enactment of legislation by the Mayor and Board of Supervisors or action by the Building Inspection Commission and can only commence after these approvals. Sections 1 through 4 below summarize the findings from the study in issue statements and describe the associated recommendations to address the issue. Section 5 presents the recommendations in a table format showing different aspects of each recommendation, including potential implementation timeframe, relationship to Workplan 2012-2042, City department responsible for implementation, and the relationship of recommendations to Parts of the project report for reference. The Summary Recommendations were originally published by the City as part of the Tall Buildings Safety Strategy on October 4, 2018. They have been updated in response to feedback from the structural engineering community. The specific changes are as follows: Recommendation 2A was modified to include a clarification that the repair provisions of the San Francisco Existing Building Code should be applied in accordance with a future Administrative Bulletin that defines appropriate triggers and other indicators of potential damage. Recommendation 2B was expanded to include the addition of triggers that apply when buildings are purchased or leases are renewed. In addition, the issue statement was expanded to include change of occupancy triggers. 1. Actions for Reducing Seismic Risk Prior to Earthquakes – New Buildings 1A. Develop Regulations to Address Foundation and Geotechnical Issues Issue: The San Francisco Building Code sets minimum requirements for geotechnical site investigations and foundation design. Because they are minimum requirements, they do not fully address all of the geotechnical conditions found in San Francisco. Over the past several decades, the San Francisco geotechnical community has developed best practices for vi Summary Recommendations ATC-119-1 geotechnical evaluation and foundation design, but these are not yet codified. Many of the new tall building developments are challenging even these best practices due to unique soil conditions, the size and weight of the new buildings, and the sophisticated site investigation and the analysis approaches being used to assess overall building behavior, including building response to extreme earthquake ground motions. Recommendation: To help reduce the risk associated with these geotechnical challenges, the Department of Building Inspection (DBI) should develop an Administrative Bulletin or Information Sheet (with building code amendments as needed) with acceptable practices on topics including the following: Settlement design