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THE UTAH GUIDE FOR THE SEISMIC IMPROVEMENT OF UNREINFORCED MASONRY DWELLINGS Ut

THE UTAH GUIDE FOR THE SEISMIC IMPROVEMENT OF UNREINFORCED MASONRY DWELLINGS Utah Seismic Safety Commission Existing Buildings Committee Second Edition 2016 Utah Seismic Safety Commission Existing Buildings Committee Second Edition 2016 THE UTAH GUIDE FOR THE SEISMIC IMPROVEMENT OF UNREINFORCED MASONRY DWELLINGS The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings PREFACE This publication is prepared for information purposes to assist owners of unreinforced masonry (URM) dwellings (homes) in gaining a better understanding of the seismic improvement of their dwellings. It is recommended that owners enlist the expertise of a Utah-licensed contractor or repair specialist prior to the implementation of the fixes illustrated herein. While several generalized dwelling types are addressed in this publication, each home is unique and for greater assurance and reliability, a Utah- licensed Professional Engineer and/or Architect should be retained to design and detail specifically tailored corrective measures. This document is intended for general informational use by homeowners and small residential contractors, and if any non-dwelling building or other non-residential commer cial building repair is being considered, the owner should certainly involve a Utah-licensed Structural Engineer. This publication is not to be used as a construction document. The agencies and businesses involved in the design and preparation of this publication accept no responsibility for rehabilitation work or any action taken based on information found in this publication. Unreinforced masonry and lightly reinforced masonry dwellings were typically constructed prior to 1975. Beginning in 1973, the building codes began to introduce more significant seismic requirements. Such dwellings were commonly constructed using solid masonry bearing walls without adequate steel reinforcing. As a result, URM dwellings lack the ductility required to absorb seismic energy in a signifi cant earthquake. Often, the dwellings are quite brittle and lack proper attachment between the walls and roof, preventing the roof from stabilizing the wall. In multi-story dwellings, the same concept applies to attachments between the floor and walls. Because of these structural deficiencies, URM dwellings can quickly fail during earthquakes and should not be expected to perform adequately during a large earthquake. While it is impractical to make any dwelling earthquake proof, the techniques shown in this publication are intended to generally improve the seismic performance of a URM dwelling. Potential earthquakes have a wide range of magnitudes and other characteristics and it should be expected that damage can still occur, even after the upgrading of URM structures. Moderate magnitude earthquakes occur peri odically and, although minor damage is usually associated with these events, they have been known to cause major damage. High magnitude earthquakes (such as, above magnitude 6.75) have been known to cause damage to even strengthened or partially-strengthened structures. Generally, the more seismic upgrade measures that are taken to improve any given structure, the greater the potential reduction in damage due to the earthquake. The purpose of this guide is to minimize the possibility of a catastrophic failure of a dwelling by the implementation of seismic upgrades, all in an effort to mitigate the loss of life during a major earthquake. iii The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings ACKNOWLEDGMENTS One important strategy identified in the Utah Seismic Safety Commission’s (USSC) 1995 publica tion A Strategic Plan for Earthquake Safety in Utah was the need to provide seismic strengthening of existing dwellings. The USSC partnered with the Structural Engineers Association of Utah (SEAU) in advocating the statewide adoption of existing dwellings building codes and other regulations. In the 2008 progress report, Earthquake Safety in Utah, the USSC describes it’s action plan and target focuses that include: learning about, building for, and living with earthquakes. Under the building for earthquakes focus, is an initiative for improving vulnerable dwellings. This guide is the outcome for this initiative in that seismically upgraded dwellings will reduce the loss of life and property in the event of an earthquake. The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings (Utah Guide) has been reviewed, expanded, and updated by the combined efforts of the SEAU, the USSC, the Utah Division of Emergency Management (UDEM), and the Federal Emergency Management Agency (FEMA). A special thanks to the SEAU/USSC Existing Building Committee (EBC) Chairs, Glen Palmer and Barry Welliver, for managing this project, and to the members of the Utah Guide Subcommittee of the EBC: Brian Warner, Zach Hansen, Curtis Earl, Roger Evans, and Bob Carey, who have donated their time and expertise. FEMA and the UDEM, through the Earthquake Preparedness Program, provided funding for the update to the original Utah Guide, resulting in this second edition. iv The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings Acknowledgments (Second Edition – 2016) Contributors Structural Engineers Association of Utah Utah Seismic Safety Commission, Existing Buildings Committee Existing Buildings Subcommittee on the Update of the Utah Guide Roger Evans, Past USSC Chair Glen E. Palmer, S.E., EBC Chair Barry H. Welliver, S.E., Past EBC Chair Technical Editing Subcommittee Members: Brian Warner Zach Hansen Curtis Earl Glen E. Palmer Utah Department of Public Safety, Utah Division of Emergency Management Robert Carey, Earthquake Program Manager Sheila Curtis, Operations Planner Federal Emergency Management Agency Doug Bausch, FEMA Region 8 Publication Editorial Review, Formatting, and Production (Utah Geological Survey) Steve D. Bowman, Ph.D., P.E., P.G., Geologic Hazards Program Manager Vicky Clarke, Publications Manager Acknowledgments (First Edition – 1996) Contractor Reaveley Engineers & Associates Inc. 675 East 500 South, Suite 400 Salt Lake City, Utah 84102 Utah Division of Comprehensive Emergency Management (CEM) Lorayne Frank, CEM Director Robert Carey, EPICENTER Manager Judy Watanabe, Natural Hazards Planner Brenda Edwards, Natural Hazards Office Technician Caryn Johnson, Natural Hazards Section Mikki Easton, Natural Hazards Section James Tingey, as he was instrumental in initiating this project Special thanks to: Lawrence D. Reaveley, Ph.D., S.E. Mark R. Harris, S.E. Debra A. Lewis, Structural Technician David J. Wagner, A.I.A. v The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings CONTENTS PREFACE........................................................................................................................................................................iii ACKNOWLEDGMENTS...............................................................................................................................................iv CHAPTER 1 Introduction. ..............................................................................................................................................1 CHAPTER 2 How to Use This Guide. ............................................................................................................................7 CHAPTER 3 Building Dynamics and Earthquake Forces. .............................................................................................9 CHAPTER 4 Typical Features of Unreinforced Masonry (URM) Construction. .........................................................13 CHAPTER 5 Typical Unreinforced Masonry Homes and Deficiencies.......................................................................17 Model A – Single Story, Double Wythe Brick with Basement..................................................................................19 Model B – Single Story, Double Wythe Brick with Basement and Attic..................................................................20 Model C – Two Story, Stucco-Covered Double Wythe Brick with Shelf Basement.................................................21 Model D – Two Story, Double Wythe Brick with Shelf Basement and Attic............................................................22 Model E – Single Story, Single Wythe Solid Brick with Full Basement. ..................................................................23 Model F – Single Story, Concrete/Cinder Block with Basement and Flat Roof.......................................................24 Model G – Seismic Mitigation of URM Structures...................................................................................................24 Special Features.........................................................................................................................................................25 CHAPTER 6 Seismic Mitigation of URM Structures..................................................................................................42 Individual Structural Repair Details..........................................................................................................................43 Structural bracing: Details 20–26a.......................................................................................................................44 Roof anchorage and strengthening: Details 30–43. ..............................................................................................51 Floor anchorage and strengthening: Details 50–57..............................................................................................76 Wall strengthening: Details 70–82. .......................................................................................................................84 Foundation anchorage and strengthening: Detail 90............................................................................................97 CHAPTER 7 Non-Structural Seismic Hazards: Anchorage and Bracing. ....................................................................99 Individual Non-Structural Sseismic Improvement Details......................................................................................100 Water heater bracing: Details 100–101. ..............................................................................................................101 Floor-mounted equipment: Detail 102. ...............................................................................................................103 Light-duty shelving: Detail 103. .........................................................................................................................103 Bookshelves against wall: Detail 104. ................................................................................................................104 Anchoring freestanding bookcase: Detail 105. ...................................................................................................105 Computers and accessories: Detail 106..............................................................................................................106 Wall-mounted televisions: Detail 107................................................................................................................107 Desktop/counter equipment restraint: Detail 108. ..............................................................................................108 Restraining brackets/straps: Detail 109..............................................................................................................109 Wall-mounted file cabinets: Detail 110.............................................................................................................. 110 Base-anchored file cabinets: Detail 111............................................................................................................. 111 Wall/base-anchored lateral file cabinets: Detail 112.......................................................................................... 112 Shelf-mounted items: Detail 113........................................................................................................................ 113 Fragile artwork restraints: Detail 114................................................................................................................. 114 Pendant light anchoring: Detail 115................................................................................................................... 115 APPENDICES.............................................................................................................................................................. 117 Appendix A – References and Supplemental Information. ...................................................................................... 117 Appendix B – Definitions........................................................................................................................................ 119 vi The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings FIGURES Figure 1. Braced exterior wall of a URM dwelling after an earthquake. ..........................................................................1 Figure 2. Cracks and failure due to earthquake................................................................................................................2 Figure 3. Unreinforced masonry collapse. ........................................................................................................................2 Figure 4. Interior URM wall collapse...............................................................................................................................3 Figure 5. URM wall (hollow clay units) collapse due to earthquake...............................................................................3 Figure 6. URM wall collapse from earthquake damage...................................................................................................4 Figure 7. Earthquake damage to URM wall and displacement of mechanical equipment on low roof...........................4 Figure 8. URM wall failure from an earthquake. ..............................................................................................................4 Figure 9. URM pier failure of a brick garage...................................................................................................................5 Figure 10. URM pier failure from an earthquake.............................................................................................................5 Figure 11. Chimney failure due to inadequate reinforcement..........................................................................................5 Figure 12. Chimney collapse............................................................................................................................................6 Figure 13. Displacement of wood-burning stove found in fireplace................................................................................6 Figure 14. Seismic improvement flowchart. .....................................................................................................................8 Figure 15. Epicenter map of mainshocks. .........................................................................................................................9 Figure 16. Isometric view of typical structure................................................................................................................10 Figure 17. Elements of a typical structure...................................................................................................................... 11 Figure 18. URM bearing wall.........................................................................................................................................13 Figure 19. Vertical section through URM walls.............................................................................................................13 Figure 20. In-plane failure..............................................................................................................................................14 Figure 21. Out-of-plane failure.......................................................................................................................................14 Figure 22. Wood post support and floor/roof support. ....................................................................................................14 Figure 23. Roof and floor diaphragms. ...........................................................................................................................14 Figure 24. Bearing wall and post and beam line. ............................................................................................................15 Figure 25. Parapet, chimney gable end wall, and corner window..................................................................................15 Figure 26. Representative model home types.................................................................................................................18 Figure 27. Model A front view. .......................................................................................................................................19 Figure 28. Model A rear view.........................................................................................................................................19 Figure 29. Model B front view.......................................................................................................................................20 Figure 30. Model B side view. ........................................................................................................................................20 Figure 31. 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