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Building Collapse Fragilities Considering Mainshock-Aftershock Sequences Using

Publicly Available NEEShub Data

Yue Li and Ruiqaing SongMichigan Technological University

John W. van de Lindt The University of Alabama

Nicolas LucoUnited States Geological Survey

Integration of Mainshock-Aftershock Sequences Into Performance-Based Engineering Using Publicly Available NEEShub Data

John van de Lindt (Co-PI)University of Alabama

Nicolas Luco (Co-PI)United States Geological Survey

Yue Li (PI)Michigan Technological University

Graduate Students: Ruiqiang SongNegar Nazari NSF CMMI -1000567

Introduction

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• During earthquake events, it’s very common to observe many aftershocks following the mainshock (588 aftershock with magnitude 5 and greater recorded after the Earthquake in Japan 2011).

Tohoku Aftershock

• Although smaller in magnitude, aftershocks may have a large ground motion intensity, longer duration and different frequency content

Motivation

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• Potential to cause severe damage to buildings and threaten life safety even when only minor damage is present from the mainshock

• However, most of current seismic risk assessment focus on risk due to a mainshock event only

February 2011 Christchurch Earthquake

Research Challenges

• Significant uncertainty in collapse capacity of damaged buildings after the mainshock

• Characteristics of aftershocks are quite complex

• Lack of system fragility models to evaluate building performance

PBE objectives

Task 1Design portfolio

Task 2Global-level hysteresis

damage model

Design/retrofit options

Consider aftershock?

PBE frameworkmainshock only

Mainshock-aftershock sequence simulation

Task 3Fragility generation for

degrading systems

Task 4Integration of

aftershock hazard with PBE

Satisfied performance expectation?

Task 5Illustration and Integration

into Existing Methodologies

Numerical modelselection

Building No.

Building Type Brief Description

1 Steel Three-story steel building with ordinary moment frame

2 Steel Four-story steel building with special moment frame

3 Steel Eight-story steel building with special moment frame

4 Light-frame Wood

Two-story light commercial building

5 Light-frame Wood

Three-story apartment building

Pcollapse =

[ | ] | ( ) |aCollapseP S x dH x

Seismic Rehabilitation of Existing Buildings

Tested Steel Structure at NEES @ Buffalo

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• A typical 4-story 2-bay steel moment frame

(1/8 scale) is selected

(Lignos and Krawinkler 2011)

Calibration of Prototype and Test model

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ResultsNatural period in the EW direction Pushover analysis in EW direction

T1 T2 T3 Peak based shear/weight Maximum roof drift

Lignos Thesis 1.32 0.39 0.19 0.2 8.2%

Centerline model 1.32 0.44 0.24 0.2 8.2%

• The first three modal periods, pushover curve, fragility curves and time history response of prototype and test model are calibrated

2010 - 2011 Canterbury Earthquake Records at Resthaven, New Zealand

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Structural Collapse Capacity

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• 22 Far-Field records and 28 Near-Field records from

FEMA P695

• Preform incremental dynamic analysis (IDA) to determine structural collapse capacity

Damaged Building from Mainshock

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• In order to obtain the specific structural damage condition sustained from mainshock, the intensity level of mainshock is scaled to cause the following drift defined in ASCE/SEI 41-06

Damage Level Drift

Immediate occupancy 0.7% transient

life safety 2.5% transient

collapse prevention 5% transient

Structural Collapse Capacity

Difference Damage Level from Mainshock + Aftershock

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Structural Collapse Capacity

Difference Damage Level from Mainshock + Aftershock

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Structural Collapse Capacity

Mainshock Damaged Building + Different Aftershocks

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Structural Collapse Capacity

Mainshock Damaged Building + Different Aftershocks

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Collapse Fragility Curves

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Combination of Mainshock-aftershock Sequences

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1. Mainshock + repeated aftershock (Far-Field)

2. Mainshock + random aftershock (Far-Field)

3. Mainshock (Far-Field) + aftershock (Near-Field)

4. As-recorded mainshock + aftershock sequences

Collapse Capacity for MS-AS Sequences

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Summary and On-going Research

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• Damaged building from mainshock may have significantly reduced collapse capacity

• Structural collapse capacity depends on combination of mainshock - aftershock sequences, particularly the frequency contents in earthquake ground motions

• Investigation of portfolio of representative steel buildings

• Effects of as-record MS-AS sequences to be investigated

• Wood frame buildings – collaborative work at University of Alabama (Prof. John van de Lindt, Co-PI)

Thank you!

Contact Information:

Dr. Yue Li

Associate Professor Michigan Technological University

yueli@mtu.edu