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

2 & Seismic Retrofit Guidelines for Detached, Single Family, Wood Frame Dwellings FEMA P 50 1 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 2

3 Intended Users Home inspectors Home retrofit and remodel contractors Design professionals Homeowners Insurers Lenders Building officials Emergency planners Others involved in hazard mitigation 5 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+ 6 3

4 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 7 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 8 4

5 Training Outline Part 1: Wood Frame House Construction Part 2: Assessment Using FEMA P 50 Part 3: Next Steps after the Assessment Using FEMA P Part 1: Wood Frame House Construction 10 5

6 Wood Frame House Construction Common house configurations: 1. Crawlspace w/ cripple wall 2. Basement & foundation wall 3. Slab on grade 4. Perimeter post & pier 11 Wood Frame House Construction Crawl Space House with Cripple Walls 12 6

7 Wood Frame House Construction Crawl Space House with Cripple Walls 13 Wood Frame House Construction Basement or Foundation Wall House 14 7

8 Wood Frame House Construction Basement or Foundation Wall House 15 Wood Frame House Construction Slab on Grade House 16 8

9 Wood Frame House Construction Slab on Grade House 17 Wood Frame House Construction Slab on Grade House 18 9

10 Wood Frame House Construction Perimeter Post and Pier House Post Diagonal Brace Footing 19 Wood Frame House Construction Perimeter Post and Pier House 20 10

11 Wood Frame House Construction Perimeter Post and Pier House 21 PART 2: Dwelling Assessment 22 11

12 Dwelling Assessment The inspector 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 23 Seismic Performance Grade Intended Use: Single family dwelling Primarily wood frame construction Seismic Design Category C through E 24 12

13 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 25 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:

14 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 27 Structural Score Terminology Assessment Item A 1 Conditions a, b Penalty Points 28 14

15 Structural Score 29 Structural Score a. Continuous concrete and reinforced masonry exterior footings Continuous perimeter grade beams or tie beams

16 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 31 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 32 16

17 Structural Score 33 Structural Score 34 17

18 Structural Score 35 Structural Score

19 Structural Score 37 Structural Score 38 19

20 Structural Score Structural Score: Structural Score 40 20

21 Structural Score Structural Score: Structural Score Structural Score:

22 Structural Score Structural Score: Structural Score Structural Score:

23 Regional Seismic Hazard Score 45 Regional Seismic Hazard Score

24 Regional Seismic Hazard Score 47 Regional Seismic Hazard Score

25 Regional Seismic Hazard Score 49 Regional Seismic Hazard Score 50 25

26 Regional Seismic Hazard Score Regional Seismic Hazard Score

27 Regional Seismic Hazard Score 53 Regional Seismic Hazard Score

28 Regional Seismic Hazard Score 55 Regional Seismic Hazard Score 56 28

29 Regional Seismic Hazard Score 57 Regional Seismic Hazard Score 58 29

30 Regional Seismic Hazard Score 59 Regional Seismic Hazard Score

31 Regional Seismic Hazard Score 61 Regional Seismic Hazard Score 62 31

32 Regional Seismic Hazard Score 63 Regional Seismic Hazard Score 64 32

33 Regional Seismic Hazard Score 65 Regional Seismic Hazard Score

34 Regional Seismic Hazard Score 67 Regional Seismic Hazard Score

35 Regional Seismic Hazard Score 69 Regional Seismic Hazard Score 70 35

36 Regional Seismic Hazard Score Seismic Performance Grade

37 Seismic Performance Grade 73 Seismic Performance Grade C

38 Seismic Performance Grade 75 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 76 38

39 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 77 Limits of the Methodology 78 39

40 Improving the Structural Score 79 Improving the Seismic Performance Grade B 80.4 B

41 Improving the Seismic Performance Grade 81 PART 3: After the Assessment 82 41

42 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 83 Retrofit Regulation Mandatory Retrofit: May become mandatory triggered by: Alteration or addition to house Local retrofit ordinance 84 42

43 Retrofit Selection Voluntary Retrofit: Important to consider available guidance in: Selection of assessment items to retrofit Design of retrofit measures 85 Retrofit Selection Retrofit objective: Reduce damage Increase occupant safety NOT strengthen the entire house NOT avoid all damage 86 43

44 Retrofit Selection 87 Retrofit Selection FEMA P 50 Assessment Items FEMA P 50 1 Retrofit Guidance 88 44

45 Retrofit Design Guidance available: Not a single resource document to provide direction FEMA P 50 1 collects information on available methods and resources 89 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 90 45

46 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 91 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 92 46

47 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 93 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 94 47

48 END QUESTIONS OR COMMENTS? 95 48