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Vulnerability Assessment of Buildings Contribution from

Large-scale Laboratory Tests

A. Pinto

ELSA, JRC, Ispra (VA), Italy

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Kocaeli (Turkey) Earthquake, August 17, 1999 (A. Elnashai, 1999)

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Mt. Parnes, Athens (Greece) Earthquake, Spet. 7, 1999 (M. Fardis & N. Bousias, 1999)

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Reinforced Concrete Buildings

Represent the largest part of the European building stock at risk, in earthquake prone urban areas

Many of the important structures [Hospitals, Schools, Emergency management, …] are RC structures

There is a lack of codified guidelines for seismic Assessment and Re-design, in Europe Design and Re-design may have different performance requirements

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Seismic Assessment &Retrofit of RC buildings

Design for earthquake resistance: No formal Seismic Design provisions- until the ‘50s in US and ‘60s in Europe

Issues/Difficulties Economical and political

High costs - compared with seismic resistance in new construction

Low premium market is willing to pay for higher safety

Tendency of politicians to avoid complex and socially sensitive problems

Provisions for design and detailing of members and structures: Standards in mid-’70s in US and mid-80s in Europe

Lack of control to the design, construction and maintenance processes

Why (causes)?

Technical Much easier to design a new ER

buildings than to assess and strength an old one

Lack of codified criteria and rules for redesign, which leads to somehow arbitrary interventions …(existing for masonry buildings …)

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Assessment --- Retrofitting

Assessment Determines the need for

seismic retrofit or not Identifies particular

weakness and deficiencies to be corrected

Requires: Tools to allow rapid

screening and empirical evaluation of existing structures

‘Solutions’: Conventional procedures Deformation and

displacement based evaluation procedures(Performance and model calibration from Lab Tests required)

Retrofitting To provide improved seismic

performance

Requirements: Technically feasible acceptable cost-benefit ratios

(cost benefit analysis)

Technical solutions according to the weakness

identified in the assessment procedure (local and/or global) and to the protection required:

• Stiffness

• Strength

• Ductility (deformation capacity)

• Damping or isolation

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Retrofitting ‘guidelines’ (General)

Key ideas Seismic retrofitting

combined with architectural remodeling, rehabilitation

and/or change in use Find a feasible and

acceptable solution allowing occupancy during the works

Technical Requirements Any intervention should not

prejudice the safety of any part of the building in any aspect

Continuity of the load path(s) between new and existing elements, floors, …

Foundations ?!

Retrofitting solutions New Shear-walls

Drift control, May solve irregularity problems, Design according to new codes, Foundations?!

Steel Bracing (with/out dissipation devices)

Very effective Connection between bracing

and concrete very peculiar

Jacketing (Steel, RC, FRC)

Element strength and deformation capacity (local)

Joints ?!

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ICONS - Topic 2Assessment Strengthening & Repair

ELSA

TMR-Large-scale Facility

European Laboratory for Structural Assessment (ELSA)

EC, Joint Research Centre, ISIS, SSMU, TP480

2120 Ispra (VA), Italy

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Assessment Strengthening & Repair

The research work is part of research programme of the

ICONS TMR-Network

Project Participants:E.C. Carvalho, E. Coelho, A. Campos-Costa, LNEC, Lisbon (PT)

A.S. Elnashai, R. Pinho, Imperial College of London (UK)M.N. Fardis, S.N. Bousias, G. Tsionis, University of Patras (GR)

GM. Calvi, A. Pavese, M. Recla, University of Pavia (IT)P.E. Pinto, G. Monti, University of Rome (IT)

J. Bouwkamp, S. Gomez, University of Darmstadt (DE)E. Alarcon, R. Perera, H. Lutz, Univ. Politecnica of Madrid (ES)

A. Plumier, University of Liege (BE)JM. Reynouard, INSA de Lyon (FR)

A.V. Pinto, G. Verzeletti, J. Molina, H. Varum, ELSA, JRC, Ispra (IT)

Other Contributions:

M. Griffith, University of Adelaide, Australia

The tests at the ELSA laboratory were financed under the TMR - Large-scale Facilities programme of the European Commission

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Tests on 4-storey RC Frames Objectives

Assessment of a typical RC frame representative of existing buildings

Design and Construction practice of 40~50 years ago • Simplified design (8% seismic coefficient), (concrete - C16/20, Steel -

Smooth rounded bars), lap-splicing, 90 degrees bent stirrups, no shear reinforcement in joints, Strong beam - Weak column system

Bare frame vs masonry Infilled frame

Assessment of retrofitting schemes and techniques Selective Retrofitting solutions

(balancing Ductility, Strength and Stiffness) Shotcrete of existing infill masonry walls K-bracing with shear-link (additional strength and damping)

Other aspects (Plastic-hinge length, Slab participation, Shear and bending deformations of Stocky column, Joints’ behaviour …)

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Frame lay-out

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Beam Reinforcement

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Column Reinforcement

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The ICONS Frame

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Transport

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ICO

NS

Fra

mes

Specimen A

Specimen B

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Test ProgramS

peci

men

BS

peci

men

A

Bare Frame (BF) Selective Retrofit (SR)

Infilled Frame (IN) Shotcrete (SC)

K-Bracing/Shear-link (KB)

Cyclic Test

PSD Tests

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Bare Frame and Selective Retrofit Frame Tests

Testing Programme Pseudo-dynamic tests for increasing earthquake

intensities (475, 975 and 2000 yrp)

A ‘complete’ measuring system Global (Storey forces and displacements) Local refined [rotations, deformations (joint, slab, column,

beam)] Photographic and video documentation

Detailed damage descriptions Damage categorization, Reparability …

Vulnerability and ultimate capacity Quantify Improved performance of retrofitted frame

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Instrumentation (Inclinometers)

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Instrumentation (Local)

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Earthquake Test at ELSA

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BARE FRAME3rd storey - Shear-Drift diagrams

475 yrp975 yrp

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BARE FRAME

0

1

2

3

4

0 0.5 1 1.5 2 2.5 3

Drift (%)

Sto

rey

475 yrp

975 yrp

Max. Inter-storey Drift Profiles

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BARE FRAME975 yrp test

3rd Storey collapse

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Selective Retrofitting Schemes

A

A ' S e c t i o n A - A '

S t e e l P l a t e s ( F e 4 3 0 )

60

12

0

60

19

0

B B '

12

0

19

0

Strength-only intervention

Ductility-only intervention

(Elnashai and Pinho, 1999)

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Selective Retrofitting Schemes

Strength-only intervention

Ductility-only intervention

Ductility andStrength intervention

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Max. Inter-storey Drift Profiles

REPAIRED FRAME

0

1

2

3

4

0 0.5 1 1.5 2 2.5 3 3.5

Drift (%)

Sto

rey

475 yrp

975 yrp

2000 yrp

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Max. Drift Profiles

BARE FRAME

0

1

2

3

4

0 0.5 1 1.5 2 2.5 3

Drift (%)

Sto

rey

475 yrp

975 yrp

REPAIRED FRAME

0

1

2

3

4

0 0.5 1 1.5 2 2.5 3 3.5

Drift (%)

Sto

rey

475 yrp

975 yrp

2000 yrp

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Global Drift

0

0.25

0.5

0.75

1

1.25

1.5

1.75

2

1 1.2 1.4 1.6 1.8 2

Input Intensity (Acc_max/Acc_ref)

Glo

ba

l Dri

ft (

%)

Bare Frame (BF)

Collapse of BF

Selective Retrofit (SR)

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Max. Inter-storey Drift

0

0.4

0.8

1.2

1.6

2

2.4

2.8

1 1.2 1.4 1.6 1.8 2

Input Intensity (Acc_max/Acc_ref)

Dri

ft (

%)

Bare Frame (BF)

Collapse of BF

Selective Retrofit (SR)

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Storey Maximum-Shear Profiles

0

1

2

3

4

0 50 100 150 200 250 300

Shear (kN)

Sto

rey

BF 475BF 975SR 475SR 975SR 2000

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Infilled Frame with openings

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Infill construction

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Max. Drift Profiles

BARE FRAME

0

1

2

3

4

0 0.5 1 1.5 2 2.5 3

Drift (%)

Sto

rey

475 yrp

975 yrp

INFILLED FRAME

0

1

2

3

4

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Drift (%)

Sto

rey

475 yrp

975 yrp

2000 yrp

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Shear-Drift (Storey 1)Infilled and Bare Frame

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Global Drift

0

0.25

0.5

0.75

1

1.25

1.5

1.75

2

1 1.2 1.4 1.6 1.8 2

Input Intensity (Acc_max/Acc_ref)

Glo

ba

l Dri

ft (

%)

Bare Frame (BF)

Collapse of BF

Selective Retrofit (SR)

Infilled Frame (IN)

Infilled Frame (IN)

Trend (IN)

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Max. Inter-storey Drift

0

0.4

0.8

1.2

1.6

2

2.4

2.8

1 1.2 1.4 1.6 1.8 2

Input Intensity (Acc_max/Acc_ref)

Dri

ft (

%)

Bare Frame (BF)

Collapse of BF

Selective Retrofit (SR)

Infilled Frame (IN)

Infilled Frame (IN)

Trend (IN)

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Shotcrete

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“Shotcrete”

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Max. Drift Profiles

INFILLED FRAME

0

1

2

3

4

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Drift (%)

Sto

rey

475 yrp

975 yrp

2000 yrp

SHOTCRETE

0

1

2

3

4

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Drift (%)

Sto

rey

475 yrp

975 yrp

2000 yrp

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Shear-Drift (Storey 1)Shotcrete and Infilled Frame

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Column Shear-out

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Column Shear-out

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Max. Inter-storey Drift

0

0.4

0.8

1.2

1.6

2

2.4

2.8

1 1.2 1.4 1.6 1.8 2

Input Intensity (Acc_max/Acc_ref)

Dri

ft (

%)

Bare Frame (BF)

Collapse of BF

Selective Retrofit (SR)

Infilled Frame (IN)

Infilled Frame (IN)

Trend (IN)

Shotcrete (SC)

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Response maximum values

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Concluding Remarks

RC frame Assessment

Storey mechanism ~1% drift for DE Collapse for 1,4xDE

(~2.5% drift)

RC frame with infills Assessment

Much Higher resistance Hiding irregularity Much Lower deformation

demands Structural integrity for 1.4xDE

but heavy damage to infills Story mechanism markedly

prompted after peak resistance (Softening)

Selective Retrofitting ‘Too good to be true’

well known structural characteristics, high costs, no infills

Withstanding 1.8xDE without serious damages and a stable dissipation mechanism (~3%Drift)

Infill Shotcrete Infill protection Slight lower softening and

higher ductility Column Shear-off (Shear-

out)

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ONGOING AND FUTURE PROJECTS AT ELSA

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SPEAR project (2001-2004)

Torsionally Unbalanced Structure to be tested at ELSA:

Simplification of an existing Greek 3-storey building

Designed for gravity loads Designed using the Greek

design code applied from 1954 to 1995

Doubly non symmetric plan configuration, regular in elevation

2-bay frames spanning from 3 to 6 m (10m x 10m)

3-DOF PsD Test

Partners:JRC (P. Negro), U.Patras (M. Fardis),

U.Pavia, U.Rome, IC-London, EQE-London, U.Ljubljana, U.Cyprus, LNEC-Lisbon,Other: ECOLEADER

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RC Flat-slab Structure (2002-3)

5.20

1.25

2.80

1.15

8.50

3.00 4.00 1.50

2.80 1.25

9.00

1.150.20

2.80

2.80

3.30

0.30

0.40

0.50

8.50

3.00 4.00 1.50

5.20

0.30

0.50

0.50

0.30

0.50

0.40

Shear-punching (detailing for seismic) Essentially non-dissipative (?) Significantly more flexible than

traditional frame/wall or frame structures Second order, P-d, effects

Additional measures for guiding conception and design

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JRC-ELSAInstitutional Programme (2003-6)

Creation of a Virtual Laboratory: - To link structural engineering

research sites across Europe, - Provide data storage facilities

and repositories,

- Offer remote access to the latest research tools, and - Enhance experimental techniques and procedures by full

exploitation of the electronic communication facilities (enlarged participation in testing preparation, conduction, analysis, distributed testing).

To explore the possibility of developing a common advanced platform for analytical/computational development and simulation