seismic risk assessment & resilient design of brbf buildings … · 2019-06-13 · seismic risk...

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Seismic Risk Assessment & Resilient Design of BRBF Buildings

using the FEMA P-58 Analysis Method

Presented by: D. Jared DeBock, PhD, PEAssistant Professor of Civil Engineering @ CSU, Chico

Senior Research Engineer @ Haselton Baker Risk Group (SP3)

Presented on Behalf of: The Full SP3 TeamCurt B. Haselton, Jack Baker, Katie Wade, Ed Almeter,

Shaunt Kojabashian, Mike McGlone, Tracy Rice, and Dustin Cook

SP3 | where research meets practicewww.hbrisk.com

NASCC Technical Presentation | April 3, 2019

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Motivation – What we get from code-based design, and current pushes for “functional recovery” design FEMA P-58 analysis methods for assessing resilience

(losses and downtime) Research to enable accurate FEMA P-58 analysis for

BRBF buildings Approaches to resilient design of BRBF buildings Summary and Q&A

Agenda for Today

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Agenda for Today

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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 Seismic Design Methods

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What is Code-Based Design Providing?

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15%

50%

Performance expectations for a sample building 8-story office building Northridge, CA Performance estimated from FEMA P-58 and the SP3-

RiskModel

8 mo.

> 1 yr.

Example Code-Conforming Building

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Repair Costs for Various CA Cities

New 8-story office building at 12 CA cities

~5-20%~10-80%

Design Event Rare Event

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New 8-story office building at 12 CA cities

7-10 mo.

7-18 mo.

Design Event Rare Event

Downtime for Various CA Cities

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Performance of CA Buildings by Location

Loss for the 10% in 50 year Hazard

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Summary for a wide range of building types: 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!).

Summary of Expected Performance

Hence, we refer to these buildings as safe but

disposable for a rare event!

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Summary of Expected Performance

Why are we seeing expected damage/closure and performance that is inconsistent by location?

Code design objectives: Safety: “Safe” at the MCE Losses: Not considered for Cat. II, some for Cat. IV. Downtime: Not considered for Cat. II, some for Cat. IV.

Resulting basic design philosophy: Allow structural damage by using 1.0/R with ductile members. Allow non-structural damage (by using 1.0/R or not designing to

prevent damage).

Should we be considered loss/downtime in design?

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California Assembly Bill 393 – “functional recovery” code provisions for California NEHRP Reauthorization – Congress tasked NIST with

recommendations for design for functional recovery Cities like San Francisco – considering enhanced design

requirements for tall buildings (to consider functionality)

A Push for Resilient Design (Functional Recovery)

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Agenda for Today

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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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FEMA P-58: Overview

Ground Motion Hazard

Component DamageEconomic Loss

Casualties

Repair Time

Structural Response

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FEMA P-58: Benefits

Comprehensive and credible: $16M, 15 years to develop, team of 100+ really smart researchers and practitioners. Standardized and repeatable: Consistent FEMA P-58 damage and

repair cost databases are used consistently for all analyses (created based on 20+ years of research). Building-specific: The analysis incorporates the specific nuances

of the building, rather than being based on a building class. Transparent and open-source: FEMA P-58 is open to the public

and you can see all the details of how the assessment is done.

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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 and Enabling Software

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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**)

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FEMA P-58: Component Damage

Step 3: Quantify component damageFirst, establish what components are in the building. Types and quantities 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


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**)


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 $26,892

Partitions $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.


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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 and Components• Fragility curves

Step 4: Loss Estimation (loss curves & other 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

Output Examples: Repair Cost

8-story concrete frame in Los Angeles

Loss Ratio = 0.04

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37%32%

7%1% 1% 2% 1%

19%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%




OtherComponents



Loss Ratio = 0.15

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26%

12%

2% 2% 0% 1% 3%

54%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%




OtherComponents



Loss Ratio = 0.44

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Output Examples: Repair Times

Average Repair Times (REDi, 2013):

0.8 0.9

3.5

0

2

4

6

8

10

12

14

REDi Re-Occupancy REDi Functional Recovery REDi Full Recovery

MO

NTH

S

Repair Time Output at a 43 Year Earthquake

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6.0 6.3

9.2

0

2

4

6

8

10

12

14


MO

NTH

S


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10.7 11.0

13.1

0

2

4

6

8

10

12

14


MO

NTH

S


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Output Examples: Fatalities and Injuries

Safety (fatalities and injuries):

0.20.0 0.0 0.0

0.20.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Injuries (FromFalling Hazards)

Fatalities (FromFalling Hazards)

Injuries (FromCollapse)

Fatalities (FromCollapse)

Total Injuries Total Fatalities

Mean Casualties at a 43 Year Earthquake

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1.3

0.0 0.0 0.0

1.3

0.00.0

0.5

1.0

1.5

2.0

2.5

3.0







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2.5

0.00.1

0.8

2.6

0.8

0.0

0.5

1.0

1.5

2.0

2.5

3.0







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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 (initially released in 2014).

The initial assessment should take a couple hours and not days or weeks.

Enabling SP3 Commercial Software

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Enabling SP3 Commercial Software

The Goal: Enable widespread and mainstream use of FEMA P-58 for building-specific seismic risk assessment.

The Intended Outcome: We believe that this better understanding of risk will:

(a) facilitate design of more resilient buildings and

(b) enable better decision-making for both mortgage risk and insurance risk.

The Strategy: Provide a software that enables these assessments at a rapid pace, so it’s feasible to use for nearly all projects (taking hours, not days or weeks).

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SP3-Design



Fragilities


Fragilities FEMA P-58 Monte Carlo Analysis

ENGINE


Repa

ir Co

sts

Ground Shaking

Repa

ir Ti

me

Ground Shaking

Detailed Building and Site

Information

(e.g. structural system and layout,

non-structural components, etc.)

SP3-Design

Licensed Engineer: In the SP3_Engineering tool, inputs are done by a licensed engineer on a

building-specific and site-specific basis (with some

provided automation).

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We released SP3-Design in 2014, with the primary focus on structural engineering designers (new design and retrofit). We have been excited to see SP3-Design used on a wide range of

exciting projects by 85+% of large west coast structural engineering firms, such as:

– Resilient design of new buildings (municipal buildings, court houses, etc.)

– Retrofit of existing buildings– Assessments of special facilities (EOCs, manufacturing, museums, etc.)– Mortgage risk assessments – Investment risk assessments – Insurance risk assessments

FEMA P-58 and SP3 Use-Cases

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Fragilities



ENGINE

SP3-RiskModel

Basic Building and Site

Information(structural system, number of stories,

location, construction year)

Additional Secondary Modifiers(drift limit,

importance factor, strength,

period, configuration irregularities,

etc.)

SP3 Building-Specific Risk Model




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Fragilities



ENGINE

SP3-RiskModel

Basic Building and Site

Information

Additional Secondary Modifiers(drift limit,

importance factor, strength,

period, configuration irregularities,

etc.)

SP3 BUILDING-SPECIFIC RISK MODEL

Full FEMA P-58 engineering-based risk assessment framework

Automation through many research-backed analytical SP3 Engines and SP3 Databases

(Building Code Database, Archetype Design Database, Structural Response Engine, etc.)

When full automation is used, this provides building-specific and site-specific vulnerability

curves quickly and can be used for large inventories (with support from SP3-Batch)




(structural system, number of stories,

location, construction year)

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Agenda for Today

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Fragilities


Fragilities




FEMA P-58 Monte Carlo Analysis

ENGINE

Research Needed for FEMA P-58 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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Structural Responses

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)

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Overview of Structural Modeling

• Designs from ATC-76 (NIST GCR 10-917-8) – 37 building design archetypes, with 19 in SDC Dmax

– 4 bracing configurations– Used NIST Guidelines for Nonlinear Structural Analysis for

Design of Buildings for the nonlinear modeling (ATC 114)• Three primary model variants

– No gravity system (just the braces)– With gravity system– With backup frame (not designed as dual system)

• OpenSees used for modeling (with 44 ATC-63 ground motions)

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Overview of Structural Modeling

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0 2.5 5 7.5 10 12.5 15

Median Peak IDR / Yield IDR

0

2

4

6

8

10

12

Med

ian

Res

idua

l ID

R /

Yiel

d ID

R

FEMA P-58-1 eqn. 5-24

No Backup Frame

No Backup Frame With Gravity

With Backup Frame

0 0.5 1 1.5 2 2.5 3

Median IDR (%) for y = 0.2%

0

0.4

0.8

1.2

1.6

2

2.4

Med

ian

Res

idua

l ID

R (%

) for

y =

0.2

%

Modeling Results – Residual Drifts

Detailed nonlinear dynamic structural modeling, with many building designs, was

used to refine the residual drift model for CoreBrace BRBF buildings.

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0 2.5 5 7.5 10 12.5 15


0

2

4

6

8

10

12

Med

ian

Res

idua

l ID

R /

Yiel

d ID

R

FEMA P-58-1 eqn. 5-24

No Backup Frame


With Backup Frame

0 0.5 1 1.5 2 2.5 3


0

0.4

0.8

1.2

1.6

2

2.4

Med

ian

Res

idua

l ID

R (%

) for

y =

0.2

%

The FEMA P-58 default residual drift model is slightly conservative for CoreBrace

BRBFs (but only slightly).

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0 2.5 5 7.5 10 12.5 15


0

2

4

6

8

10

12

Med

ian

Res

idua

l ID

R /

Yiel

d ID

R

FEMA P-58-1 eqn. 5-24

No Backup Frame


With Backup Frame

0 0.5 1 1.5 2 2.5 3


0

0.4

0.8

1.2

1.6

2

2.4

Med

ian

Res

idua

l ID

R (%

) for

y =

0.2

%


Including a typical gravity system (beam/slab and shear tab connections) substantially reduces

residual drifts.



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0 2.5 5 7.5 10 12.5 15


0

2

4

6

8

10

12

Med

ian

Res

idua

l ID

R /

Yiel

d ID

R

FEMA P-58-1 eqn. 5-24

No Backup Frame


With Backup Frame

0 0.5 1 1.5 2 2.5 3


0

0.4

0.8

1.2

1.6

2

2.4

Med

ian

Res

idua

l ID

R (%

) for

y =

0.2

%




Including a typical gravity system (beam/slab and shear tab connections) substantially reduces

residual drifts.

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.

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Component Fragility Functions

Component Fragility Database

(132 new fragilities specific to brace geometry and higher

ductility of CoreBrace BRBF data)

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CoreBrace Fragilities

• 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

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• Coverage: Standard CoreBrace braces– Brace configuration– Connection detail– Steel core area

14 16 20 14 16 20 14 16 20 14 16 2030 30 30 20 20 20 20 20 20 15 15 15

2.14 1.88 1.50 1.43 1.25 1.00 1.43 1.25 1.00 1.07 0.94 0.75

5Bolted Pinned Welded

Bolted Pinned Welded



































30Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Asc

(in2 )

Single Diagonal

Chevron/VBrace ConfigurationStory Ht, H (ft)

Bay Width, B (ft)Bay/Story Height Ratio

Single Diagonal Chevron/V

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14 16 20 14 16 20 14 16 20 14 16 2030 30 30 20 20 20 20 20 20 15 15 15

2.14 1.88 1.50 1.43 1.25 1.00 1.43 1.25 1.00 1.07 0.94 0.75





































30Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Asc

(in2 )

Single Diagonal



Bolted

Pinned

Welded

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14 16 20 14 16 20 14 16 20 14 16 2030 30 30 20 20 20 20 20 20 15 15 15

2.14 1.88 1.50 1.43 1.25 1.00 1.43 1.25 1.00 1.07 0.94 0.75





































30Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Bolted Pinned

Asc

(in2 )

Single Diagonal



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Sample Mean Losses for an 8 Story BRBF in Long Beach, CA

More detail on BRBF seismic resilience will be presentedon Friday by our CEO Curt Haselton(Friday 10:45-11:45am in Room 261)

Sample Risk Assessment Results

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0 2.5 5 7.5 10 12.5 15


0

2

4

6

8

10

12

Med

ian

Res

idua

l ID

R /

Yiel

d ID

R

FEMA P-58-1 eqn. 5-24

No Backup Frame


With Backup Frame

0 0.5 1 1.5 2 2.5 3


0

0.4

0.8

1.2

1.6

2

2.4

Med

ian

Res

idua

l ID

R (%

) for

y =

0.2

%

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Questions: Can we do better in the design process (and should we)? If we want more resilient design to meet loss and downtime

goals in addition to safety goals, what should we do?

Two overall options:1) Use knobs we already have in the building code (strength,

drift, risk category, etc.)2) Use a direct resilient design approach using FEMA P-58

Resilient Design

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1) Keep brace strains low enough to not have fracture and

not need repair (easy with CoreBrace BRBFs).

2) Control residual drifts through use of a back-up frame or additional strength/stiffness.

3) Possibly reduce design drift to prevent drift-sensitive non-structural damage (same for

any structural system).

4) Prevent acceleration-sensitive non-structural

damage by either strengthening anchorages and/or controlling

floor acceleration demands (easier for BRBFs because PFAs are lower than elastic building).

1)

2)

3)

4)

Resilient Design of BRBF Buildings

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Resilient Design of BRBF Buildings

Report:“Resilient Design Guidelines for CoreBraceBuckling Restrained Brace Frame Buildings”

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Code-based design gives us safe, but disposable buildings FEMA P-58 can be used for site-specific, building-specific

seismic risk assessment A structural response prediction method for CoreBrace

BRBFs is available in SP3 Gravity system and Back-up frames significantly reduce

residual drifts

Structural component fragilities specific to CoreBraceBRBFs are implemented in SP3 Practical guidelines for resilient design of BRBFs are

publically available

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!

Tracy Rice (HB-Risk admin): [email protected] Haselton: [email protected], Direct: (530) 514-8980

www.hbrisk.com

seismic risk assessment & resilient design of brbf buildings … · 2019-06-13 · seismic risk...

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