Building-Specific Risk Assessment and Resilient Design for … · 2018-03-17 · Building Code...

Edward AlmeterEngineering Researcher, Haselton Baker Risk Group

Curt B. Haselton, PhD, PEProfessor of Civil Engineering @ CSU, Chico

Co-Founder and CEO @ Haselton Baker Risk Group

www.hbrisk.com

SP3 Webinar Series

Building-Specific Risk Assessment and Resilient Design for Buckling-

Restrained Braced Frame Buildings

All phone lines are muted Questions are highly encourage (answered at end) Handouts are available – presentation slides Webinar is recorded and video will be distributed Please take a brief survey before signing off at end of webinar

Housekeeping

Questions:• Please use questions tab and we will

address as many as we can at the end of the webinar.

• For further questions, or for feedback on forward development, please contact Angie at HB-Risk and she can connect you with the right person (angie@hbrisk.com).

Housekeeping

Overview of SP3 Webinar Series:1) The new SP3 Structural Response Prediction Engine

[available at www.hbrisk.com]2) The new SP3 Building-Specific Risk Model

[available at www.hbrisk.com]3) SP3 Building-Specific Risk Assessment for tilt-up buildings

[available at www.hbrisk.com]4) SP3 Building-Specific Risk Assessment for Wood Light-Frame

Buildings [available at www.hbrisk.com]5) SP3 Building-Specific Risk Assessment and Resilient Design

of Buckling Restrained Braced Frame Buildings [today]

Housekeeping

Edward AlmeterEngineering Researcher, Haselton Baker Risk Group

Curt B. Haselton, PhD, PEProfessor of Civil Engineering @ CSU, Chico

Co-Founder and CEO @ Haselton Baker Risk Group

www.hbrisk.com

SP3 Webinar Series

Building-Specific Risk Assessment and Resilient Design for Buckling-

Restrained Braced Frame Buildings

Overview of FEMA P-58, current SP3 tools, and recent developments Specific goals for this BRBF project New SP3 models for BRBF buildings:

• Structural Response Prediction Engine for BRBFs (with focus on residual drifts)

• BRBF fragility functions (specific to geometry, etc.)• Sample results for building in Los Angeles

Resilient design of BRBF buildings Summary and next steps Question & Answer

Outline for Today

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: Fatalities &

injuries

FEMA P-58 Overview

Ground Motion Hazard

Component DamageEconomic Loss

Casualties

Repair Time

Structural Responses

SP3 uses FEMA P-58 and adds much more:

FEMA P-58 provides the comprehensive and standardized

building-specific risk assessment (with ~$16M to develop).

SP3 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.

SP3 Software Compliments FEMA P-58

Our Goal: To enable and facilitate rapid and advanced building-specific seismic riskassessments for all buildings (i.e. building-specific vulnerability curves).

Expected Outcomes: We believe that this will:

(a) facilitate the design of more resilient buildings, and(b) enable better risk-related decision making (e.g. insurance risk,

mortgage risk, etc.).

Our Goal with SP3

Recent “Rapid and Advanced” Research and Development:– No need for nonlinear structural analysis – “we do the structural

analysis for you” (Structural Response Prediction Engine) - Webinar #1– The new SP3 Building-Specific Risk Model now also automates many

other inputs (strength by age/location, period, etc.) - Webinar #2

Recent “For all Buildings” Research and Development:– Extended to tilt-up of all eras (beta) – Webinar #3– Extended to wood light-frame – Webinar #4– Now further refined for BRBF buildings – This Webinar– SP3 now supports rapid risk assessment for all common building types

other than URM.

Our Goal with SP3

Current SP3 Tools – Engineering

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

In the SP3_Engineering tool, inputs are done by a licensed

engineer on a building-specific and site-specific basis (with

some provided automation).

Curves

Basic Building and Site

Information(e.g. location, construction

year, etc.)

Additional Secondary Modifiers

(more building and site info.)

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

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)

Current SP3 Tools – SP3_RiskModel

Fragilities FEMA P-58 Monte Carlo

Analysis ENGINE

Fragilities

Curves

Basic Building and Site

Information(e.g. location, construction

year, etc.)

Additional Secondary Modifiers

(more building and site info.)

FEMA P-58 Monte Carlo

Analysis ENGINE

PGA and Sa for many hazard

levels

Site Hazards Database

Soil type

Structural responses(e.g. peak drift, floor acceleration,

residual drift; for ~100 motions)

Structural Response Prediction ENGINE

Structural Responses Database

Structural Models

Database

Dynamic Properties

ENGINE

Building Code Design Database

Site Soil DB

Struct. comp. inventory

Building strength

Experimental Test Database

Structural Designs

Database

Site-specific EQ and wind

strength design

Over-strength by bldg. type, location, etc.

Site-specific EQ and wind drift

design

Building stiffness (T1)

Building modal properties

(T2-T3, φ1-φ3)

Strength and stiffness of gravity and non-str.

components

Site-specific non-structural comp. design

Comp. Popul.

ENGINES

Non-str. comp. inventoryStruct. comp.

fragilitiesNon-str. comp.

fragilities

Component Fragility

Database

Current SP3 Tools – SP3_RiskModel

Goal: Expand P-58/SP3 risk analysis for BRBF buildings (without the user needing to create a NL structural model).

• Extend the SP3 Structural Response Prediction Engine to better predict responses of BRBF buildings, with specific focus on residual drifts.

• Expand the SP3 Fragility Database to have a new family of CoreBrace BRBF fragilities; make these specific to the high-ductility of CoreBrace BRBFs and make them geometry-specific (132 new fragilities).

• Include these new developments in both the SP3_Engineering tool (for full detailed engineering evaluations) and the SP3_RiskModel (which supports rapid evaluations for single-building to large inventories).

• Use these new developments to create Guidelines for Resilient Design of BRBF Buildings (in progress).

BRBF Project Goals

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)

SP3 Structural Responses Database

SP3 Structural Designs Database

SP3 Structural Models Database

BRBF Project Components

Outline for Today

Structural Modeling Goals

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)

Modeling Approach

• Designs from ATC-76 (NIST GCR 10-917-8) – 37 Archetypes available in report– 19 in seismic design category “Dmax” (SDS = 1.0, S1 = 0.6)

• 4 bracing configurations• 3 primary variants

– No gravity system– Gravity system– With backup frame (not designed as dual system)

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

0 2.5 5 7.5 10 12.5 15

Median Peak IDR / Yield IDR

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%

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.

0 2.5 5 7.5 10 12.5 15

FEMA P-58-1 eqn. 5-24

No Backup Frame

With Backup Frame

0 0.5 1 1.5 2 2.5 3

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

CoreBrace BRBFs (but only slightly).

0 2.5 5 7.5 10 12.5 15

FEMA P-58-1 eqn. 5-24

No Backup Frame

With Backup Frame

0 0.5 1 1.5 2 2.5 3

Including a typical gravity system (beam/slab and

shear tab connections) in the nonlinear structural model

shows substantial reduction in 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.

0 2.5 5 7.5 10 12.5 15

FEMA P-58-1 eqn. 5-24

No Backup Frame

With Backup Frame

0 0.5 1 1.5 2 2.5 3

Including a typical gravity system (beam/slab and

shear tab connections) in the nonlinear structural model

shows substantial reduction in residual drifts.

Modeling Results – Peak Interstory Drifts

• Peak interstory drift1) Predict roof drift from ASCE 41 target displacement2) Modify roof drift for inelastic responses (based on OpenSees model results)3) Allocate drift to stories based on elastic modal analysis (three modes)4) Localize story drifts based on level of inelasticity (function of S, strength ratio)

𝑆𝑆 =𝑆𝑆𝑎𝑎�𝑉𝑉𝑦𝑦 𝑊𝑊

Note that the presence of gravity system, as well as the backup frame, affect the response and this is accounted for in this method.

• Basic schematic of interstory drift prediction:

Method Results – Peak Floor Accelerations

• Peak floor acceleration– Predict based on elastic modal analysis (3 modes) and then saturate accelerations for

inelastic effects.– Saturation is a function of strength ratio, 𝑆𝑆.

• Basic schematic of PFA prediction:

Outline for Today

CoreBrace Fragilities

• 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

(in2 )

Single Diagonal

Chevron/VBrace ConfigurationStory Ht, H (ft)

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

Single Diagonal Chevron/V

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

(in2 )

Single Diagonal

Bolted

Pinned

Welded

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

(in2 )

Single Diagonal

• Core Brace Fragilities– Demand Parameter: Interstory drift ratio (IDR)

Bay Width (B)

)Bay Width (B)

Lateral Disp. (Δ)

𝐼𝐼𝐼𝐼𝐼𝐼 = �∆ 𝐻𝐻

• 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

Outline for Today

Sample Results – Mean Residual

Expected residual drifts:

Demolished

Sample Results - Demolition

Probability of demolition (using the standard FEMA P-58 residual drift capacity threshold of 1% permanent drift):

Sample Results - Demolition

Probability of demolition (using the standard FEMA P-58 residual drift capacity threshold of 1% permanent drift):

Sample Results – Mean Loss

Effects on mean losses:

Sample Results – Mean Loss

Effects on mean losses:

Outline for Today

“Resilient design” can mean a lot of things. Here we mean – limit damage, limit losses and building closure time;

essentially, don’t design a “safe but disposable” building.

Resilient Design of BRBF Buildings

A group outlined these concepts for a 2017

SEAOC paper.

“Resilient design” can mean a lot of things. Here we mean – limit damage, limit losses and building closure time;

essentially, don’t design a “safe but disposable” building.

A group outlined these concepts for a 2017

SEAOC paper.

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 that provides a restoring force.

3) Often 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).

Baseline from previous:

Step #1: Design BRBFs to not require structural repair (easy with

a standard CoreBrace BRBF design).

Step #2: Use a moment-connected back-up frame to provide an

elastic restoring force and control residual drifts (purple).

Step #3: Reduce design drift to protect non-structural

drift-sensitive components (e.g. drywall, cladding, etc.).

Resilient Design of BRBF BuildingsStep #3b: Redesign some non-

structural components to further reduce non-structural

drift-sensitive damage (e.g. cladding, etc.).

Resilient Design of BRBF BuildingsStep #4: Use real floor

acceleration demands (not ASCE7 demands) and redesign anchorages,

equipment, elevators, etc.).

Resilient Design of BRBF BuildingsStep #4: Use real floor

acceleration demands (not ASCE7 demands) and redesign anchorages,

equipment, elevators, etc.).

0 0.2 0.4 0.6 0.8 1

PFA (g)

0123456789

101112

12 Story BRBF(475 year motion)

I=1.00, S=3.04

I=1.25, S=2.54

I=1.50, S=2.18

I=1.75, S=1.91

I=2.00, S=1.70

Now that we have a refined P-58/SP3 risk assessment method for BRBF buildings, we can use this to create quantitative resilient design guidelines.

1 1.25 1.5 1.75 2

Drift Limit (%)

Los Angeles, 8 Story,475 year motion

Next steps for resilient design guidelines:• We will complete further parameter studies to quantify how

change to design requirements affect building resilience.• This will result in charts and tables similar to the design drift

figure on the last slide (e.g. what design drift do you need to use to get a 5% loss).

• We will then boil this down into design guidelines.• Note that, because the P-58/SP3 method is so building/site-

specific, these charts/guidelines differ between various buildings and sites (e.g. easily a 2x difference for site or for short vs. tall).

• With the P-58/SP3 method being so building/site-specific, the charts/guidelines will get you in the “design ballpark”, and then a P-58/SP3 analysis should be run to confirm the resilience of the final design.

Outcome: Expanded P-58/SP3 risk analysis for BRBF buildings (without the need for expensive nonlinear structural modeling):

• Extended the SP3 Structural Response Prediction Engine to better predict responses of BRBF buildings, with specific focus on residual drifts.

• Expanded the SP3 Fragility Database to have a new family of CoreBrace BRBF fragilities; make these specific to the high-ductility of CoreBrace BRBFs and make them geometry-specific (132 new fragilities).

• Included these new developments in both the SP3_Engineering tool (for full detailed engineering evaluations) and the SP3_RiskModel(which supports rapid evaluations for single-building to large inventories).

• Used these new developments begin creating Guidelines for Resilient Design of BRBF Buildings (ongoing).

Summary of Project Outcomes

Summary of SP3 Webinar Series:1) The new SP3 Structural Response Prediction Engine

[available at www.hbrisk.com]2) The new SP3 Building-Specific Risk Model

[available at www.hbrisk.com]3) SP3 Building-Specific Risk Assessment for tilt-up buildings

[available at www.hbrisk.com]4) SP3 Building-Specific Risk Assessment for Wood Light-Frame

Buildings [available at www.hbrisk.com]5) SP3 Building-Specific Risk Assessment and Resilient Design

of Buckling Restrained Braced Frame Buildings [today]

Summary of Webinars in this Series

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!

Ed Almeter: edward@hbrisk.comCurt Haselton: curt@hbrisk.com

Angie Carpenter (HB-Risk admin): angie@hbrisk.com

www.hbrisk.com

Questions:• Please use questions tab and we will

address as many as we can for the rest of our time.

• For further questions, or for feedback on forward development, please contact Angie at HB-Risk and she can connect you with the right person (angie@hbrisk.com).

Closing and Questions

Building-Specific Risk Assessment and Resilient Design for … · 2018-03-17 · Building Code...

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