& 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
& 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
Common Earthquake Vulnerabilities Crawl Space House with Cripple Walls 5
Common Earthquake Vulnerabilities Crawl Space House with Cripple Walls 6
Common Earthquake Vulnerabilities Crawl Space House with Cripple Walls 7
Common Earthquake Vulnerabilities Slab-on-Grade House 8
Common Earthquake Vulnerabilities Slab-on-Grade House 9
Common Earthquake Vulnerabilities Slab-on-Grade House 10
Common Earthquake Vulnerabilities Perimeter Post-and-Pier House 11
Common Earthquake Vulnerabilities Hillside House Perime 12
Common Earthquake Vulnerabilities Perimeter Post-and-Pier House 13
Intended Users Home inspectors Home retrofit and remodel contractors Design professionals Homeowners Insurers Lenders Building officials Emergency planners Others involved in hazard mitigation 14
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
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
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
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-50-1 18
Part 1: Wood-Frame House Construction 19
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
Wood-Frame House Construction Crawl Space House with Cripple Walls 21
Wood-Frame House Construction Crawl Space House with Cripple Walls 22
Wood-Frame House Construction Basement or Foundation Wall House 23
Wood-Frame House Construction Basement or Foundation Stem Wall House 24
Wood-Frame House Construction Slab-on-Grade House 25
Wood-Frame House Construction Perimeter Post-and-Pier House Post Diagonal Brace Footing 26
Wood-Frame House Construction Perimeter Post-and-Pier House 27
Wood-Frame House Construction Perimeter Post-and-Pier House 28
PART 2: Dwelling Assessment 29
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
Seismic Performance Grade Intended Use: Single-family dwelling Primarily wood-frame construction Seismic Design Category C through E 31
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
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: 100 33
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
Structural Score Terminology Assessment Item A-1 Conditions a, b Penalty Points 35
Structural Score 36
Structural Score a. Continuous concrete and reinforced masonry exterior footings Continuous perimeter grade beams or tie-beams. 37
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
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
Structural Score 40
Structural Score 41
Structural Score 42
Structural Score 1 3 43
Structural Score 44
Structural Score 45
Structural Score Structural Score: 92.6 7.4 46
Structural Score 47
Structural Score Structural Score: 70.7 21.9 48
Structural Score Structural Score: 68.9 1.8 49
Structural Score Structural Score: 62.9 6.0 50
Structural Score Structural Score: 58.9 4.0 51
Regional Seismic Hazard Score 52
Regional Seismic Hazard Score http://earthquake.usgs.gov/designmaps/usapp 53
Regional Seismic Hazard Score 54
Regional Seismic Hazard Score http://earthquake.usgs.gov/designmaps/usapp http://earthquake.usgs.gov/designmaps/usapp 55
Regional Seismic Hazard Score 56
Regional Seismic Hazard Score 57
Regional Seismic Hazard Score 102 1.02 58
Regional Seismic Hazard Score 4 59
Regional Seismic Hazard Score 60
Regional Seismic Hazard Score http://myplan.calema.ca.gov 61
Regional Seismic Hazard Score 62
Regional Seismic Hazard Score 63
Regional Seismic Hazard Score 64
Regional Seismic Hazard Score 65
Regional Seismic Hazard Score 66
Regional Seismic Hazard Score http://myplan.calema.ca.gov 67
Regional Seismic Hazard Score 68
Regional Seismic Hazard Score 69
Regional Seismic Hazard Score 70
Regional Seismic Hazard Score 71
Regional Seismic Hazard Score 72
Regional Seismic Hazard Score 4 73
Regional Seismic Hazard Score 74
Regional Seismic Hazard Score http://myplan.calema.ca.gov 75
Regional Seismic Hazard Score http://geohazards.usgs.gov/qfaults/map.php 76
Regional Seismic Hazard Score 77
Regional Seismic Hazard Score 4 0 4 78
Seismic Performance Grade 7.4 21.9 1.8 6.0 4.0 41.1 58.9 4 79
Seismic Performance Grade 80
Seismic Performance Grade 7.4 21.9 1.8 6.0 4.0 41.1 58.9 4 C+ 81
Seismic Performance Grade 82
Basis for Seismic Performance Grades Letter Grades (Sec. 2.4.5) 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
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
Limits of the Methodology 85
Improving the Structural Score 86
Improving the Seismic Performance Grade 15.0 73.9 B 80.4 B+ 21.5 87
Improving the Seismic Performance Grade 88
PART 3: After the Assessment 89
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
Retrofit Regulation Mandatory Retrofit: May become mandatory triggered by: Alteration or addition to house Local retrofit ordinance 91
Retrofit Selection Voluntary Retrofit: Important to consider available guidance in: Selection of assessment items to retrofit Design of retrofit measures 92
Retrofit Selection Retrofit objective: Reduce damage Increase occupant safety NOT strengthen the entire house NOT avoid all damage 93
Retrofit Selection 94
Retrofit Selection FEMA P-50 Assessment Items FEMA P-50-1 Retrofit Guidance 95
Retrofit Design Guidance available: Not a single resource document to provide direction FEMA P-50-1 collects information on available methods and resources 96
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
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
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
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
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
QUESTIONS OR COMMENTS? 102