Urban Habitat Constructions under Catastrophic EventsFINAL CONFERENCE. Naples, 16th- 18th September 2010Chair of the Action: Federico Mazzolani, IT, fmm@unina.itCOST Science Officer: Thierry Goger, tgoger@cost.esf.org

COST Action C26

ASSESSMENT OF THE ROBUSTNESS OF STRUCTURES SUBJECTED TO FIRE FOLLOWING EARTHQUAKE THROUGH A PERFORMANCE-BASED APPROACH

B. Faggiano, D. De Gregorio & F. M. Mazzolani

University of Naples ‘Federico II’, Naples, ITALY

INTRODUCTION

The analysis of the behaviour of structures under the effect of fires following an earthquake is a significant research field, which is not yet fully explored. The high probability of occurrence of firesin civil and industrial buildings after being struck by a seismic shake justifies the need to investigate the response to high temperatures of the structural systems, they being already in a state ofirreversible deformed configuration due to earthquake. In order to preliminary take into account in the design phases the effect of the combination of the seism and fire accidental loads, thepaper presents a proposal for a methodology aimed at the robustness assessment under fire of structures already damaged to different extent by the earthquake, through a performance- basedapproach. The procedure should be valuable as a design tool in all seismic prone area, as it is envisaged for buildings of high strategic importance. In this paper the methodology will beexemplified with reference to steel structures.

THE FIRE FOLLOWING EARTHQUAKE (FFE) HAZARD

• STRUCTURE DAMAGED BY EARTHQUAKE

• COMBINATION OF HUMAN DENSITY, STRUCTURAL CHARACTERISTICS AND METEOROLOGICAL CONDITIONS

• LEAK AND/OR ELECTRIC SHORT-CIRCUIT PRODUCED BY FIRE

• WATER SUPPLY INCREASES DUE TO THE DIFFICULTIES FOR THE FIREMEN IN REACHING THE PLACE FOR CONCOMITANT SEISMIC COLLAPSES OF ROAD NETWORKS AND FAILURE OF THE WATER SYSTEMS

MAIN HISTORICAL RECORDS

Fire after 1923 Tokyo seism(Japan)

Fire after 1994 Northridge seism(USA)

Fire after 1995 Kobe seism(Japan)

Fire after 2009 Pandang seism(Indonesia)

RISK FACTORS

THE CURRENT CODIFICATION APPROACH

METHODOLOGY FOR THE ROBUSTNESS ASSESSMENT OF STRUCTURES UNDER FIRE AFTER EARTHQUAKE

• ABAQUS. 2004b. ABAQUS Standard User’s Manual, Ver.6.5.• CEN 2002. EN 1990, Eurocode. Basis of structural design.• Bianco L. 2006. Effects of the fire on structural material (in Italian). www.buildup.it.• Faggiano B., Esposto M., Mazzolani F.M. 2008a. Risk assessment of steel structures under fire following earthquake, 14th World Conference on Earthquake Engineering, Beijing, PRC, 12-17 October, No. S19-015.• Faggiano B., Esposto M., Mazzolani F.M., Landolfo R. 2007. Fire analysis on steel portal frames damaged after earthquake according to performance based design. Workshop in Prague Urban Habitat Constructions under catastrophic events,

COST-Action C26, Prague, Czech Republic, March 2007, F. Wald, F.M. Mazzolani, M. Byfield, D. Dubina, M. Faber (Eds.), Print Prazska technica, ISBN: 978-80-01-03583-2, pp. 35-40.• ISO/TR 13387. 1999. Fire safety engineering.• Purkiss J.A. 2007. Fire safety engineering. Design of structures. Butterworth-Heinemann, Elsevier. ISBN-13: 978-0-7506-6443-1.

REFERENCES

EARTHQUAKE

1971 California(USA)

1994 Kobe(Japan)

1995 Northridge(USA)

2009 L’Aquila(Italy)

FIRE

TRADITIONAL APPROACH of deterministic type(Eurocodes)

MODERN APPROACH of performance type(FSE: Fire Safety Engineering, ISO/TR 13387, 1999)

PERFORMANCE BASED DESIGN (FEMA 356, November 2000)

OPERATIONAL

(O)

IMMEDIATE OCCUPANCY(IO)

LIFE SAFE

(LS)

COLLAPSE PREVENTION

(CP)

Very Light overall damage: the post-earthquake damage state in which the structural and non-structural components are able to support the pre-earthquake functions present in the building.

Light overall damage: the post-earthquake damage state guaranteeing the structure to remain safe to be occupied and to essentially retain the pre-earthquake design strength and stiffness.

Moderate overall damage: the post-earthquake damage state related to structural components, guaranteeing the structure to retain a safety margin against onset of partial or total collapse.

Severe overall damage: the post-earthquake damage state related to structural components, guaranteeing that the structure continues to support gravity loads but retains no safety margin against collapse.

• Unified approach for all the buildings categories

• Fire action modelled through the nominal curves• Simulations able to define different functions of

state for the fire phenomenon

• Finite Element structural analyses

• Possibility to investigate and to reduce the lossof life and damage to property,

• Possibility to quantify the risks and the hazardsinvolved and provide an optimal solution to theapplication of preventive or protective measures(Purkiss, 2007)

• IDENTIFICATION OF THE SEISMIC DAMAGE STATE, ACCORDING TO THEPRE-FIXED SEISMIC PERFORMANCE LEVELS, IN RELATION TO THEINTENSITY OF THE EVENT

• DETERMINATION OF THE RESIDUAL BEARING CAPABILITIES OF THESEISMIC DAMAGED STRUCTURES SUBJECTED TO FIRE, ACCORDING TOPRE-FIXED FIRE PERFORMANCE LEVELS, IN RELATION TO THE FIREEVENT.

OPERATIONAL Fire(Of)

IMMEDIATE OCCUPANCY fire(IOf)

LIFE SAFE Fire(LSf)

COLLAPSE PREVENTION fire(CPf)

Very Light overall damage. It shall be defined as the fire damage state in which the structural and non-structural components are able to support the pre-event functions present in the building.

Light overall damage. It shall be defined as the fire damage state that preserves equipments and contents and guarantees the structure to remain safe to be occupied.

Moderate overall damage. It shall be defined as the fire damage state that guarantees the structure to retain a safety margin against onset of partial or total collapse, while architectural, mechanical and electrical systems are damaged.

Severe overall damage. It shall be defined as the fire damage state that allows the structure to support gravity loads, without retaining a safety margin against collapse; while extensive damage to the non structural components are present.

METHODOLOGY

The methodology is the application of a performance-based approachinspired from the FEMA 356 Guidelines and the philosophy of the FSE

FIRE PERFORMACE LEVELS

SEISMIC PERFORMANCE LEVELS

CASE STUDY

FIRE LOCATION

SEISMIC PERFORMANCE LEVELS (FEMA 356, 2000)

FFE PERFORMANCE

IO LS CP1 CP2

Of 387 0 0 0

LSf 1382 0 0 0

CSf 1451 1446 1418 938

CLf 1587 1574 1544 1168

CGf 3076 2788 2340 1892

Operational fire(Of)

Life Safe fire(LSf)

Section Collapse fire(CSf)

Local Collapse fire(CLf)

Global Collapse fire(CGf)

S

Attainment of the yield stress in the most stressed section

Formation of the first plastic hinge

Failure of the cross-section

Beam mechanism

Global mechanism

NS

Negligible damage

Equipments,contents are secure

Architectural, mechanical electrical systems damaged

Extensive damage

(S= Structural components; NS= Non structural components)

RESISTANCE [s]

FIRE PERFORMACE LEVELS

STEEL FRAME GEOMETRY [m]

0

200

400

600

800

0,0% 1,0% 2,0% 3,0% 4,0% 5,0% 6,0% 7,0% 8,0% 9,0%

V [kN]

d/h [%]

IO

LS

CP1 CP2

PG

A=

0.99

PG

A=

1.18

PG

A=

1.26

PG

A=

1.25

O

MAIN PHASES

OfCL

f

CG

f 0

500

1000

1500

2000

2500

3000

3500

IO2

CP

1_

2

Performance Fire Levels

Resistance [s]

Performance Seismic Levels

IO2 LS2 CP1_2 CP2_2

Of 387 0 0 0

LSf 1382 0 0 0

CLf 1451 1446 1418 938

CSf 1587 1574 1544 1168

CGf 3076 2788 2340 1892

PERFORMANCE LEVELS (case d)

LS CP1IO SEISMIC PERFORMANCE

LEVEL

FIRE PERFORMANCE LEVEL