Motivation and Development of PBEE for
Existing and New Buildings
William T. Holmes
Structural Engineer
Rutherford & Chekene
Holmes
IRCC Workshop
October 18, 2006
1
Three areas of interest
• Retrofit of existing buildings
• Performance based codes (primarily new
buildings)
• Broad view
Holmes
IRCC Workshop
October 18, 2006
2
Performance Based Seismic Design:
Why the emphasis in the last decade?
•
The high cost of seismic retrofit, if done to
comply with the prescriptive code requirements
developed for design of new buildings,
- may be too high for economic feasibility
- may not provide the performance intended
• Economic losses were higher than expected by
owners due to both damage repair costs and
business interruption in the Loma Prieta, and
Northridge earthquakes (in this country).
Holmes
IRCC Workshop
October 18, 2006
3
FEMA 237: Issues Resolution
Predecessor to FEMA 273
• Phase 1 Project (1991-92)
Identified major issues and
recommended solutions
• On Performance Goals (Issue
11.2):
- Incrementalize and prioritize
strengthening activities to the
greatest extent possible.
Identify the performance
expectation of each increment.
- Specify requirements for Life
Safety, which would form the
core of the Guidelines
Holmes
IRCC Workshop
October 18, 2006
Issues Identification
and Resolution
4
Building Performance Levels from
FEMA 273
higher performance
1-A
1-B
3-C
5-E
Operational
Level
Immediate
Occupancy
Level
Damage
Control
Range
Code for new
buildings
Life Safety
Level
Collapse
Prevention
Level
Limited
Safety
Range
lower performance
Holmes
IRCC Workshop
October 18, 2006
5
Traditional Performance Based Code Process
Applied to Seismic Design
Performance Level
Performance Objective
Hazard
Characterization
Performance Requirements
Means of Verification
Serve as an
effective
“Alternate
Means”
For Equivalent
Performance
Prescriptive Criteria
Method
(Improve current code)
Holmes
Introduction of
Innovative Systems
IRCC Workshop
October 18, 2006
Alternate to
Prescriptions
For Superior
Performance
6
Conclusions/Opinions Regarding
Performance Based Codes
• Near term use of performance based design
concepts in codes will be:
- tuning the prescriptive provisions
- enabling development of “standards” for
acceptance of new systems
- Providing method to determine equivalence for
“alternate means”
- facilitating designs “over code” (voluntary)
• Performance based design (at least using the
detailed probabilistic methods, will not be the primary
code method for a long time--if ever.
Holmes
IRCC Workshop
October 18, 2006
7
A Broader View of
Earthquake Engineering
• Design of New Buildings
- Prescriptive “complete” method
- Simplified methods
• Individual Existing Buildings
- Evaluation
- Retrofit
- Determination of expected losses
• Groups of Buildings
- Risk analysis
- Economic portfolio analysis
- Regional loss studies
• Research and Reconnaissance
Holmes
IRCC Workshop
October 18, 2006
8
Integration of all Uses
Individual
Buildings:
•Evaluation
•Retrofit
Performance
Objective
Holmes
Building
Rating
Systems:
•Probable
Maximum Loss
•Other
Percentage or
Dollars
IRCC Workshop
October 18, 2006
Groups Of
Buildings:
•Portfolio
Analysis
•Regional Loss
Studies
•Mitigation
Studies
Casualties
Repair Costs
Downtime
9
Integration of all Uses
Groups Of
Building
Individual
Buildings:
Rating
Buildings:
Systems:•Portfolio
•Evaluation
•Probable Analysis
•Retrofit
Loss
Maximum •Regional
Loss
Studies
•Other
•Mitigation
Studies
Casualties
Percentage or
Repair Costs
Performance
Dollars
Downtime
Objective
Holmes
IRCC Workshop
October 18, 2006
10
Unified Performance System
Groups Of
Building
Buildings:
Evaluation
Rating
•Portfolio
Retrofit
Systems:
Analysis Rating
Building
•Probable
Portfolio
•Regional Loss
Maximum Loss
Analysis
Studies
•Other
Loss
Studies
•Mitigation
Mitigation
Studies
Studies
Casualties
Repair Costs
Downtime
Means of Verification
Holmes
IRCC Workshop
October 18, 2006
11
Interest and Demand from Stakeholders
Considering Broad Perspective
Uses
Stakeholders
Designers Building Owners Lenders Govern- Emer.
Officials
Insurers ment
Planners
New
Design
Evaluation
Retrofit
Building
Rating
Risk
Studies
Regional
Loss
Holmes
IRCC Workshop
October 18, 2006
12
Needed Extension of FEMA 356 Concepts
for Broader View
Elastic
Limit
Collapse
Displacement
IO
25%
0
0.0
0
Holmes
LS
0.0001
1
7
50%
CP
100%
0.001 0.01
30
.25
180
IRCC Workshop
October 18, 2006
Performance Level
$, % replacement
Casualty rate
Downtime, days
13
Uncertainty is Big Issue
Holmes
IRCC Workshop
October 18, 2006
14
Desirable Characteristics of the
Verification Method
Core of
Consider
“Performance Engine” uncertainty
Ground Motion
Extend over all
ground motions
P
Structural Response
M
Component and
global damage level
Losses:
Casualties
Cost of Repair
Loss of use
Average Annual
Loss
Cost Benefit
Analysis
Death, Dollars, and Downtime
Holmes
IRCC Workshop
October 18, 2006
15