Simplified Seismic Assessment & Seismic Retrofit Guidelines for Detached, Single-Family, Wood-Frame Dwellings FEMA P-50 & FEMA P-50-1

Transcription

1 & Seismic Retrofit Guidelines for Detached, Single-Family, Wood-Frame Dwellings FEMA P-50 & FEMA P-50-1

2 & Seismic Retrofit Guidelines for Detached, Single-Family, Wood-Frame Dwellings FEMA P-50

3 & Seismic Retrofit Guidelines for Detached, Single-Family, Wood-Frame Dwellings FEMA P-50-1

4 Intent: Provide a tool that communities and other entities can use to encourage the seismic retrofitting of residential structures, thereby reducing future earthquake losses 4

5 Common Earthquake Vulnerabilities Crawl Space House with Cripple Walls 5

6 Common Earthquake Vulnerabilities Crawl Space House with Cripple Walls 6

7 Common Earthquake Vulnerabilities Crawl Space House with Cripple Walls 7

8 Common Earthquake Vulnerabilities Slab-on-Grade House 8

9 Common Earthquake Vulnerabilities Slab-on-Grade House 9

10 Common Earthquake Vulnerabilities Slab-on-Grade House 10

11 Common Earthquake Vulnerabilities Perimeter Post-and-Pier House 11

12 Common Earthquake Vulnerabilities Hillside House Perime 12

13 Common Earthquake Vulnerabilities Perimeter Post-and-Pier House 13

14 Intended Users Home inspectors Home retrofit and remodel contractors Design professionals Homeowners Insurers Lenders Building officials Emergency planners Others involved in hazard mitigation 14

15 Training Objective: P-50 Seismic Assessment Introduce methodology to: Assign a Seismic Performance Grade Identify seismic retrofit opportunities & priorities Identify an improved Seismic Performance Grade with seismic retrofit C+ B+ 15

16 Seismic Performance Grade Seismic Performance Grade A through D- Conveys generally anticipated seismic performance Given structural characteristics & geographic location Relative to overall group of detached wood-framed single-family dwellings 16

17 Training Objective: P-50-1 Seismic Retrofit Provide a brief introduction to FEMA P-50-1 resources for: Selection of seismic retrofit measures to implement Design of seismic retrofit measures Reassessment of a dwelling 17

18 Webinar Outline Part 1: Wood-Frame House Construction Part 2: Assessment Using FEMA P-50 Part 3: Next Steps after the Assessment Using FEMA P

19 Part 1: Wood-Frame House Construction 19

20 Wood-Frame House Construction Common house configurations: 1. Crawlspace w/ cripple wall 2. Basement & foundation wall 3. Slab on grade 4. Perimeter post & pier 20

21 Wood-Frame House Construction Crawl Space House with Cripple Walls 21

22 Wood-Frame House Construction Crawl Space House with Cripple Walls 22

23 Wood-Frame House Construction Basement or Foundation Wall House 23

24 Wood-Frame House Construction Basement or Foundation Stem Wall House 24

25 Wood-Frame House Construction Slab-on-Grade House 25

26 Wood-Frame House Construction Perimeter Post-and-Pier House Post Diagonal Brace Footing 26

27 Wood-Frame House Construction Perimeter Post-and-Pier House 27

28 Wood-Frame House Construction Perimeter Post-and-Pier House 28

29 PART 2: Dwelling Assessment 29

30 Dwelling Assessment The assessor needs: One hour, approximately Knowledge of the basics of wood-frame construction, materials, construction techniques Helpful to have some knowledge of load path (how earthquake loads move through a structure) Equipment for inspecting attic, crawlspace FEMA P-50 assessment form 30

31 Seismic Performance Grade Intended Use: Single-family dwelling Primarily wood-frame construction Seismic Design Category C through E 31

32 Seismic Performance Grade Structural Score: A. Foundation B. Superstructure Framing and Configuration C. General Condition Assessment D. Nonstructural Elements, Age and Size E. Local Site Conditions Regional Seismic Hazard Score: F. Regional Seismic Hazard Score 32

33 Structural Score Structural Evaluation Areas: A. Foundation B. Superstructure Framing and Configuration C. General Condition Assessment D. Nonstructural Elements, Age and Size E. Local Site Conditions Structural Score:

34 Structural Score Terminology Assessment Items A-1 through E-6 are evaluated Penalty Points are assigned for each Assessment Item based on the applicable Condition (condition a, condition b, etc.) with the highest number of Penalty Points Summed Penalty Points are subtracted from 100 to give the Structural Score 34

35 Structural Score Terminology Assessment Item A-1 Conditions a, b Penalty Points 35

36 Structural Score 36

37 Structural Score a. Continuous concrete and reinforced masonry exterior footings Continuous perimeter grade beams or tie-beams. 37

38 Structural Score b. Continuous footings of other materials such as unreinforced brick or stone masonry. Discontinuous footings such as isolated post-and-pier systems, isolated drilled pier systems without tie-beams, and partially continuous perimeter footings 38

39 Structural Score b. Continuous footings of other materials such as unreinforced brick or stone masonry. Discontinuous footings such as isolated post-and-pier systems, isolated drilled pier systems without tie-beams, and partially continuous perimeter footings 39

40 Structural Score 40

41 Structural Score 41

42 Structural Score 42

43 Structural Score

44 Structural Score 44

45 Structural Score 45

46 Structural Score Structural Score:

47 Structural Score 47

48 Structural Score Structural Score:

49 Structural Score Structural Score:

50 Structural Score Structural Score:

51 Structural Score Structural Score:

52 Regional Seismic Hazard Score 52

53 Regional Seismic Hazard Score 53

54 Regional Seismic Hazard Score 54

55 Regional Seismic Hazard Score

56 Regional Seismic Hazard Score 56

57 Regional Seismic Hazard Score 57

58 Regional Seismic Hazard Score

59 Regional Seismic Hazard Score 4 59

60 Regional Seismic Hazard Score 60

61 Regional Seismic Hazard Score 61

62 Regional Seismic Hazard Score 62

63 Regional Seismic Hazard Score 63

64 Regional Seismic Hazard Score 64

65 Regional Seismic Hazard Score 65

66 Regional Seismic Hazard Score 66

67 Regional Seismic Hazard Score 67

68 Regional Seismic Hazard Score 68

69 Regional Seismic Hazard Score 69

70 Regional Seismic Hazard Score 70

71 Regional Seismic Hazard Score 71

72 Regional Seismic Hazard Score 72

73 Regional Seismic Hazard Score 4 73

74 Regional Seismic Hazard Score 74

75 Regional Seismic Hazard Score 75

76 Regional Seismic Hazard Score 76

77 Regional Seismic Hazard Score 77

78 Regional Seismic Hazard Score

79 Seismic Performance Grade

80 Seismic Performance Grade 80

81 Seismic Performance Grade C+ 81

82 Seismic Performance Grade 82

83 Basis for Seismic Performance Grades Letter Grades (Sec ) Expert Opinion Los Angeles pilot study of 400 dwellings Damage Ranges Percent of replacement cost of house Annual probability of exceedance of 1/500 Reasonable approximation of single event for which owner will have to repair damage Based on 2012 EQECAT study using modifiers developed for CEA, modeling 7600 combinations of dwelling configuration and seismic design category, and covering a range of seismic events deemed credible by USGS 83

84 Limits of the Methodology (Sec. 2.5) Performance for an assigned grade could vary widely due to limits of assessment Dwelling construction and resulting earthquake response is inherently variable Limited portions of the structure are visible without removing finish materials Variability is inherent in seismic hazard Owner could choose to perform a more detailed assessment to increase level of knowledge 84

85 Limits of the Methodology 85

86 Improving the Structural Score 86

87 Improving the Seismic Performance Grade B 80.4 B

88 Improving the Seismic Performance Grade 88

89 PART 3: After the Assessment 89

90 Retrofit Regulation Voluntary Retrofit: Owner is generally free to Choose to implement seismic retrofits Select which assessment items to retrofit Provided the retrofit does not make the house more vulnerable to earthquake damage 90

91 Retrofit Regulation Mandatory Retrofit: May become mandatory triggered by: Alteration or addition to house Local retrofit ordinance 91

92 Retrofit Selection Voluntary Retrofit: Important to consider available guidance in: Selection of assessment items to retrofit Design of retrofit measures 92

93 Retrofit Selection Retrofit objective: Reduce damage Increase occupant safety NOT strengthen the entire house NOT avoid all damage 93

94 Retrofit Selection 94

95 Retrofit Selection FEMA P-50 Assessment Items FEMA P-50-1 Retrofit Guidance 95

96 Retrofit Design Guidance available: Not a single resource document to provide direction FEMA P-50-1 collects information on available methods and resources 96

97 Retrofit Design Prescriptive: Construction requirements are prescribed in detail in text, tables, and/or figures Generally does not require involvement of a engineer/ architect can be implemented directly by contractor Limits exist on the type and configuration of the building to be retrofit Engineered: Construction requirements are calculated for particular building based on specific earthquake loading Requires involvement of engineer/ architect in addition to contractor, with greater time and expense No limits on type an configuration of building 97

98 Retrofit Methods Method 1: Prescriptive International Existing Building Code (IEBC) Chapter A3 cripple wall bracing and anchorage to foundation Method 2: Prescriptive retrofit method for nonstructural building elements Method 3: Prescriptive retrofit method in accordance with International Residential Code (IRC) requirements for new construction Method 4: Engineered retrofit method 98

99 Reassessment of the Seismic Performance Grade Fundamental to the FEMA P-50 assessment process is the concept that dwellings can be reassessed. This might be done to: Revise the Seismic Performance Grade following retrofit Better assess items addressed in the assessment form as a detailed rather than simplified assessment 99

100 Reassessment of the Seismic Performance Grade The qualified design professional would be: An engineer or architect experienced in structural engineering can re-evaluate penalty points assigned towards the Structural Score A geotechnical engineer can re-evaluate the assigned Regional Seismic Hazard Score 100

101 Implementation of an Assessment Program The benefits of reduced economic losses following a major to moderate earthquake extend to the homeowner, but also to many others beyond. Following are some of the persons and organizations that serve to benefit and therefore should consider establishment of plans to implement a program of assessment and retrofit: Homeowner Lender Insurer Local government 101

102 QUESTIONS OR COMMENTS? 102