RESIDENTIAL SEISMIC RETROFITS

Transcription

1 RESIDENTIAL Barry H. Welliver Structural Engineer BHW Engineers SEAU 6th Annual Education Conference Davis Conference Center - Layton, Utah February 21st, 2018 TOPICS Introduction to Seismic Retrofits for Residential Buildings Building Codes and Programs (Legal & Ethical Responsibilities) Beyond the Building Codes (Sound Advice / State of the Art) Client Relations (Figuring Out the Scope of Work) Unreinforced Masonry Residential Buildings The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings URM Rehabilitation Example Other Residential Buildings Salt Lake City s Fix the Bricks Program Questions? (and maybe some answers)

2 FOR RESIDENTIAL BUILDINGS BUILDING CODES AND PROGRAMS International Existing Building Code (IEBC) Replaces Chapter 34 (Existing Buildings) in the 2015 IBC. The provisions of the International Existing Building Code shall apply to matters governing the repair, alteration, change of occupancy, addition to and relocation of existing buildings. Mandated, Triggered and Voluntary requirements: Mandatory generally targeting specific building types or features. (Active programs) Triggered requirements are generally invoked when altering the vertical or lateral capacity of the existing building. (Passive Programs) Voluntary rehabilitation is when owner chooses to upgrade vertical or lateral capacities of the building. FOR RESIDENTIAL BUILDINGS BEYOND BUILDING CODES Seismic Evaluation and Retrofit of Existing Buildings ASCE/SEI Stated of the art - deficiency-based procedures Techniques for the Seismic Rehabilitation of Existing Buildings FEMA 547/2006 Edition Chapter 21 - Building Type URM: Unreinforced Masonry Bearing Walls Engineering Guideline for Incremental Seismic Rehabilitation FEMA 420 / December 2008 Chapter 4 - Engineering Resources for Seismic Evaluation and Rehabilitation Section Code Rationalizations for Incremental Seismic Rehabilitation Building codes allow existing buildings to remain in use without having to fully comply with the requirements for new buildings. This is generally referred to as nonconforming rights

3 FOR RESIDENTIAL BUILDINGS CLIENT RELATIONS Most clients don t know what they need to know. Some know they probably need to do something. Others are incorporating seismic into a remodel or addition. You are (usually) their best source for the technical stuff Giving advice is a dance don t get into the weeds (too soon) Admit that you re probably not the best source for costs. But don t punt entirely. Think about the larger picture ask questions about what they are trying to achieve. But are you their only source of information and advice? Recommend consultants when appropriate Geologist, architect, soils engineers, etc. Contractors may be hard to find Look beyond the anxiety. UNREINFORCED MASONRY BUILDINGS

4 THE UTAH GUIDE FOR SEISMIC IMPROVEMENTS UNREINFORCED MASONRY DWELLINGS THE UTAH GUIDE FOR THE SEISMIC IMPROVEMENT OF UNREINFORCED MASONRY DWELLINGS THE UTAH GUIDE FOR SEISMIC IMPROVEMENTS UNREINFORCED MASONRY DWELLINGS Utah Seismic Safety Commission Existing Buildings Committee Second Edition 2016

5 TABLE OF CONTENTS ACKNOWLEDGMENTS... CHAPTER 1 Introduction... CHAPTER 2 How to Use This Guide... CHAPTER 3 Building Dynamics and Earthquake Forces... CHAPTER 4 Typical Features of Unreinforced Masonry (URM) Construction... CHAPTER 5 Typical Unreinforced Masonry Homes and Deficiencies... Model A Single Story, Double Wythe Brick with Basement... Model B Single Story, Double Wythe Brick with Basement and Attic... Model C Two Story, Stucco-Covered Double Wythe Brick with Shelf Basement... Model D Two Story, Double Wythe Brick with Shelf Basement and Attic... Model E Single Story, Single Wythe Solid Brick with Full Basement... Model F Single Story, Concrete/Cinder Block with Basement and Flat Roof... Model G Seismic Mitigation of URM Structures... Special Features... CHAPTER 6 Seismic Mitigation of URM Structures... Individual Structural Repair Details... Structural bracing: Details 20 26a... Roof anchorage and strengthening: Details Floor anchorage and strengthening: Details Wall strengthening: Details Foundation anchorage and strengthening: Detail CHAPTER 7 Non-Structural Seismic Hazards: Anchorage and Bracing CHAPTER 2 HOW TO USE THIS GUIDE Begin Seismic Improvement Review Select Model Dwelling that Best Describes Subject Structure Identify Other Model Dwellings Which Have Elements Similar To Subject Structure Estimate the Cost of Corrective Measures Review Alternative Ways to Implement Corrective Measures and Select Most Appropriate Approach Compile List of Deficiencies and Corrective Measure for Subject Dwelling Is Cost Acceptable? NO YES Phase the Project or Select Corrective Measures that are Affordable Start Construction Process Figure 14. Dwelling seismic improvement flowchart.

6 CHAPTER 4 TYPICAL FEATURES OF UNREINFORCED MASONRY The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwelli Figure 20. In-plane failure. Figure 22. Wood post support and floor/roof support. Figure 18. URM bearing wall. Figure 21. Out-of-plane failure. Figure 23. Example of roof and floor diaphragms. Figure 19. Vertical section through URM walls. CHAPTER 4 TYPICAL FEATURES OF UNREINFORCED MASONRY 14 The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings Figure 20. In-plane failure. Figure 22. Wood post support and floor/roof support. The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings 15 Special Features Most URM dwellings contain the basic structural elements described in this guide, however there are special features that may not be present in all URM dwellings or may vary from one dwelling to another. The special features covered in this guide include URM parapets, masonry gable end walls, chimneys, and corner windows (figure 25). There are other special features found on URM dwellings, however these are the most common. A description of each of these items, their deficiencies, and Figure references 21. Out-of-plane to the appropriate failure. corrective measures are included at the end of Chapter 5. 21). The floor joists usually pocket into the masonry and the roof joists normally bear on top of wall. In both cases, there may or may not be a wood plate to which these joists are nailed. Failure of these connections can cause the joists to slide off their bearing support, resulting in full or partial collapse of a floor or roof. Another common failure in multiple wythe (or vertical layer) construction where one or more of the outer wythes of brick may fall away from the rest of the wall, as they are not connected together. Masonry Piers (Columns) Figure Figure Bearing Example wall of and roof post and and floor beam diaphragms. line. Floor and Roof Diaphragms The diaphragm is the structural element that consists of sheathing fastened to the underlying joists, creating a flat floor/roof or a sloping roof, which distributes forces throughout a particular level of the dwelling (figure 23). Horizontal forces generated in the masonry walls are transferred to the diaphragms. The diaphragms in URM construction generally fail due to the large forces generated from the weight of the surrounding masonry and/or the poor connections tying the diaphragms and walls together. Masonry piers can be located within the dwelling under the Interior Bearing Walls and/or main beam line that Figure supports 25. the Examples first floor of or a parapet, at the exterior chimney gable end wall, and Post corner and window. Beam Lines to support the roof over a porch (figure 22). In both cases, the pier either continues to the floor or roof, or supports a The interior-bearing element may be an URM wall, a wood wood post that then continues to the floor or roof. These stud wall, a post and beam line, or any combination (figure piers are subject to the same type of failure as the masonry 24). This intermediate support is required because the floor foundation wall. Taller piers will have tendency to topple and roof joists generally cannot span between exterior or buckle during an earthquake. walls. These elements will normally fail from inadequate connections or lack of any connections to each other.

7 CHAPTER 5 TYPICAL URM HOMES AND DEFICIENCIES Model A Model B Model C Model D CHAPTER 5 TYPICAL URM HOMES AND DEFICIENCIES Model E Model F Figure 26. Representative model dwelling types. Model G

8 CHAPTER 5 TYPICAL URM HOMES AND DEFICIENCIES Table 1. Typical seismic improvement details for model dwelling types A to G for various seismic deficiencies. Seismic Deficiencies (In order of highest priority to lowest priority) Strengthening and Bracing of Special Features Roof to URM Wall Anchorage Floor to URM Wall and Foundation Wall Anchorage URM Wall Strengthening Roof Diaphragm Strengthening Floor Diaphragm Strengthening Strengthening of Major Interior Bearing Elements Foundation Wall Strengthening Non-Structural Bracing and Anchorage Model Dwelling Types A B C D E F G Details Details 30 and and 36 Details 20, 22, 24, 25, and 26 Details 32 and 37 Details 51, 53, and 54 Details 50, 51, 53, 54, and 56 Details 40 and 43 Detail 57 Detail 90 Details 33 and 38 Detail 34 Details 32 and 36 Details 52 and 55 Detail 51 Details 51 and 54 Details 70 and 74 Details 75 and 76 Details 77 and 82 For bracing and anchorage of non-structural items, including water heaters, furnishings, cabinets, equipment, etc., see details 100 and higher. MODEL BUILDING A -SINGLE STORY DOUBLE WYTHE W/ BASEMENT The seismic deficiencies observed in Model A are: although not illustrated in these exterior wall details. 1. The lack of anchorage of the roof to the URM exterior walls. There may or may not be a wood plate on top of the typical URM wall which this home did not have. 2. The lack of anchorage of the floor to the URM exterior and concrete foundation walls. 3. The chimneys are not braced. 4. The lack of continuous sheathing makes the roof diaphragm weak. There are 1 x 8 inch wood boards spaced at approximately 12 inches on center. 5. The masonry bearing walls are unreinforced. 6. The tall masonry porch piers are not braced or adequately attached to the porch roof. 7. The interior wood stud bearing walls are not anchored to the floor or roof. 8. The water heater is not braced and utility connections are rigid pipe.

9 28 The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings MODEL BUILDING A -SINGLE STORY DOUBLE WYTHE W/ BASEMENT Model A: Details 1 2 Single story, double wythe brick with basement The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings 77 The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings MODEL BUILDING C -TWO STORY DOUBLE WYTHE W/ SHELF BASEMENT for the Seismic Improvement of Unreinforced Masonry Dwellings 21 Model C Two Story, Stucco-Covered Double Wythe Brick with Shelf Basement Model C was built in the 1900s, and is a two-story home with a concrete shelf basement (figures 31 and 32). The construction consists of double wythe URM exterior walls covered with stucco, masonry/rock foundation walls supporting a wood floor and roof/ceiling joists around the exterior. A wood beam on masonry piers or wood posts supports the floor, while a wood stud wall supports the roof. It has two exterior chimneys and several small roof areas built into the dwelling. Model C o Story, Stucco-Covered ble Wythe Brick with Shelf Basement C was built in the 1900s, and is tory home with a concrete shelf t (figures 31 and 32). The construcsists of double wythe URM exterior overed with stucco, masonry/rock on walls supporting a wood floor f/ceiling joists around the exterior. beam on masonry piers or wood pports the floor, while a wood stud ports the roof. It has two exterior s and several small roof areas built dwelling. mic deficiencies observed in Model e lack of anchorage of the roof to URM exterior walls. There may or y not be a wood plate on top of the ical URM wall which this home did t have. The small areas at the front trances are also not anchored. e lack of anchorage of the floor to URM exterior and concrete foundan walls. e chimneys are not braced. e lack of continuous sheathing makes the f diaphragm weak. There are 1 x 8 inch od boards spaced at approximately 12 hes on center. Figure 31. Model C front view. The seismic deficiencies observed in Model C are: 1. The lack of anchorage of the roof to the URM exterior walls. There may or may not be a wood plate on top of the typical URM wall which this home did not have. The small areas at the front entrances are also not anchored. 2. The lack of anchorage of the floor to the URM exterior and concrete foundation walls. 3. The chimneys are not braced. 4. The lack of continuous sheathing makes the roof diaphragm weak. There are 1 x 8 inch wood boards spaced at approximately 12 inches on center. 5. The masonry/rock foundation walls have deteriorated. 6. The masonry bearing walls are unreinforced. 7. The interior wood stud bearing walls are not anchored to the floor or roof. 8. The water heater is not braced and utility connections are rigid pipe. Details 5 and 6 show two different existing exterior walls sections for Model C. Reference circles have been superimposed onto the details showing the area of the wall where seismic deficiencies normally occur. The details for improvements to strengthen Figure 31. Model C front vie

10 floor, while a wood stud roof. It has two exterior eral small roof areas built encies observed in Model anchorage of the roof to erior walls. There may or wood plate on top of the wall which this home did e small areas at the front also not anchored. Model C: Details 5 6 Two story, stucco-covered, double wythe brick with shelf basement and attic MODEL BUILDING C -TWO STORY DOUBLE WYTHE W/ SHELF BASEMENT Figure 31. Model C front view. anchorage of the floor to erior and concrete foundas are not braced. continuous sheathing makes the gm weak. There are 1 x 8 inch s spaced at approximately 12 ter. y/rock foundation walls have bearing walls are unreinforced. wood stud bearing walls are not he floor or roof. eater is not braced and utility re rigid pipe. w two different existing exterior Model C. Reference circles have d onto the details showing the ere seismic deficiencies normally for improvements to strengthen are found in Chapter 6. Table 1 details in Chapters 6 and 7 also improvements, although not exterior wall details. Figure 32. Model C rear view. 76 The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings Floor anchorage and strengthening: Details The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings MODEL BUILDING C -TWO STORY DOUBLE 55 WYTHE W/ SHELF BASEMENT

11 MODEL BUILDING E - SINGLE STORY SINGLE WYTHE W/ FULL BASEMENT The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings 23 Figure 35. Model E front view. Figure 35. Model E front view. Model E Single Story, Single Wythe Solid Brick with Full Basement Model E was built in approximately 1966, and is singlestory home with a full basement and a low slope roof (figures 35 and 36). The construction consists of single wythe URM exterior walls and concrete foundation walls supporting wood floor joists and roof trusses around the exterior with wood stud bearing walls supporting the interior. The roof structure extends over the carport and changes from trusses to sloped joists supported by wood beams at the ridge and ends. The end beams are carried by steel or wood columns. 5. The interior wood stud bearing walls are not anchored to the floor or roof. 6. The water heater is not braced and utility connections are rigid pipe. Model E: Details 9 10 Single story, single wythe, solid brick with full basement MODEL BUILDING E - SINGLE STORY SINGLE WYTHE W/ FULL BASEMENT The seismic deficiencies observed in Model E are: 1. The lack of anchorage of the roof to the URM exterior walls. 2. The lack of anchorage of the floor to the URM exterior and concrete foundation walls. 3. The masonry bearing walls are unreinforced. 4. The beams and columns for the carport are not anchored or braced to the roof or to the masonry walls of the dwelling. 6. The water heater is not braced and utility connections are rigid pipe. Details 9 and 10 show two different existing exterior wall sections for Model E. Reference circles have been superimposed into these details showing the area of the wall where seismic deficiencies normally occur. The details for improvements to strengthen these deficiencies are found in Chapter 6. Table 1 and the additional details in Chapters 6 and 7 also recommend other improvements, although not illustrated in these exterior wall details. Figure 36. Model E rear view.

12 The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings 59 MODEL BUILDING E - SINGLE STORY SINGLE WYTHE W/ FULL BASEMENT 48 The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings 46 The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings CHIMNEYS, GABLES & FOUNDATIONS

13 CHIMNEYS, GABLES & FOUNDATIONS The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings 47 The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings The Utah Guide for the Seismic Improvement of Unreinforced Masonry Dwellings Foundation anchorage and strengthening: Detail 90 CHIMNEYS, GABLES & FOUNDATIONS

14 URM RETROFIT Designer Buona Vita Design Group 9460 South Union Square #231 Sandy, Utah PROJECT # 08UT16.0 DATE : 10/24/2008 SUBMITTAL : PLANCHECK FRONT ELEVATION SCALE: 1/4" = 1'-0" FRONT ELEVATION SCALE: 1/4" = 1'-0" A RESIDENTIAL REMODEL FOR KELLY HARWARD SCHEMATIC ELEVATIONS FORT STREET DRAPER, UTAH LEFT ELEVATION SCALE: 1/8" = 1'-0" BACK ELEVATION SCALE: 1/8" = 1'-0" RIGHT ELEVATION SCALE: 1/8" = 1'-0" A3 URM RETROFIT PROJECT # 08UT16.0 DATE : 10/24/2008 SUBMITTAL : PLANCHECK A RESIDENTIAL REMODEL FOR KELLY HARWARD FORT STREET DRAPER, UTAH Structural Engineer BHW Engineers, L.L.C. 132 East South Suite 210 Draper, Utah T F Designer Buona Vita Design Group 9460 South Union Square #231 Sandy, Utah FOOTING AND FOUNDATION PLAN SCALE: 1/4" = 1'-0" NOTES: LOWER FLOOR FRAMING PLAN STRUCTURAL FOUNDATION PLAN & NOTES SCALE: 1/4" = 1'-0" NOTES: 1. ALL WORK SHALL COMPLY WITH THE REQUIREMENTS OF THE 2006 INTERNATIONAL BUILDING CODE AS ADOPTED BY SALT LAKE CITY 2. VERIFY ALL DIMENSIONS AND CONSTRUCTION WITH ARCHITECTURAL DRAWINGS AND IN THE FIELD - REPORT ANY DISCREPANCIES TO ARCHITECT AND ENGINEER IN THE FIELD PRIOR TO PLACING ANY REINFORCING STEEL 3. ALL NEW FOOTINGS TO REST IN FIRM, UNDISTURBED NATURAL SOILS. 4. REFER TO SHEET S5 FOR TYPICAL STRUCTURAL NOTES AND DETAILS 1. ALL WORK SHALL COMPLY WITH THE REQUIREMENTS OF THE 2006 INTERNATIONAL BUILDING CODE AS ADOPTED BY CITY OF DRAPER 2. VERIFY ALL DIMENSIONS AND CONSTRUCTION WITH ARCHITECTURAL DRAWINGS AND IN THE FIELD - REPORT ANY DISCREPANCIES TO ARCHITECT AND ENGINEER IN THE FIELD PRIOR TO PLACING ANY REINFORCING STEEL 3. ALL EXTERIOR WALLS TO BE SHEATHED WITH 1 2" PLYWOOD SHEATHING SCHEDULE A NAILING, UNLESS NOTED OTHERWISE. 4. REFER TO SHEET S5 FOR TYPICAL STRUCTURAL NOTES AND DETAILS S1

15 URM RETROFIT URM RETROFIT A RESIDENTIAL REMODEL FOR KELLY HARWARD FORT STREET DRAPER, UTAH Structural Engineer BHW Engineers, L.L.C. 132 East South Suite 210 Draper, Utah T F PROJECT # Designer 08UT16.0 Buona Vita Design Group DATE : 9460 South Union Square #231 Sandy, Utah /24/ SUBMITTAL : PLANCHECK PLAN LOWER FLOOR FRAMING PLAN STRUCTURAL FOUNDATION LAN & NOTES

16 URM RETROFIT UPPER FLOOR FRAMING SCALE: 1/4" = 1'-0" NOTES: 1. ALL WORK SHALL COMPLY WITH THE REQUIREMENTS OF THE 2006 INTERNATIONAL BUILDING CODE AS ADOPTED BY CITY OF DRAPER 2. VERIFY ALL DIMENSIONS AND CONSTRUCTION WITH ARCHITECTURAL DRAWINGS AND IN THE FIELD - REPORT ANY DISCREPANCIES TO ARCHITECT AND ENGINEER IN THE FIELD PRIOR TO PLACING ANY REINFORCING STEEL 3. ALL EXTERIOR WALLS TO BE SHEATHED WITH 1 2" PLYWOOD SHEATHING SCHEDULE A NAILING, UNLESS NOTED OTHERWISE. 4. REFER TO SHEET S5 FOR TYPICAL STRUCTURAL NOTES AND DETAILS 5. FLOOR SHEATHING TO BE 3 4" T&G PLYWOOD WITH SCHEDULE A NAILING U.N.O. ROOF FRAMING PLAN SCALE: 1/4" = 1'-0" NOTES: 1. ALL WORK SHALL COMPLY WITH THE REQUIREMENTS OF THE 2006 INTERNATIONAL BUILDING CODE AS ADOPTED BY CITY OF DRAPER 2. VERIFY ALL DIMENSIONS AND CONSTRUCTION WITH ARCHITECTURAL DRAWINGS AND IN THE FIELD - REPORT ANY DISCREPANCIES TO ARCHITECT AND ENGINEER IN THE FIELD PRIOR TO PLACING ANY REINFORCING STEEL 3. ALL EXTERIOR WALLS TO BE SHEATHED WITH 1 2" PLYWOOD SHEATHING SCHEDULE A NAILING, UNLESS NOTED OTHERWISE. 4. REFER TO SHEET S5 FOR TYPICAL STRUCTURAL NOTES AND DETAILS 5. ROOF SHEATHING TO BE 5 8" PLYWOOD WITH SCHEDULE A NAILING U.N.O. URM RETROFIT UPPER FLOOR FRAMING SCALE: 1/4" = 1'-0" ROOF FRAMING PLA SCALE: 1/4" = 1'-0"

17 SCALE: 1" = 1'-0" SCALE: 1" = 1'-0" S3 SCALE: 1" = 1'-0" DRAPER, UTAH FORT STREET SUBMITTAL : PLANCHECK DATE : 10/24/2008 PROJECT # 08UT16.0 URM RETROFIT Buona Vita Design Group 9460 South Union Square #231 Sandy, Utah Designer DRAPER, UTAH FORT STREET A RESIDENTIAL REMODEL FOR KELLY HARWARD BHW Engineers L.L.C South 132 East Suite 210 Draper, Utah STRUCTURAL ENGINEER Buona Vita Design Group 9460 South Union Square #231 Sandy, Utah Designer SUBMITTAL : PLANCHECK DATE : 10/24/2008 PROJECT # 08UT16.0 BHW Engineers L.L.C South 132 East Suite 210 Draper, Utah STRUCTURAL ENGINEER A RESIDENTIAL REMODEL FOR KELLY HARWARD STRUCTURAL DETAILS STRUCTURAL DETAILS URM RETROFIT SCALE: 1" = 1'-0" S3

18 URM RETROFIT STRUCTURAL DETAILS SCALE: 1" = 1'-0" URM RETROFIT

19 URM RETROFIT OTHER RESIDENTIAL BUILDINGS

20 SALT LAKE CITY S FIX THE BRICKS PROGRAM

21 SALT LAKE CITY S FIX THE BRICKS PROGRAM Thank You! Questions?