POST-EARTHQUAKE RESIDUAL CAPACITY OF REINFORCED CONCRETE : Draft Framework

K. Elwood QuakeCoRE Director MBIE Chair in Earthquake University of Auckland

Representing: MBIE (NZ) Working Group on Residual Capacity A. Cattanach, A. Cuevas Ramirez, M. Kral, K. Marder, S. Pampanin, P. Smith, M. Stannard Christchurch Damage Statistics

Damage Ratio≈ repair cost ⁄ replacement cost 223 RC Buildings over 2 stories (visual estimate) (Kim et al. 2015) Demolish Repair Unknown 80(36%) Total

55(25%) 54(24%)

43 43 32 20(9%) 24 13(6%) 20 19 1(0%) 3 13 8 3 0 1 121 0 1 0 0

0-1% 2-10% 11-30% 31-60% 61-99% 100%  Significant number of RC buildings with relatively low damage were demolished. External factors:

100%

80%

60%

40%

20%

0% Economic losses covered by by insurance covered losses Economic Canterbury, Chile Tohoku, L'Aquila, Turkey NZ (2011) (2010) Japan Italy (2009) (2011) (2011)

SwissRe, 2013 Demolition Decision Framework - Marquis et al. 2015 When is residual capacity important?

In post-earthquake situations, RC buildings can be broadly categorized into three categories:

1. Minimal damage: no 2. Heavy damage: 3. Moderate damage: further action demolition is residual capacity? required necessary When is residual capacity important?

Non-structural damage – Economically important – Does not affect structural capacity

Non-ductile damage – Likely requires full retrofit or replacement

Moderately damaged Flexural damage (plastic hinging) - Outcome less clear building - Need guidance on residual capacity Draft Framework

GROUND MOTION & STRUCTURAL DRAWINGS OBSERVABLE DAMAGE CREATE BUILDING MODEL CRACK DISTRIBUTIONS AND PERFORM ANALYTICAL CRACK WIDTHS ESTIMATION OF PEAK RESIDUAL DRIFT BUILDING RESPONSE ETC...

How to reconcile? LOW-CYCLE BEST ESTIMATE OF PEAK DEMANDS FATIGUE ASSESSMENT Impact of loading rate, protocol, strain ageing? PROCEDURE CALCULATE RESIDUAL STIFFNESS, STRENGTH, & DEFORMABILITY FOR DAMAGED/REPAIRED COMPONENTS Epoxy? IS REPAIR UPDATE BUILDING MODEL TO ACCOUNT FOR REQUIRED? DAMAGED/REPAIRED COMPONENTS

RE-CONDUCT ANALYSIS USING UPDATED MODEL BUILDING CAPACITY RELATIVE TO UNDAMAGED BUILDING Criteria for demolish/repair recommendation? Draft Framework: Research needs

1. Define plastic hinges based on observed damage. 2. When is detailed assessment of bar strain necessary? 3. Observed damage  peak demands 4. When to consider low-cycle fatigue (LCF)?  LCF residual capacity? 5. Peak demand  Stiffness and strength degradation – Influence of strain rate, crack distribution, strain ageing, etc 6. Epoxy repair  Stiffness and strength degradation 7. Criteria for repair or demolition recommendation. Ongoing Research: UA study - Experimental study

Baseline Static Tests to Failure

Cyclic Monotonic

Member Section 4/5 scale from Red Book building Ongoing Research: UA study - Loading Protocol

Complete standard cyclic Run 1: Cycles at or below peak drift loading protocol Displacement from Run 1 left out of Run 2 as applied in demands from baseline test EQ (Dynamic)

Low or moderate drift level

Run 2: Cycles above peak drift from Run 1 Epoxy No Repair Specimen Specimen Research:Ongoing study UA - from analysis of of analysis from loading EQ Dynamic 1: Run Unrepaired vs. repaired vs. Unrepaired No repair Bldg Epoxy to failure to loading cyclic Static 2: Run left to “age” after Run 1: Run after “age” to left be will specimens Two Strain aging Loporcaro,et al, 2014 Ongoing Research: UA study - Cyclic vs Monotonic ) kN

Limited influence of cycles at Shear ( moderate-high drift demand (<2.5%).

2.5% Lateral Drift (%) Elephant in the room…

• Post-earthquake demolition decisions. • Engineers need to lead this decision process, not follow. • Need guidance on assessment of Residual Capacity. – International Challenge Supported by:

Thank you!

Impact of Uncertainty in

Structural AssessmentsUncertainty in Post-EQ Assessments with guidance Uncertainty in Post-EQ Assessments w/o guidance Engineer hired by building by owner hired Engineer Engineer hired by insurance company insurance by hired Engineer

0 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Damage≈ Ratio repair cost ⁄ replacement co Repaired after Specimen name1 Initial damaging loading type Failure loading type initial damage? Cyc - Static cyclic No Mono - Static monotonic No Cyc-ER - Static cyclic No Mono-ER - Static monotonic No Static cyclic (cycles above LD-1.5 Dynamic long duration ~1.5% drift No 1.5% drift only) Static cyclic (cycles above LD-1.5-R Dynamic long duration ~1.5% drift Yes 1.5% drift only) Static cyclic (cycles above LD-2.5 Dynamic long duration ~2.5% drift No 2.5% drift only) Static cyclic (cycles above LD-2.5-R Dynamic long duration ~2.5% drift Yes 2.5% drift only) Static cyclic (cycles above P-1.5 Dynamic pulse-type ~1.5% drift No 1.5% drift only) Static cyclic (cycles above P-1.5-R Dynamic pulse-type ~1.5% drift Yes 1.5% drift only) Static cyclic (cycles above P-2.5 Dynamic pulse-type ~2.5% drift No 2.5% drift only) Static cyclic (cycles above P-2.5-R Dynamic pulse-type ~2.5% drift Yes 2.5% drift only) Static cyclic (cycles above LD-2.5-SA* Dynamic long duration ~2.5% drift No 2.5% drift only) Static cyclic (cycles above LD-2.5-SAR* Dynamic long duration ~2.5% drift Yes 2.5% drift only) 1. Review Proposed Building Procedure: Drawings 3. Inspect Building 2. Develop building - system level model and perform - component level AISPBE analysis - Material level

4. Compare peak demands from model and observed 5. Estimate demands from damage distribution in damaging earthquake building. Update model.

7. Determine damaged 6. Assess if (or repaired) component no performance yes Use LCF characteristics controlled by Low assessment Cycle Fatigue procedure (LCF) 8. Update building model and conduct AISPBE repaired analysis unrepaired

8a. Unrepaired damaged 8b. Repaired building building subjected to design subjected to design (ULS) (ULS) earthquake demand earthquake demand Repair design OK else %NBS >B else %NBS >B