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Implications of Recent FEMA P-58 Methodology Advancements
for Resilient BRBF Design
Presented by: Curt B. Haselton, PhD, PEJohn F. O’Connell Endowed Professor @ CSU, Chico
Co-Founder and CEO @ Haselton Baker Risk Group (SP3)
Work by: The Full SP3 TeamEdward Almeter (project lead), Jack Baker, Katie Wade,, D. Jared DeBock,
Shaunt Kojabashian, Mike McGlone, Tracy Rice, and Dustin Cook
SP3 | where research meets practicewww.hbrisk.com
NASCC Steel Conference | April 5, 2019
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§ Motivation – Current performance and the push for resilient design
§ The FEMA P-58 Methodology for assessing resilience:ü Overviewü Method enhancement for BRBFs
§ Updated resilience predictions for BRBFs§ Resilient design of BRBFs§ Summary and Q&A
Presentation Outline
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§ Motivation – Current performance and the push for resilient design
§ The FEMA P-58 Methodology for assessing resilience:ü Overviewü Method enhancement for BRBFs
§ Updated resilience predictions for BRBFs§ Resilient design of BRBFs§ Summary and Q&A
Presentation Outline
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Code Design (ASCE7, etc.)§ Safety Goal – Yes (divides for demands by R and results in a
“safe but disposal” building)
“Performance”-Based Design (ASCE 41, SF AB 083, etc.)§ Safety Goal – Yes§ Also enhanced modeling and design scrutiny
“Resiliency”-Based Design (and Risk Assessment)§ Safety Goal – Yes§ Repair Time Goal – Yes§ Repair Cost Goal - Yes§ Also enhanced modeling and design scrutiny
Current Performance and Push for Resilient Design
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Current Performance and Push for Resilient Design
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§ Safety: Expected to be safe (per 1989 and 1994 experience), but this was not assessed in this study.
§ Losses: 5-25% mean loss for design event and 10-80% loss for rare event (huge range!).
§ Downtime: 6-12 months for design event and up to 2 years for rare event (substantial predicted downtimes!).
§ Why?: High values and huge ranges of performance because resiliency (losses and downtime) are simply not constrained in our code design process.
Hence, we refer to code-compliant buildings as safe but
disposable for a rare event!
Current Performance and Push for Resilient Design
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How can we do better?§ Design buildings not only to be safe, but also to limited
downtime, and possibly also to limit repair cost.§ Two options:
a) Do direct resilient design using targets for downtime/losses and using FEMA P-58 analysis method.
b) Do indirect resilient design using modified building code requirements (e.g. Risk Category IV), but such requirement have not yet been developed (in process).
c) a
§ A§ a
Current Performance and Push for Resilient Design
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Current pushes for resilient design at all levels:§ California Assembly Bill 393 – “functional recovery” code
provisions for California § NEHRP Reauthorization – Congress tasked NIST/FEMA with
recommendations for design for functional recovery§ Cities like San Francisco – considering enhanced design
requirements for tall buildings (to consider functionality)
Current Performance and Push for Resilient Design
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§ Motivation – Current performance and the push for resilient design
§ The FEMA P-58 Methodology for assessing resilience:ü Overviewü Method enhancement for BRBFs
§ Updated resilience predictions for BRBFs§ Resilient design of BRBFs§ Summary and Q&A
Presentation Outline
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§ FEMA P-58 is a probabilistic performance prediction methodology (15 year, $16M+ invested, ~100+ on the team)
§ FEMA P-58 is tailored for building-specific analysis (in contrast to most risk assessment methods)
§ FEMA P-58 output results:• Repair costs• Repair time• Safety: Fat & Injury
FEMA P-58: Overview
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Site Hazard Structural Responses
Structural Components &
Fragilities
Nonstructural Components &
Fragilities
Building-Specific Vulnerability
Curves
Full distributions of losses and repair
times, and expected annual values.
FEMA P-58 Monte Carlo Analysis
ENGINE
FEMA P-58: Detailed Steps of Method
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FEMA P-58: Ground Motions
§ Step 1: Define ground motion hazard (with soil)• Option #1: SP3 can provide curve (given an address)
• Option #2: User-specified curve
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FEMA P-58: Structural Response
§ Step 2: Predict “engineering demand parameters”
• Story drift ratio at each story• Peak floor acceleration at each
floor• For wall buildings, also wall
rotations and coupling beam rotations
Option #1: Response-history structural analysis
Option #2: Statistically calibrated predictive equations (**and we will need to extend these for BRBFs**)
EQ: 11122, Sacomp(T=1sec): 1.02g
Deierlein, Haselton, Liel (Stanford University)
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FEMA P-58: Component Damage
§ Step 3: Quantify component damageFirst, establish what components are in the building. Types and quantities of can be specified or estimated from building size and occupancy type
Windows Piping
Partitions Structural components
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We end up with a list of component types, quantities and locations
FEMA P-58: Component Damage
§ Step 3: Quantify component damage
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Each component type has a “fragility function” that specifies the probability that a structural demand causes damage (**and we will need these for CoreBrace BRBFs**)
FEMA P-58: Component Damage
§ Step 3: Quantify component damage
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FEMA P-58: Consequences of Damage
Fragility functions have been calibrated for hundreds of components from test data, and repair cost and labor has been developed by cost estimators.
Cost per 100 ft. Labor per 100 ft.Cracked wallboard $2,730 24 person-hours
Crushed gypsum wall $5,190 45 person-hours
Buckled studs $31,100 273 person-hoursThese are median values—each also has uncertainty
§ Step 4: Quantify consequences of the component damage (component repair costs, repair times, etc.).
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FEMA P-58: Building-Level Consequences
Repair costs are the sum of component repair costs (considering volume efficiencies)
Recovery time is aggregated from component damage, but is more complex (mobilization, staffing, construction sequencing, …)
Windows $26,892Partitions $43,964
Piping $5,456
Structural Components
$77,920
… …
Sum = $253,968
§ Step 5: Aggregate to building-level consequences
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FEMA P-58: Monte Carlo Simulations
For a given building and ground shaking intensity, repeat the following steps 2,000-10,000 times!
1. Simulate each structural response parameter2. Simulate damage to each component3. Simulate repair costs and repair time for each component4. Aggregate to compute total repair cost and recovery time
We can then look at the mean cost, 90th percentile, etc.
§ Step 5: Aggregate to building-level consequences
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FEMA P-58: Summary
§ Step 1: Site Hazard• Soil and hazard curve
• Ground motions (if needed)
§ Step 2: Structural Responses• Option #1: Structural analysis• Option #2: Predictive equations
§ Step 3: Damage Prediction• Contents • Fragility curves
§ Step 4: Loss Estimation (loss curves & other consequences)
Step 5: Aggregate to building-level consequences
Thousands of Monte Carlo simulations
The simulations provide detailed statistical
information on building performance.
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8%
70%
16%
0% 3% 3% 0% 0%0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
StructuralComponents
Partitions InteriorFinishes
Cladding Plumbing andHVAC
OtherComponents
Collapse Residual Drift
Loss Contributions by Component Type for a 50 Year Ground Motion
FEMA P-58: Sample Outputs
New 8-story office in Los Angeles
Loss Ratio = 0.04
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New 8-story office in Los Angeles
37%32%
7%1% 1% 2% 1%
19%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
StructuralComponents
Partitions InteriorFinishes
Cladding Plumbing andHVAC
OtherComponents
Collapse Residual Drift
Loss Contributions by Component Type for a 475 Year Ground Motion
Loss Ratio = 0.15
FEMA P-58: Sample Outputs
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New 8-story office in Los Angeles
26%
12%
2% 2% 0% 1% 3%
54%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
StructuralComponents
Partitions InteriorFinishes
Cladding Plumbing andHVAC
OtherComponents
Collapse Residual Drift
Loss Contributions by Component Type for a 2475 Year Ground Motion
Loss Ratio = 0.44
FEMA P-58: Sample Outputs
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§ Average Repair Times (REDi, 2013):
0.8 0.9
3.5
0
2
4
6
8
10
12
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REDi Re-Occupancy REDi Functional Recovery REDi Full Recovery
MO
NTHS
Repair Time Output at a 43 Year Earthquake
FEMA P-58: Sample Outputs
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§ Average Repair Times (REDi, 2013):
6.0 6.3
9.2
0
2
4
6
8
10
12
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REDi Re-Occupancy REDi Functional Recovery REDi Full Recovery
MO
NTHS
Repair Time Output at a 475 Year Earthquake
FEMA P-58: Sample Outputs
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§ Average Repair Times (REDi, 2013):
10.7 11.0
13.1
0
2
4
6
8
10
12
14
REDi Re-Occupancy REDi Functional Recovery REDi Full Recovery
MO
NTHS
Repair Time Output at a 2475 Year Earthquake
FEMA P-58: Sample Outputs
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FEMA P-58 provides the comprehensive and standardizedbuilding-specific risk assessment.
SP3 software provides a user-friendly software to integrate all steps in a
FEMA P-58 risk assessment.
The initial assessment should take a couple hours and not days or
weeks.
FEMA P-58: Enabling SP3 Software
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§ Motivation – Current performance and the push for resilient design
§ The FEMA P-58 Methodology for assessing resilience:ü Overviewü Method enhancement for BRBFs
§ Updated resilience predictions for BRBFs§ Resilient design of BRBFs§ Summary and Q&A
Presentation Outline
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Site Hazard Structural Responses
Structural Components &
Fragilities
Nonstructural Components &
Fragilities
Building-Specific Vulnerability
Curves
Full distributions of losses and repair
times, and expected annual values.
FEMA P-58 Monte Carlo Analysis
ENGINE
FEMA P-58 Method Advancements for BRBFs
SP3 Structural Response Prediction ENGINE
“We do the nonlinear dynamic structural analysis for you.”
Component Fragility Database
(132 new fragilities specific to brace geometry and higher
ductility of CoreBrace BRBF data)
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Component Fragility Database
(132 new fragilities specific to brace geometry and higher
ductility of CoreBrace BRBF data)
FEMA P-58 Method Advancements for BRBFs
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• Comparison of new fragilities with standard FEMA P-58 fragilities (where the damage state is fracture of the brace requiring replacement)
FEMA P-58 baseline
CoreBrace
FEMA P-58 Method Advancements for BRBFs
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SP3 Structural Response Prediction ENGINE
“We do the nonlinear dynamic structural analysis for you.”
Specifically predict:– peak interstory drift– peak floor acceleration– residual interstory drift (a big focus)
FEMA P-58 Method Advancements for BRBFs
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FEMA P-58 Method Advancements for BRBFs
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Detailed nonlinear dynamic structural modeling, with many
building designs, was used to refine the residual drift model for CoreBrace BRBF buildings.
FEMA P-58 Method Advancements for BRBFs
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The FEMA P-58 default residual drift model is slightly conservative for
CoreBrace BRBFs (but only slightly).
FEMA P-58 Method Advancements for BRBFs
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Including a typical gravity system (beam/slab and
shear tab connections) in the nonlinear structural model
shows substantial reduction in residual drifts.
The FEMA P-58 default residual drift model is slightly conservative for
CoreBrace BRBFs (but only slightly).
FEMA P-58 Method Advancements for BRBFs
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Including a moment-connected back-up frame in
the nonlinear structural model shows even more
reduction in residual drifts. The typically designed back-up frames (sized for gravity) were sufficient and they did
not need additional requirements for the back-
up frames.
The FEMA P-58 default residual drift model is slightly conservative for
CoreBrace BRBFs (but only slightly).
Including a typical gravity system (beam/slab and
shear tab connections) in the nonlinear structural model
shows substantial reduction in residual drifts.
FEMA P-58 Method Advancements for BRBFs
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§ Motivation – Current performance and the push for resilient design
§ The FEMA P-58 Methodology for assessing resilience:ü Overviewü Method enhancement for BRBFs
§ Updated resilience predictions for BRBFs§ Resilient design of BRBFs§ Summary and Q&A
Presentation Outline
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§ We now want to see how the resiliency assessment results have changed based on these method improvements from the past 1.5 year of research and development (use a new mid-rise office building example in SDC D).
§ This comparison study was motivated by a more generalized study by the Applied Technology Council, in which the BRBF results appeared conservative.
FEMA P-58 Updated Risk Assessments
ATC Study Repair Costs for Various Structural Systems (Hooper et al. 2018)
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Study Overview:
FEMA P-58 Updated Risk Assessments
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Average Repair Costs (percentage building value):
FEMA P-58 Updated Risk Assessments
Step 1: Baseline ATC studyStep 2: Design for coupled strength/stiffnessStep 3: Consider gravity system, residual updatesStep 4: More ductile CoreBrace BRBF fragilitiesStep 5: Use moment-connected frame
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Average Repair Costs (percentage building value):
FEMA P-58 Updated Risk Assessments
Step 1: Baseline ATC studyStep 2: Design for coupled strength/stiffnessStep 3: Consider gravity system, residual updatesStep 4: More ductile CoreBrace BRBF fragilitiesStep 5: Use moment-connected frame
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Average Repair Times (FEMA P-58 “parallel” lower-bound time):
FEMA P-58 Updated Risk Assessments
Step 1: Baseline ATC studyStep 2: Design for coupled strength/stiffnessStep 3: Consider gravity system, residual updatesStep 4: More ductile CoreBrace BRBF fragilitiesStep 5: Use moment-connected frame
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Other Performance Metrics from FEMA P-58 – residual drifts and percentage repairable, many others available…
FEMA P-58 Updated Risk Assessments
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§ Motivation – Current performance and the push for resilient design
§ The FEMA P-58 Methodology for assessing resilience:ü Overviewü Method enhancement for BRBFs
§ Updated resilience predictions for BRBFs§ Resilient design of BRBFs§ Summary and Q&A
Presentation Outline
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§ To design a building to be resilient:ü Need no structural damage that requires repair (easy for a CoreBrace
BRBF)ü Need minimal residual drifts for no demolition (issue for ductile systems
like BRBFs but can be well controlled using a back-up moment frame)ü Need to either limit floor accelerations and/or design non-structural
components to resist them (BRBF yielding helps)ü Need to limit drifts to prevent other drift-sensitive non-structural
damage
§ Two resilient design options:a) Do direct resilient design using targets for downtime/losses and using
FEMA P-58 analysis method.b) Do indirect resilient design using modified building code requirements
(e.g. Risk Category IV), but such requirement have not yet been developed (in process).
c) For CoreBrace BRBFs: Use the Resilient Design Guide!
Resilient Design of CoreBrace BRBF Buildings
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Resilient Design of CoreBrace BRBF Buildings
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§ The FEMA P-58 methodology can provide quantitative resiliency predictions (repair costs and repair times).
§ Much research and development has been done to refine the FEMA P-58 methodology for BRBF buildings (fragilities and residual drifts).
§ The refined methods shows that damage and residual drifts are lower than previously predicted, though can still be an issue for such a ductile system. Even so, residual drifts can be controlled well by using a moment-resisting back-up frame.
§ Resilient design of CoreBrace BRBF buildings can now be done using either FEMA P-58 assessment or the Resilient Design Guide (available from CoreBrace.
Summary and Conclusions
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Closing and Questions
§ Thank you for your time.§ Our goal is to support adoption of resilience-based design and
risk assessment, and we welcome feedback and suggestions.
§ Time for questions!
Curt Haselton: [email protected], Direct: (530) 514-8980Tracy Rice (HB-Risk admin): [email protected]
www.hbrisk.comSP3 | where research meets practice