Lezione Sicurezza Strutturale Antincendio Costruzioni Metalliche 17 oct 2013

Luisa GiulianiAssistant Professor, Ph.D., P.E.

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DTU ‐ BYGCivil Engineering Department

Technical University of DenmarkFire sa

fety design of steel structures


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Technical University of Denmark

FIRE SAFETY AT DTU‐BYG


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DTU‐BYG


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FIRE GROUP AT DTU‐BYG


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FIRE GROUP AT DTU‐BYG

Luisa GiulianiAssistant Professor

Structural fire safety

Anne DederichsAssociate Professor

Toxicity and evacuation

Aldis LarusdottirPh.D. student

Evacuation of children

Grunde JomaasAssociate Professor

Flame spread

Kristian HertzFull Professor

Fire Safety Design, Concrete Structures

Annemarie PoulsenExternal lector

Design fire and regulation

Ludmilla RozanovaPost Doc

Evacuation

Annemarie PoulsenPh.D. student

Evacuation of disabled people


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Group competences

KHZ AND GRUJO ALLARAMPLUGI JAGS


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Civil Engineering education (M.Sc.):11020 Building Fire Safety11022 Fire Dynamics11023 Structural Fire Safety

FIRE SAFETY EDUCATION AT DTU

11020 Building Fire Safety

11022 Fire Dynamics

11023 Structural Fire Safety

Special courses

Thesis projects


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1. Structural fire safety of car parks

2. Thermal resistance of intumescent paints

PERSPECTIVE EXCHANGE STUDENT

3. Fire induced collapse of steel structures

4. Effect of SSI on ship collision with OWT

Available thesis projects on steel structures

DTU SAPIENZA ‐ ERASMUS PROGRAM 2014/15



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0. Semester – Efterår 201011E16 Ingeniørmæssig matematik og

fysik for Bygningskonstruktører

1. Semester – Forår 201111B12 Brandmodellering 1 11B01 Konstruktionsbrandteknik 11B11 Miljøkemi

2. Semester – Efterår 201111B25 Branddynamik 11B04 Brandkemi11B24 Bygningsbrandteknik

3. Semester – Forår 201211B02 Risikovurdering i kemisk industri eller11B03 Risikostyring (valgfrit) 11B13 Brandteknisk dimensionering11B26 Brandmodellering 2 ‐ eller11B27 Komplekse bygninger (valgfrit)

4. Semester – Efterår 201211B17 Brandteknisk projektopgave

Satellitkursus11B28 Modellering af bygninger ved brand 11B29 Installationer


Master in Fire Safety (MiB):http://www.byg.dtu.dk/Uddannelse/Masteruddannelse/Brandsikkerhed.aspx


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FIRE SAFETY DAY

Yearly event ‐ Next FSD 12 June 2014


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FIRE SAFETY DESIGN OF STEEL STRUCTURES


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I. Motivation and strategies: Fire cases, fire phases and fire design strategies (active and passive measures)

II. Approaches and methodology: Design approaches and design steps for structural fire safety

IV. Problems: Effects of thermal expansion and large displacements on collapse modes


Luisa Giuliani ‐ Fire safety design of steel structures

Motivation

Prob

lems

Approa

ch and

metho

dology

Højbro Plads, Christiansborg fire 1884

http://indenforvoldene.dk/hoejbro%20plads.html

Development of fire safety design in Scandinavia


Motivation

Prob

lems

Approa

ch and

metho

dology

Firestorms

DARMSTADT, 1944 DRESDEN, 1945


Motivation

Prob

lems

Approa

ch and

metho

dology

Firewalls and errors

HAZARD

IN-D

EPTH D

EFENCE

HOLES DUE TOACTIVE ERRORS

HOLES DUE TOHIDDEN ERRORS

Usage & maintenance

Fire detection

Fire suppression

Fire resistance

Collapse resistancePASSIVE

ACTIVE

ALIVE

Structural characteristics

The Swiss cheese model


Motivation

Prob

lems

Approa

ch and

metho

dology

robustness

Y

N collapse

activeprotectio

n

passiveprotection

no failures

doesn’t trigger

Y

N

Y

N

spreads

extinguishes

damages

Y

N

no collapse

triggers

prevention

1 42 3

Fire safety strategies


Motivation

Prob

lems

Approa

ch and

metho

dology

Mandarin oriental hotel, Beijing 2009Built: under construction Height: 44 floors, 158 mUse: hotel, not occupied yetStructure: steel‐framed with concrete coreFire: triggered at roof, spread downwardsCause: unauthorized fireworkDuration: 5 hoursInjuries: 1 casualty (fireman), 7 injuriesDamages: many floors, no frame, ca. $100mil

Examples of accidental fires


Motivation

Prob

lems

Approa

ch and

metho

dology

Tamweel Towers , Dubai 2012Built: 2009 ‐ faulty sprinklersHeight: 35 storeyUse: office and apartmentsStructure: concrete, alum. & fiberglass cladd.Fire: spread due to flammable claddingCause: cigarette butt thrown in a pile of

waste materials left on a balconyInjuries: none, but 61 cars from debris!

Examples of accidental fire


Motivation

Prob

lems

Approa

ch and

metho

dology

robustness

Y

N collapse

activeprotectio

n

passiveprotection

no failures

doesn’t trigger

Y

N

Y

N

spreads

extinguishes

damages

Y

N

no collapse

triggers

prevention

1 42 3



Motivation

Prob

lems

Approa

ch and

metho

dology

First Interstate Bank, Los Angeles 1988Built: 1973, sprinkler systemHeight: 62 floorsUse: office and publicStructure: protected steel Fire: triggered at 12th, vertical spread i4 floors Cause: electrical? – sprinklers not fully activeDuration: 3 and ½ hoursInjuries: 1 casualty, 49 injuriesDamages: not in main structural members, $50 mil.

Example of fire spread


Motivation

Prob

lems

Approa

ch and

metho

dology

Grozny Building, Cechnya 2013Built: 2011 (SPRINKLER?)Height: 140 m ‐ 40 story

303 m ‐ 65Use: hotel and apartmentsFire: spread due to combustible part

of insulationCause: short circuit / human errorDuration: 8 hoursInjuries: none (not occupied)Damages: only façade, interior untouched

Example of fire spread


Motivation

Prob

lems

Approa

ch and

metho

dology

robustness

Y

N collapse

activeprotectio

n

passiveprotection

no failures

doesn’t trigger

Y

N

Y

N

spreads

extinguishes

damages

Y

N

no collapse

triggers

prevention

1 42 3



Motivation

Prob

lems

Approa

ch and

metho

dology

www.davidicke.com/forum/showthread.php?t=85545

STILL STANDING!

Example of fire induced damages

Andraus Building ‐ Sao Paulo, 1972Andraus Building, Sao Paulo 1972Built: 1962Height: 15 m, 32 floors – no sprinklerUse: officesStructure: concrete frame and wallsFire: started at 3rd floor ‐ spread to 27th

in 25 min – due to open stairs and plywood in slab formwork

Cause: electrical system overload (?) Injuries: 16 casualties (jumpers), 330 inj.


Motivation

Prob

lems

Approa

ch and

metho

dology

Example of fire induced damages

www.davidicke.com/forum/showthread.php?t=85545

STILL STANDING!

Joelma Building ‐ Sao Paulo, 1974

Fire Disasters ‐ CookeOnFire.comwww.cookeonfire.com/pdfs/Joelma.pdf

Joelma Building, Sao Paulo 1974Built: 1972 ‐ no sprinklerHeight: 25 floorsStructure: R.C. concrete, banking companyFire: triggered ta 12th floor – spread

upwards due to flammable interiors

Duration: 4 h and 30 minCause: short circuit Injuries: 180‐190

casualties (40 jumpers)

www.hispanicallyspeakingnews.com/latin‐american‐history/details/


Motivation

Prob

lems

Approa

ch and

metho

dology

robustness

Y

N collapse

activeprotectio

n

passiveprotection

no failures

doesn’t trigger

Y

N

Y

N

spreads

extinguishes

damages

Y

N

no collapse

triggers

prevention

1 42 3



Motivation

Prob

lems

Approa

ch and

metho

dology

Examples of fire induced collapses

Windsor Tower, Madrid 2005Built: 1979, fire prot. under constructionHeight: 106 m, 32 floorsUse: office buildingStructure: concrete core and steel columnsFire: triggered at 21st, vertical spreadCause: short‐circuit/arson? ‐ partial insulationDuration: 24 hoursInjuries: 7 firemen, no casualtiesDamages collapse of upper part, collapse standstill!


Motivation

Prob

lems

Approa

ch and

metho

dology

Technical University, Delft 2008Built: ‘70enties, no sprinkler systemHeight: 13 floorsUse: office buildingStructure: concreteFire: triggered at 6th floor, spread

upwards Cause: coffee machine short circuitDuration: 7 hoursInjuries: no, thanks to rapid evacuationDamages: major collapse of northern wing,

only vertical propagation

Examples of fire induced collapses


Motivation

Prob

lems

Approa

ch and

metho

dology

Firedevelopment

Evacuationand rescue

Structuralbehavior

Compartmentmentaliz.

PC susceptibilityEscape/access routes

SAFETY OFPEOPLE

STRUCTURAL INTEGRITY

Safety of people and properties


Motivation

Prob

lems

Approa

ch and

metho

dology

passive

Create fire compartments

Prevent damage in the elements

Prevent loss of functionality in the building

Structure

Fire Safety Strategies

active

Detection measures(smoke, heat, flame detectors)

Suppression measures (sprinklers, fire extinguisher, standpipes, firemen)

Smoke and heat evacuation system

prevention protection robustness

Limit ignitionsources

Limit hazardous human behavior

Emergency procedure and evacuation

Prevent the propagation of collapse, once local damages occurred (e.g. redundancy)

People



Motivation

Prob

lems

Approa

ch and

metho

dology

A) when heat source comes in contact to a combustible material

B) when it involves adjacent materials

C) when all materials participate to combustion

D) when the maximum temperature is reached

PROPAGATION GROWTH PHASE

FLASHOVER FULLY DEVELOPED PHASE

Q

Structural fire

IGNITION INCIPIENT PHASE

PEAK EXTINCTION PHASEA

TRANSITIONFROM CONTENT

TO STRUCTURAL FIRE


Motivation

Prob

lems

Approa

ch and

metho

dology

Flashoverceiling jet

rollover

flashover

STRUCTUREFIRE

CONTENTFIRE


Motivation

Prob

lems

Approa

ch and

metho

dology

NIST ‐ Flashover Room Fires

Ceiling jet, rollover, flashover: total time 45 seconds

http://www.youtube.com/watch?v=QqMVm72FMRk

Flashover


Motivation

Prob

lems

Approa

ch and

metho

dology

FlashoverDefinition:‐ flashover occurs when the entire room contents ignite simultaneously

Criterion:‐ Babrauskas criterion: 600°C and 20kW/m2

UPPER AND LOWER LAYER

(TWO‐ZONES MODEL)

PRE‐FLASHOVER POST‐FLASHOVER

Design fires

SAME TEMPERATURE IN THE WHOLE COMPARTMENT

(ONE ZONE MODEL)


Motivation

Prob

lems

Approa

ch and

metho

dology

Post‐flashover phases

PRE‐FLASHOVER POST‐FLASHOVER

Post‐flashover models

DESIGNmonotonically increasing

PARAMETRICwith cooling phase

DECAY:fire temperature decreases –NOT structure temperature!

analyticalmodels

fire tests(conventional)


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I. Motivation: Fire cases, fire phases and fire design strategies (active and passive measures)




Motivation

Prob

lems

Approa

ch and

metho

dology

Design approaches

Structural fire safety

b. against failure c. against collapsea. for time resistance

a. RESISTANCE CLASS b. FULLY DEVELOPED FIRE

verifications for all durationof a compartment fire

(parametric fire – hand calculations)

BUILDING RESPONSE

verifications ofconventional collapse

for different fire scenarios

(PB! Often natural fire – FEM)

Structural behaviour afterdesign time is unknown

Integrity of the structure

verifications for alimited time of standard fire

(nominal fire ‐ hand calculations)

WELL‐ESTABLISHED PROCEDURE ADVANCED DESIGN

design

complexity

knowledge

b. FULLY DEVELOPED FIRE c. BUILDING RESPONSE


Motivation

Prob

lems

Approa

ch and

metho

dology

2

Design methodology

modeling of fire action1

heat transmission 2

material properties3

structural behaviour4

1

Fire design processFIRE ACTION

FIRE COURSE

1

ELEMENT TEMPERATURE

2

MATERIAL DEGRADATION

3

VERIFICATIONOR DESIGN

4

Ponticelli&Caciolai, 2008

RESISTAN

CESTIFFN

ESS

3


Motivation

Prob

lems

Approa

ch and

metho

dology

DESIGN APPROACH

METHODOLOGYa. Resist. class b. Fully developed fire c. PBFD

1. Fire curveNominal Parametric Natural

Standard EN DS SW CFD

2. Heating curve Expression for protected/unprotected steel Heat transfer

3. Material behavior Effective yielding Proof stress Realistic

4. Verification

Safetycoeff.

Mat. Charact. Charact. Design Design Realistic

Load Greater reduction Lower reduction Effective

Check level Section Section Section Element Structure

Check type Time of resistance Resist. Tcritical Res./Displ. Conventional

collapse

Structural fire safety: methodology


Motivation

Prob

lems

Approa

ch and

metho

dology

Structural fire design: main steps


1


FIRE COURSE

1



Motivation

Prob

lems

Approa

ch and

metho

dology

medium‐sizeoffices DK NL LUX FR UK

‐‐ R60 R90 R120 R120

R90 R90 R120 R120 no

Time [min]

STANDARD FIRE CURVE

resistance classes givenfor type of usage

Ysprinkler

N

0

200

400

600

800

1000

1200

0 20 40 60 80 100 120

R60 945 ̊CR30 842 ̊CR15 739 ̊C R60 945 ̊CR30 842 ̊CR15 739 ̊C R90 1006 ̊C R120 1049 ̊C

1a. Fire action: standard curve


Motivation

Prob

lems

Approa

ch and

metho

dology

1b. Fire action: parametric curves

SW parametric EN parametricDS parametricPARAMETRIC FIRES

0

200

400

600

800

1000

1200

0 10 20 30 40 50 60 70 80 90

Tempe

rature ‐ Fire load

‐ Fire growth rate

FUEL

‐ Opening factor‐ Thermal inertia

COMPARTMENT

Properties of the


Motivation

Prob

lems

Approa

ch and

metho

dology

1c. Fire action: natural curves

Initial phase: fire affected by combustible type

Final phase: cooling due to combustible exhaustion

Central phase: fire controlled by ventilation


Motivation

Prob

lems

Approa

ch and

metho

dology

2



heat transmission 2

1


FIRE COURSE

1

ELEMENT TEMPERATURE

2



Motivation

Prob

lems

Approa

ch and

metho

dology

2a. Steel heating curve: monotonic

0

200

400

600

800

1000

1200

0 10 20 30 40 50 60 70 80 90 100 110 120

UNINSULATED STEEL

INSULATED STEEL

Critical temperature

UNIFORM TEMPERATURE DISTRIBUTION ASSUMED!

t )T - (T VF

c T T 1-i

s*

gs

s1-i

sp,s

*1-i

si

s


Motivation

Prob

lems

Approa

ch and

metho

dology

2b. Steel heating curve: cooling phase

0

200

400

600

800

1000

1200

0 10 20 30 40 50 60 70 80 90

Critical temperature

UNIFORM TEMPERATURE DISTRIBUTION ASSUMED!

t )T - (T VF

c T T 1-i

s*

gs

s1-i

sp,s

*1-i

si

s


Motivation

Prob

lems

Approa

ch and

metho

dology

2c. Advanced heat transfer

‐ to the element surface(thermal map from CFD code)

‐ into element sections(heat transfer in 2D FEs)

‐ along structural elements(heat transfer analysis)

THERMAL ANALYSIS

TEMPERATURE EVOLUTION


Motivation

Prob

lems

Approa

ch and

metho

dology

Heat transfer problem

conduction

conduction

Ts (x,t)Toradiation

T1 (t)

ABSORBED BY WALLS

EXCHANGEDBY AIR FLOW

RADIATED THROUGH OPENINGS

Tg (t)convection


Motivation

Prob

lems

Approa

ch and

metho

dology

Heat transfer problem for steel

conduction

radiation

T1 (t)

ABSORBED BY WALLS

EXCHANGEDBY AIR FLOW

RADIATED THROUGH OPENINGS

Tg (t)convection

To

Ts (x, t)

Ts (t) = T1

s (t) = 30 W/(m K)


Motivation

Prob

lems

Approa

ch and

metho

dology

Heating curve of uninsulated steel

Tg (t)

To

Ts (t)

Ts (t)

convection

radiation

Tg ‐ Ts

ΔT V c ρ Δt )T ‐ (T F α ssp,sssgs

Δt )T ‐ (T VF

c ρα

ΔT sgs

s

p,sss

NUMERICAL SOLUTION

Ts = Ts (Ts)

= (Ts)

cp,s = cp,s (Ts)

ΔU ΔQ

increment of internal energy [J]heat ceased in a time interval [J]


Motivation

Prob

lems

Approa

ch and

metho

dology

Insulated steelINTUMESCENT PAINT

after fire


before fire


Motivation

Prob

lems

Approa

ch and

metho

dology

Thermal resistance of the insulation

VARIES WITH THE TEMPERATURE!!

To

Ts (t)

Ts (t)

Tg (t) Tin (t)

conduction

THICKNESS OF INTUMESCENT PAINT VARIES TOO…

din(t)

high expansion intumescentbefore and after furnace heating

MSc PROJECTAT DTU!

CONDUCTIVITY VARIES WITH TEMPERATURE…

Insulated steel

TR = din / in [m2 K / W]

insulation conductivity [W/(m K)]

insulation thickness [m]

in in (Tin (x, t)) in in (Tin (t))din = thin


Motivation

Prob

lems

Approa

ch and

metho

dology

2


modeling of fire action1 material properties3

1


FIRE COURSE

1

ELEMENT TEMPERATURE

2


3


RESISTAN

CESTIFFN

ESS

3


Motivation

Prob

lems

Approa

ch and

metho

dology

Steel mechanical properties degradation

T

<=100°C200°C

400°C

600°C

800°C

500°C

EC 1‐2

2%

20%0.2% 15%

sw B52

fyk

STIFFNESS, ELASTIC LIMIT, RESISTANCE


Motivation

Prob

lems

Approa

ch and

metho

dology

fyT

500°C

2%

20%15%

fpT

p

20°Cfy

E

ET

Degradation of stiffness and resistance

2% stress considered for yielding

3a. Material behavior: steel degradation


Motivation

Prob

lems

Approa

ch and

metho

dology

500°C

20%0.2%

15%

f0.2T

fpT

p

20°Cfy

E

ET


0.2% proof stress considered for yielding

3b. Material behavior: steel degradation


Motivation

Prob

lems

Approa

ch and

metho

dology

3. Material behavior: steel degradation

0

0,2

0,4

0,6

0,8

1

1,2

0 100 200 300 400 500 600

Resistance

Stiffness

0

0,2

0,4

0,6

0,8

1

1,2

0 200 400 600 800 1000 1200

Resistance

Stiffness

1) EUROCODES 2) SWEDISH METHODNATIONAL DANISH ANNEX

2.0% effective yield stress 0.2% proof stressRESISTANCE


Motivation

Prob

lems

Approa

ch and

metho

dology


Elastic‐perfectly plastic with hardening

500°C

20%u

fuT

fpT

p

20°Cfy

E

ET

3c. Material behavior: steel degradation


Motivation

Prob

lems

Approa

ch and

metho

dology

2



heat transmission 2

material properties3

structural behaviour4

1


FIRE COURSE

1

ELEMENT TEMPERATURE

2


3

VERIFICATIONOR DESIGN

4


RESISTAN

CESTIFFN

ESS

3


Motivation

Prob

lems

Approa

ch and

metho

dology

5% fractile

of 0.2% proof stress

charact. value

fyd = fyk / γm

γm = 1.0

medium value

fyd = fym / γm

γm = 1.0

most probable yielding resistance

+ hardening!

b. FULLY DEVELOPED c. PBFD

charact. value

fyd = fyk / γm

γm = 1.0

a. RESISTANCE CLASSES

5% fractile

of 2.0% effective yield stress

4. Verification: material safety coefficients


Motivation

Prob

lems

Approa

ch and

metho

dology

4. Verification: load safety coefficients

Ultimate Limits state (ULS)

Accidental Limit State (ALS)

LOAD COEFF. Gk Qk1 Qki Gk Qk1 Qki

EUROCODE 1.35 1.50 1.5∙0.7 1.00 0.60 0.20

DANISHSTANDARD

1.00 1.30 0.50 1.00 1.00 0.50

Ultimate Limits state (ULS)

Accidental Limit State (ALS) ALS/ULS

EUROCODE 8.49 kN/m2 4.55 kN/m2 0.54

DANISHSTANDARD

7.15 kN/m2 6.25 kN/m2 0.87

SAFETYCOEFFICIENTS

EXAMPLE OFFLOOR LOAD

DS: conservativeALS loads

EN: conservativeULS loads


Motivation

Prob

lems

Approa

ch and

metho

dology

4. Verification: collapse criterion

severity

complexity

STRUCTUREPBFD (displacement limits)

max < L/20

max < L2 / 800 H

SECTION ULSALS (Eurocodes)

Mu

ELEMENTALS(Swedish method)

Pu

FIBERSLS(+ deform. check)

y

LEVEL OF VERIFICATION


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I. Motivation and strategies: Fire cases, fire phases and fire design strategies (active and passive measures)


IV. Problems: Effects of thermal expansion and large displacements on collapse modes



Motivation

Prob

lems

Approa

ch and

metho

dology

Structural analysis issues

THERMAL EXPANSION

INDIRECT STRESSES

THERMAL EFFECTSA

LARGE DISPLACEMETSB

COLLAPSE CRITERIONC


Motivation

Prob

lems

Approa

ch and

metho

dology

A. Thermal expansion

relative thermal elongation (L/L0 ) = ∙ T [ad.]

therm = (T) ∙ T [ad.]


Motivation

Prob

lems

Approa

ch and

metho

dology


relative thermal elongation

Ltherm/L = (T) ∙ T [ad.]

thermal expansion coefficient [K‐1]

Total deformation: tot = therm(T) + mech(,T)

not hindered hindered

elongation+

induced deformation

partially hindered

elongation and compression+

induced deformation and stresses

eigenstresses

eigen(T, ET) Ltherm(T)

eigen = kET E20 Lfree /L

compression+

induced stresses

RESTRAIN GRADE


Motivation

Prob

lems

Approa

ch and

metho

dology


Total deformation: tot = therm(T) + mech(,T)

hindered

eigenstresses

eigen(T, ET) Ltherm(T)

eigen = kET E20 Lfree /L

compression+

induced stresses

relative thermal elongation

Ltherm/L = (T) ∙ T [ad.]

thermal expansion coefficient [K‐1]

not hindered

elongation+

induced deformation

partially hindered

elongation and compression+

induced deformation and stresses

Lreal = ∙ lfree

eigen = kET E20 (1 ‐ ∙ Lfree /L

RESTRAIN GRADE


Motivation

Prob

lems

Approa

ch and

metho

dology

A. Indirect stresses

LC hind

N

LB,real

N + N

LC

a b

LB

ΔLΔL

ΔLhinderedrealized

realized

restrain

coefficient free

realized

ΔLΔL

γ

KΔN

ΔL TflexB,

realized T

C,ax

hindered

KΔN

ΔL

displacement of the beam displacement of the column

TC,ax

TflexB,

KK1

1γ

hideredtotally 0KK

freetotally 1KK

Tax,C

Tflex,B

Tflex,B

Tax,C


Motivation

Prob

lems

Approa

ch and

metho

dology


0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

0 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,1

K

hinged at both ends clumped at both ends

K4811

γ

K 19211

γ

CCC

3BBB

/LAELIE

K


Motivation

Prob

lems

Approa

ch and

metho

dology

A. Indirect stressesdesign of columnLoad bearing capacity of restrained columns is much lower!!


Motivation

Prob

lems

Approa

ch and

metho

dology


indirect stresses

DISREGARDED

in case standard fire is used

severe fire

verification on single members without effect of adjacent element

CONSIDERED

for buckling verification

verification on single columns,but effect of adjacent element is considered

EC 1‐2sw B52

L

ΔL‐1EΔσ

freeT

eigen

TC,ax

TflexB,

KK1

1γ

0 eigen∆σ ISO834

t

T

L E1

E1

AN

T ΔL 20Tfree


Motivation

Prob

lems

Approa

ch and

metho

dology

THERMAL EXPANSION

INDIRECT STRESSES

BOWING EFFECT

CATENARY/MEMBR. ACTION

possible overloading of elements

higher displacements induced

THERMAL EFFECTSA

LARGE DISPLACEMETSB

COLLAPSE CONDITIONC



Motivation

Prob

lems

Approa

ch and

metho

dology

WHEN DISPLACEMENT ARE LARGE

THESE BEAMS BEHAVE DIFFERENTLY

UNDER VERTICAL LOADS

B. Large displacements

Q

L

horizontally restrained

L

simply supported

1. A vertically loaded simply supported beam is exposed to fire. The sliding support:a. will stay stillb. will move to the right (toward the outside)c. will move to the left (toward the other support)

2. What would happen if the beam were horizontally restrained instead?


Motivation

Prob

lems

Approa

ch and

metho

dology

1. A vertically loaded simply supported beam is exposed to fire. The sliding support:a. will stay stillb. will move to the right (toward the outside)c. will move to the left (toward the other support)

2. What would happen if the beam were horizontally restrained instead?

Q

L

horizontally restrained

L

simply supported

A

N N

first expansionthen contraction

first compressionthen tension



Motivation

Prob

lems

Approa

ch and

metho

dology

simply supported beam horizontally restrained beam

q q

T T

tension catenary actionLD prevails bowing effect2

compression II ord. momentthermal effect prevails expansion1



Motivation

Prob

lems

Approa

ch and

metho

dology

THERMAL EXPANSION

INDIRECT STRESSES

BOWING EFFECT




THERMAL EFFECTSA

LARGE DISPLACEMETSB

COLLAPSE MODEC

LOW RESTRAIN

HIGH RESTRAIN

possible loss of supports

generally beneficial for members



B. Collapse mode: sway collapse of industrial hall

Denmark 2013 Romania 2010

Alexandru Dondera, MSc thesis, 2013


B. Collapse mode: early beam buckling of tall buildings

‐200

‐100

0

100

200

300

400

500

600

700

0 100 200 300 400 500 600 700 800 900 1.000

Axial Force (k

N)

Temperature (°C)

THERMAL BUCKLING

PLASTIC HINGE

TENSILE COLLAPSE

IPE 270HE 1000 M

= 0.9

HIGH RE

STRA

INT

LOW RESTR

AINT

Riccardo Aiuti, MSc thesis, 2013


Motivation

Prob

lems

Approa

ch and

metho

dology

WTC, Usmani&al.2003

B. Collapse mode: vertical propagation


Motivation

Prob

lems

Approa

ch and

metho

dology

THERMAL EXPANSION

INDIRECT STRESSES

BOWING EFFECT




THERMAL EFFECTSA

LARGE DISPLACEMETSB

COLLAPSE MODEC

LOW RESTRAIN

HIGH RESTRAIN

possible loss of supports

generally beneficial for members

Sway collapse

Early buckling, possible PC



[email protected]



fety design of steel structures I. Motivation and strategies:

Explain why structural fire safety is important, and which fire phases are involved,what is flashover and why it allows for one‐zone model assumption in post FO models

II. Approaches and methodology:Name three different design approach for structural fire safety and explain the maindifference in each of the 4 design steps for structural verification and design.

IV. Problems:Explain how mutual stiffness of beams and columns and large displacementsdetermines sway collapse and buckling collapse of steel structures.

LEARNING OBJECTIVES

Lezione Sicurezza Strutturale Antincendio Costruzioni Metalliche 17 oct 2013

Education

Transcript of Lezione Sicurezza Strutturale Antincendio Costruzioni Metalliche 17 oct 2013