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Lezione Sicurezza Strutturale Antincendio Costruzioni Metalliche 17 oct 2013

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Lezione di Progettazione Strutturale Antincendio a Costruzioni Metalliche del 17 ottobre 2013. Facolta' di Ingegneria Civile e Industriale de La Sapienza di Roma.

Lezione di Progettazione Strutturale Antincendio a Costruzioni Metalliche del 17 ottobre 2013. Facolta' di Ingegneria Civile e Industriale de La Sapienza di Roma.

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  • 1. Fire safety design of steel structures FIRE SAFETY AT DTU‐BYG Luisa Giuliani Assistant Professor, Ph.D., P.E. lugi@byg.dtu.dk DTU ‐ BYG Civil Engineering Department Technical University of Denmark
  • 2. Fire safety design of steel structures DTU‐BYG Luisa Giuliani Assistant Professor, Ph.D., P.E. lugi@byg.dtu.dk DTU ‐ BYG Civil Engineering Department Technical University of Denmark
  • 3. Fire safety design of steel structures DTU‐BYG Luisa Giuliani Assistant Professor, Ph.D., P.E. lugi@byg.dtu.dk DTU ‐ BYG Civil Engineering Department Technical University of Denmark
  • 4. Fire safety design of steel structures FIRE GROUP AT DTU‐BYG Luisa Giuliani Assistant Professor, Ph.D., P.E. lugi@byg.dtu.dk DTU ‐ BYG Civil Engineering Department Technical University of Denmark
  • 5. FIRE GROUP AT DTU‐BYG Kristian Hertz Full Professor Fire safety design of steel structures Fire Safety Design, Concrete Structures Grunde Jomaas Associate Professor Anne Dederichs Associate Professor Toxicity and evacuation Luisa Giuliani Assistant Professor Flame spread Structural fire safety Annemarie Poulsen Ludmilla Rozanova External lector Design fire and regulation Annemarie Poulsen Ph.D. student Evacuation of disabled people Luisa Giuliani Assistant Professor, Ph.D., P.E. lugi@byg.dtu.dk Post Doc Evacuation Aldis Larusdottir Ph.D. student Evacuation of children DTU ‐ BYG Civil Engineering Department Technical University of Denmark
  • 6. Fire safety design of steel structures Group competences KHZ Luisa Giuliani Assistant Professor, Ph.D., P.E. lugi@byg.dtu.dk AND GRUJO LUGI AMP ALLAR JAGS DTU ‐ BYG Civil Engineering Department Technical University of Denmark
  • 7. FIRE SAFETY EDUCATION AT DTU Fire safety design of steel structures Civil Engineering education (M.Sc.): 11020 Building Fire Safety 11022 Fire Dynamics 11023 Structural Fire Safety 11020 Building Fire Safety 11022 Fire Dynamics Special courses Thesis projects 11023 Structural Fire Safety Luisa Giuliani Assistant Professor, Ph.D., P.E. lugi@byg.dtu.dk DTU ‐ BYG Civil Engineering Department Technical University of Denmark
  • 8. FIRE SAFETY EDUCATION AT DTU Fire safety design of steel structures PERSPECTIVE EXCHANGE STUDENT DTU  SAPIENZA  ‐ ERASMUS PROGRAM 2014/15  Available thesis projects on steel structures 1. Structural fire safety of car parks 3. Fire induced collapse of steel structures 2. Thermal resistance of intumescent paints 4. Effect of SSI on ship collision with OWT Luisa Giuliani Assistant Professor, Ph.D., P.E. lugi@byg.dtu.dk DTU ‐ BYG Civil Engineering Department Technical University of Denmark
  • 9. FIRE SAFETY EDUCATION AT DTU Fire safety design of steel structures http://www.byg.dtu.dk/Uddannelse/Masteruddannelse/Brandsikkerhed.aspx Master in Fire Safety (MiB): 0. Semester – Efterår 2010 11E16 Ingeniørmæssig matematik og  fysik for Bygningskonstruktører 1. Semester – Forår 2011 11B12 Brandmodellering 1  11B01 Konstruktionsbrandteknik  11B11 Miljøkemi  2. Semester – Efterår 2011 11B25 Branddynamik  11B04 Brandkemi 11B24 Bygningsbrandteknik  Luisa Giuliani Assistant Professor, Ph.D., P.E. lugi@byg.dtu.dk 3. Semester – Forår 2012 11B02 Risikovurdering i kemisk industri eller 11B03 Risikostyring (valgfrit)  11B13 Brandteknisk dimensionering 11B26 Brandmodellering 2 ‐ eller 11B27 Komplekse bygninger (valgfrit)  4. Semester – Efterår 2012 11B17 Brandteknisk projektopgave Satellitkursus 11B28 Modellering af bygninger ved brand  11B29 Installationer DTU ‐ BYG Civil Engineering Department Technical University of Denmark
  • 10. FIRE SAFETY DAY Fire safety design of steel structures Yearly event    ‐ Next FSD 12 June 2014 Luisa Giuliani Assistant Professor, Ph.D., P.E. lugi@byg.dtu.dk DTU ‐ BYG Civil Engineering Department Technical University of Denmark
  • 11. Fire safety design of steel structures FIRE SAFETY DESIGN OF STEEL STRUCTURES Luisa Giuliani Assistant Professor, Ph.D., P.E. lugi@byg.dtu.dk DTU ‐ BYG Civil Engineering Department Technical University of Denmark
  • 12. Fire safety design of steel structures FIRE SAFETY DESIGN OF STEEL STRUCTURES 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 Assistant Professor, Ph.D., P.E. lugi@byg.dtu.dk DTU ‐ BYG Civil Engineering Department Technical University of Denmark
  • 13. Motivation Development of fire safety design in Scandinavia Problems Approach and methodology Højbro Plads, Christiansborg fire 1884 http://indenforvoldene.dk/hoejbro%20plads.html Luisa Giuliani     ‐ Fire safety design of steel structures
  • 14. DARMSTADT, 1944 DRESDEN, 1945 Problems Approach and methodology Motivation Firestorms Luisa Giuliani     ‐ Fire safety design of steel structures
  • 15. Firewalls and errors HAZARD ALIVE Usage & maintenance Fire detection ACTIVE PASSIVE HOLES DUE TO ACTIVE ERRORS Fire suppression Fire resistance DE FE NC E Collapse resistance -D EP T IN Problems H Approach and methodology Motivation The Swiss cheese model Structural characteristics Luisa Giuliani     ‐ Fire safety design of steel structures HOLES DUE TO HIDDEN ERRORS
  • 16. 1 2 3 4 prevention N doesn’t  trigger Y Y triggers extinguishe s active protectio n N spreads no  failures Y passive protection no collapse Y N Problems Approach and methodology Motivation Fire safety strategies damages robustness N Luisa Giuliani     ‐ Fire safety design of steel structures collapse
  • 17. Approach and methodology Motivation Examples of accidental fires Mandarin oriental hotel, Beijing 2009 Problems Built: Height: Use: Structure: Fire: Cause: Duration: Injuries: Damages: Luisa Giuliani     ‐ under construction  44 floors, 158 m hotel, not occupied yet steel‐framed with concrete core triggered at roof, spread downwards unauthorized firework 5 hours 1 casualty (fireman), 7 injuries many floors, no frame,  ca. $100mil Fire safety design of steel structures
  • 18. Motivation Examples of accidental fire Tamweel Towers , Dubai 2012 Approach and methodology Built: Height: Use: Structure: Fire: Cause: Problems Injuries: 2009 ‐ faulty sprinklers 35 storey office and apartments concrete, alum. & fiberglass cladd. spread due to flammable cladding cigarette butt thrown in a pile of  waste materials left on a balcony none, but 61 cars from debris! Luisa Giuliani     ‐ Fire safety design of steel structures
  • 19. 1 2 3 4 prevention N doesn’t  trigger Y Y triggers extinguishe s active protectio n N spreads Problems Approach and methodology Motivation Fire safety strategies no  failures Y passive protection no collapse Y N damages robustness N Luisa Giuliani     ‐ Fire safety design of steel structures collapse
  • 20. First Interstate Bank, Los Angeles 1988 Built: Height: Use: Structure: Fire: Cause: Duration:  Injuries: Damages: 1973, sprinkler system 62 floors office and public protected steel  triggered at 12th, vertical spread i4 floors  electrical? – sprinklers not fully active 3 and ½ hours 1 casualty, 49 injuries not in main structural members, $50 mil. Problems Approach and methodology Motivation Example of fire spread Luisa Giuliani     ‐ Fire safety design of steel structures
  • 21. Motivation Example of fire spread Grozny Building, Cechnya 2013 2011 (SPRINKLER?) 140 m ‐ 40 story 303 m ‐ 65 Use: hotel and apartments Fire: spread due to combustible part  of insulation Cause: short circuit / human error Duration: 8 hours Injuries: none (not occupied) Damages: only façade, interior untouched Problems Approach and methodology Built: Height: Luisa Giuliani     ‐ Fire safety design of steel structures
  • 22. 1 2 3 4 prevention N doesn’t  trigger Y Y triggers extinguishe s active protectio n N spreads no  failures Y passive protection no collapse Y N Problems Approach and methodology Motivation Fire safety strategies damages robustness N Luisa Giuliani     ‐ Fire safety design of steel structures collapse
  • 23. Andraus Building, Sao Paulo 1972 Built: Height: Use: Structure: Fire: Cause: Injuries: 1962 15 m, 32 floors – no sprinkler offices concrete frame and walls started at 3rd floor ‐ spread to 27th in 25 min – due to open stairs   and  plywood in slab formwork electrical system overload (?)  16 casualties (jumpers),  330 inj. Problems Approach and methodology Motivation Example of fire induced damages www.davidicke.com/forum Andraus Building ‐ Sao Paulo, 1972 /showthread.php?t=85545 STILL STANDING! Luisa Giuliani     ‐ Fire safety design of steel structures
  • 24. www.davidicke.com/forum/ Joelma Building ‐ Sao Paulo, 1974 showthread.php?t=85545  Problems Approach and methodology Motivation Example of fire induced damages STILL STANDING! Fire Disasters ‐ CookeOnFire.com www.cookeonfire.com/pdfs/Joelma.pdf Luisa Giuliani     ‐ Joelma Building, Sao Paulo 1974 Built: Height: Structure: Fire: 1972 ‐ no sprinkler 25 floors R.C. concrete, banking company triggered ta 12th floor – spread  upwards due to flammable  interiors Duration: 4 h and 30 min Cause: short circuit  Injuries: 180‐190  casualties (40 jumpers) www.hispanicallyspeakingnews.com/latin‐ american‐history/details/ Fire safety design of steel structures
  • 25. 1 2 3 4 prevention N doesn’t  trigger Y Y triggers extinguishe s active protectio n N spreads Problems Approach and methodology Motivation Fire safety strategies no  failures Y passive protection no collapse Y N damages robustness N Luisa Giuliani     ‐ Fire safety design of steel structures collapse
  • 26. Motivation Examples of fire induced collapses Windsor Tower, Madrid 2005 1979, fire prot. under construction 106 m, 32 floors office building concrete core and steel columns triggered at 21st, vertical spread short‐circuit/arson? ‐ partial insulation 24 hours 7 firemen, no casualties collapse of upper part, collapse standstill! Problems Approach and methodology Built: Height: Use: Structure: Fire: Cause: Duration: Injuries: Damages Luisa Giuliani     ‐ Fire safety design of steel structures
  • 27. Technical University, Delft 2008 Built: Height: Use: Structure: Fire: ‘70enties, no sprinkler system 13 floors office building concrete triggered at 6th floor, spread  upwards  Cause: coffee machine short circuit Duration: 7 hours Injuries: no, thanks to rapid evacuation Damages: major collapse of northern wing, only vertical propagation Problems Approach and methodology Motivation Examples of fire induced collapses Luisa Giuliani     ‐ Fire safety design of steel structures
  • 28. Approach and methodology Motivation Safety of people and properties SAFETY OF PEOPLE STRUCTURAL  INTEGRITY Evacuation Structural and rescue behavior Escape/access routes PC susceptibility Fire Problems development Compartmentmentaliz. Luisa Giuliani     ‐ Fire safety design of steel structures
  • 29. Fire Safety Strategies prevention protection robustness Structure People active    Limit ignition sources Limit hazardous  human behavior Emergency  procedure and  evacuation Problems Approach and methodology Motivation Fire safety strategies    Luisa Giuliani     ‐ Detection measures (smoke, heat, flame  detectors) Suppression measures  (sprinklers, fire  extinguisher,  standpipes, firemen) Smoke and heat  evacuation system passive    Create fire  compartments Prevent damage in  the elements Prevent loss of  functionality in the  building Fire safety design of steel structures  Prevent the  propagation of  collapse, once  local damages  occurred (e.g.  redundancy)
  • 30. Q A) when heat source comes in contact to a combustible material IGNITION  INCIPIENT PHASE Approach and methodology Motivation Structural fire B) when it involves adjacent materials PROPAGATION  GROWTH PHASE C) when all materials participate to combustion FLASHOVER   FULLY DEVELOPED PHASE Problems D) when the maximum temperature is reached PEAK  EXTINCTION PHASE A Luisa Giuliani     ‐ Fire safety design of steel structures TRANSITION FROM CONTENT TO STRUCTURAL FIRE
  • 31. Flashover Motivation ceiling jet Problems Approach and methodology rollover STRUCTURE FIRE flashover CONTENT FIRE Luisa Giuliani     ‐ Fire safety design of steel structures
  • 32. Motivation Flashover NIST ‐ Flashover Room Fires Problems Approach and methodology Ceiling jet, rollover, flashover: total time 45 seconds http://www.youtube.com/watch?v=QqMVm72FMRk Luisa Giuliani     ‐ Fire safety design of steel structures
  • 33. Motivation Criterion: Problems Definition: Approach and methodology Flashover ‐ ‐ flashover occurs when the entire room contents ignite simultaneously Babrauskas criterion: 600°C and 20kW/m2 Design fires PRE‐FLASHOVER POST‐FLASHOVER UPPER AND LOWER LAYER SAME TEMPERATURE IN THE  WHOLE COMPARTMENT (TWO‐ZONES MODEL) (ONE ZONE MODEL) Luisa Giuliani     ‐ Fire safety design of steel structures
  • 34. fire tests (conventional) Post‐flashover models DESIGN monotonically increasing analytical models PARAMETRIC with cooling phase PRE‐FLASHOVER POST‐FLASHOVER DECAY: fire temperature decreases – NOT structure temperature! Problems Approach and methodology Motivation Post‐flashover phases Luisa Giuliani     ‐ Fire safety design of steel structures
  • 35. Fire safety design of steel structures FIRE SAFETY DESIGN OF STEEL STRUCTURES I.  Motivation:  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 Luisa Giuliani Assistant Professor, Ph.D., P.E. lugi@byg.dtu.dk DTU ‐ BYG Civil Engineering Department Technical University of Denmark
  • 36. Motivation Design approaches Structural fire safety design Approach and methodology a. for time resistance b. against failure c. against collapse b. FULLY DEVELOPED FIRE c. BUILDING RESPONSE  BUILDING RESPONSE  knowledge complexity a. RESISTANCE CLASS ADVANCED DESIGN WELL‐ESTABLISHED PROCEDURE verifications for all duration of a compartment fire (nominal fire ‐ hand calculations) Problems verifications for a limited time of standard fire verifications of conventional collapse for different fire scenarios (parametric fire – hand calculations) (PB! Often natural fire – FEM) Structural behaviour after design time is unknown Luisa Giuliani     ‐ Integrity of the structure Fire safety design of steel structures
  • 37. Motivation Design methodology Fire design process Ponticelli&Caciolai, 2008 FIRE ACTION 1 Problems Approach and methodology 2 FIRE COURSE 2 3 RESISTANCE STIFFNESS 1 1 modeling of fire action 2 heat transmission     Luisa Giuliani     ‐ 3 4 ELEMENT  TEMPERATURE 3 MATERIAL  DEGRADATION material properties structural behaviour Fire safety design of steel structures 4 VERIFICATION OR DESIGN
  • 38. Motivation Structural fire safety: methodology DESIGN         APPROACH  b. Fully developed fire c. PBFD Nominal METHODOLOGY a. Resist.  class Parametric Natural Approach and methodology 1. Fire curve Standard EN DS SW 2. Heating curve Expression for protected/unprotected steel 3. Material behavior Effective yielding Safety coeff. Mat. Load Charact. Charact. Greater reduction Proof stress Design Design Lower reduction CFD Heat transfer Realistic Realistic Effective Problems 4. Verification Check level Section Section Section Element Structure Check type Time of  resistance Resist. Tcritical Res./Displ. Conventional collapse Luisa Giuliani     ‐ Fire safety design of steel structures
  • 39. Problems Approach and methodology Motivation Structural fire design: main steps Fire design process Ponticelli&Caciolai, 2008 FIRE ACTION 1 FIRE COURSE 1 1 modeling of fire action Luisa Giuliani     ‐ Fire safety design of steel structures
  • 40. Approach and methodology Motivation 1a. Fire action: standard curve medium‐size offices STANDARD FIRE CURVE resistance classes given for type of usage R15 739  ̊C 1200 DK NL LUX FR UK Y ‐‐ R60 R90 R120 R120 N R90 R90 R120 R120 no sprinkler R30 842  ̊C R60 945  ̊C R90 1006  ̊C R120 1049 ̊C 1000 800 600 Problems 400 200 Time [min] 0 0 Luisa Giuliani     ‐ 20 40 60 Fire safety design of steel structures 80 100 120
  • 41. Problems SW parametric PARAMETRIC FIRES DS parametric EN parametric 1200 Properties of the 1000 FUEL COMPARTMENT 800 Temperature Approach and methodology Motivation 1b. Fire action: parametric curves ‐ Opening factor ‐ Thermal inertia ‐ Fire load ‐ Fire growth rate 600 400 200 0 0 Luisa Giuliani     ‐ 10 20 30 40 50 Fire safety design of steel structures 60 70 80 90
  • 42. Problems Approach and methodology Motivation 1c. Fire action: natural curves Initial phase: fire affected by combustible type Luisa Giuliani     ‐ Central phase: fire controlled by ventilation Fire safety design of steel structures Final phase: cooling due to combustible exhaustion
  • 43. Motivation Structural fire design: main steps Fire design process Ponticelli&Caciolai, 2008 FIRE ACTION 1 Problems Approach and methodology 2 FIRE COURSE 2 ELEMENT  TEMPERATURE 1 1 modeling of fire action 2 heat transmission     Luisa Giuliani     ‐ Fire safety design of steel structures
  • 44. Approach and methodology Motivation 2a. Steel heating curve: monotonic UNIFORM TEMPERATURE DISTRIBUTION ASSUMED! 1200 Ts  Ts i i -1  *  s c p, s i -1 Fs * i -1 (Tg - Ts )  t Vs 1000 800 600 Critical temperature 400 UNINSULATED STEEL Problems 200 INSULATED STEEL 0 0 Luisa Giuliani     ‐ 10 20 30 40 50 60 70 Fire safety design of steel structures 80 90 100 110 120
  • 45. Problems Approach and methodology Motivation 2b. Steel heating curve: cooling phase UNIFORM TEMPERATURE DISTRIBUTION ASSUMED! Ts  Ts i 1200 i -1  *  s c p, s i -1 Fs * i -1 (Tg - Ts )  t Vs 1000 800 600 Critical temperature 400 200 0 0 Luisa Giuliani     ‐ 10 20 30 40 50 Fire safety design of steel structures 60 70 80 90
  • 46. Problems Approach and methodology Motivation 2c. Advanced heat transfer TEMPERATURE EVOLUTION ‐ 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 Luisa Giuliani     ‐ Fire safety design of steel structures
  • 47. Motivation Heat transfer problem Problems Approach and methodology Tg (t) EXCHANGED BY AIR FLOW convection conduction T1 (t) RADIATED  THROUGH  OPENINGS ABSORBED  BY WALLS Luisa Giuliani     ‐ Ts (x,t) radiation Fire safety design of steel structures conduction To
  • 48. Motivation Heat transfer problem for steel s (t) = 30 W/(m K) Problems Approach and methodology Tg (t) convection EXCHANGED BY AIR FLOW T1 (t) conduction Ts (t) = T1 RADIATED  THROUGH  OPENINGS ABSORBED  BY WALLS Luisa Giuliani     ‐ Ts (x, t) radiation Fire safety design of steel structures To
  • 49. Problems Approach and methodology Motivation Heating curve of uninsulated steel heat ceased in a time interval  [J] increment of internal energy [J] ΔQ            ΔU   α  Fs  (T g  ‐ Ts )   Δt           ρ s  c p,s  V s    ΔT s    Tg (t) Tg ‐ Ts Fs α ΔT s            (T g  ‐ Ts )   Δt    ρ s  c p,s V s convection Ts = Ts (Ts) radiation  NUMERICAL  SOLUTION =  (Ts) cp,s = cp,s (Ts) Luisa Giuliani     ‐ Fire safety design of steel structures Ts (t) Ts (t) To
  • 50. Insulated steel Motivation INTUMESCENT PAINT after fire Problems Approach and methodology before fire Ponticelli&Caciolai, 2008 Luisa Giuliani     ‐ Fire safety design of steel structures
  • 51. Problems Approach and methodology Motivation Insulated steel Thermal resistance of the insulation VARIES WITH THE TEMPERATURE!! TR = din /  in insulation  thickness [m] [m2 K / W] insulation conductivity  [W/(m K)] din(t) CONDUCTIVITY VARIES WITH TEMPERATURE… din  = thin in in (Tin (x, t))                               in in (Tin (t)) conduction Tg (t) THICKNESS OF INTUMESCENT PAINT VARIES TOO… Tin (t) high expansion intumescent before and after furnace heating Ts (t) Ts (t) Luisa Giuliani     ‐ To Fire safety design of steel structures MSc PROJECT AT DTU!
  • 52. Motivation Structural fire design: main steps Fire design process Ponticelli&Caciolai, 2008 FIRE ACTION 1 Problems FIRE COURSE 2 3 1 RESISTANCE STIFFNESS Approach and methodology 2 1 modeling of fire action Luisa Giuliani     ‐ 3 material properties Fire safety design of steel structures ELEMENT  TEMPERATURE 3 MATERIAL  DEGRADATION
  • 53. Problems Approach and methodology Motivation Steel mechanical properties degradation STIFFNESS, ELASTIC LIMIT, RESISTANCE  sw B52  EC 1‐2 <=100°C fyk 200°C 400°C 500°C 600°C 800°C T 0.2% Luisa Giuliani     ‐ 2% Fire safety design of steel structures  15% 20%
  • 54. Approach and methodology Motivation 3a. Material behavior: steel degradation Degradation of stiffness and resistance 2% stress considered for yielding  20°C fy f yT 500°C fpT E Problems ET  p Luisa Giuliani     ‐ 2% Fire safety design of steel structures 15% 20%
  • 55. Approach and methodology Motivation 3b. Material behavior: steel degradation Degradation of stiffness and resistance 0.2% proof stress considered for yielding  20°C fy f0.2T 500°C fpT E Problems ET  0.2 % Luisa Giuliani     ‐ p Fire safety design of steel structures 15% 20%
  • 56. Approach and methodology Motivation 3. Material behavior: steel degradation 2) SWEDISH METHOD NATIONAL DANISH ANNEX 1) EUROCODES 2.0% effective yield stress 1,2 1,2 1 1 Stiffness Resistance 0,8 0,8 0,6 0,6 Resistance Stiffness 0,4 Problems 0.2% proof stress RESISTANCE 0,4 0,2 0,2 0 0 0 200 Luisa Giuliani     ‐ 400 600 800 1000 1200 0 Fire safety design of steel structures 100 200 300 400 500 600
  • 57. Approach and methodology Motivation 3c. Material behavior: steel degradation Degradation of stiffness and resistance Elastic‐perfectly plastic with hardening 20°C fy fuT 500°C fpT E Problems ET  p Luisa Giuliani     ‐ Fire safety design of steel structures u 20%
  • 58. Motivation Structural fire design: main steps Fire design process Ponticelli&Caciolai, 2008 FIRE ACTION 1 Problems Approach and methodology 2 FIRE COURSE 2 3 RESISTANCE STIFFNESS 1 1 modeling of fire action 2 heat transmission     Luisa Giuliani     ‐ 3 4 ELEMENT  TEMPERATURE 3 MATERIAL  DEGRADATION material properties structural behaviour Fire safety design of steel structures 4 VERIFICATION OR DESIGN
  • 59. Problems Approach and methodology Motivation 4. Verification: material safety coefficients a. RESISTANCE CLASSES b. FULLY DEVELOPED c. PBFD most probable yielding  resistance 5% fractile 5% fractile of 2.0% effective yield stress of 0.2% proof stress charact. value charact. value medium value fyd = fyk / γm fyd = fyk / γm fyd = fym / γm γm = 1.0 γm = 1.0 γm = 1.0 Luisa Giuliani     ‐ Fire safety design of steel structures + hardening!
  • 60. Problems Approach and methodology Motivation 4. Verification: load safety coefficients 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 1.00 1.30 0.50 1.00 1.00 EN: conservative ULS loads 0.50 DANISH STANDARD EXAMPLE OF DS: conservative ALS loads FLOOR LOAD Ultimate Limits state  (ULS) Accidental Limit State  (ALS) ALS/ULS EUROCODE 8.49 kN/m2 4.55 kN/m2 0.54 7.15 kN/m2 6.25 kN/m2 0.87 DANISH STANDARD Luisa Giuliani     ‐ Fire safety design of steel structures
  • 61. Problems LEVEL OF VERIFICATION SLS severity FIBER SECTION ELEMENT STRUCTURE Luisa Giuliani     ‐ y (+ deform. check) complexity Approach and methodology Motivation 4. Verification: collapse criterion Mu ULS ALS (Eurocodes) ALS (Swedish method) PBFD  (displacement limits) Fire safety design of steel structures Pu max < L2 / 800 H max < L/20
  • 62. Fire safety design of steel structures FIRE SAFETY DESIGN OF STEEL STRUCTURES 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 Assistant Professor, Ph.D., P.E. lugi@byg.dtu.dk DTU ‐ BYG Civil Engineering Department Technical University of Denmark
  • 63. Motivation Structural analysis issues A THERMAL  EFFECTS THERMAL  EXPANSION Problems Approach and methodology INDIRECT STRESSES B LARGE  DISPLACEMETS C COLLAPSE  CRITERION Luisa Giuliani     ‐ Fire safety design of steel structures
  • 64.  therm = (T) ∙ T [ad.] relative thermal elongation (L/L0 ) =  ∙ T Problems Approach and methodology Motivation A. Thermal expansion Luisa Giuliani     ‐ Fire safety design of steel structures [ad.]
  • 65. Total deformation:   tot = therm(T) + mech(,T) not hindered partially hindered relative thermal elongation Ltherm/L = (T) ∙ T [ad.] thermal expansion coefficient [K‐1] elongation + induced deformation Luisa Giuliani     ‐ hindered eigenstresses RESTRAIN  GRADE elongation and compression + induced deformation and stresses Problems Approach and methodology Motivation A. Thermal expansion Fire safety design of steel structures eigen(T, ET)  Ltherm(T)  eigen = kET E20 Lfree /L compression + induced stresses
  • 66. Total deformation:   tot = therm(T) + mech(,T) not hindered partially hindered relative thermal elongation Ltherm/L = (T) ∙ T [ad.] thermal expansion coefficient [K‐1] elongation + induced deformation RESTRAIN GRADE Lreal = ∙ lfree eigen = kET E20 (1 ‐  ∙ Lfree /L elongation and compression + induced deformation and stresses Problems Approach and methodology Motivation A. Thermal expansion Luisa Giuliani     ‐ Fire safety design of steel structures hindered eigenstresses eigen(T, ET)  Ltherm(T)  eigen = kET E20 Lfree /L compression + induced stresses
  • 67. Problems Approach and methodology Motivation A. Indirect stresses restrain  coefficient ΔL realized  realized    hindered  ΔL ΔL realized ΔL γ ΔL free displacement of the beam ΔL realized  LB,real ΔN K B, flex displacement of the column ΔL hindered    T ΔN K C,ax T N N + N LC hind 1  γ  1 LC KB,flex T T K C,ax T T K C,ax  K B,flex    1 totally free a b LB Luisa Giuliani     ‐ T T K B,flex  K C,ax    0 totally hidered Fire safety design of steel structures
  • 68. Motivation A. Indirect stresses  hinged at both ends clumped at both ends 1,0 E B  IB L B 3 K E C  A C /L C Approach and methodology 0,9 0,8 0,7 0,6  γ  0,5 1 1  48 K 0,4 0,3 Problems 0,2  γ  0,1 1 1  192  K K 0,0 0 0,01 Luisa Giuliani     ‐ 0,02 0,03 0,04 0,05 0,06 Fire safety design of steel structures 0,07 0,08 0,09 0,1
  • 69. design of column Load bearing capacity of restrained columns is much lower!! Problems Approach and methodology Motivation A. Indirect stresses Luisa Giuliani     ‐ Fire safety design of steel structures
  • 70. A. Indirect stresses Problems Approach and methodology Motivation indirect stresses sw B52 EC 1‐2 CONSIDERED DISREGARDED for buckling verification in case standard fire is used ΔLfree Δσ eigen  E 1 ‐   L ISO834  ∆σ eigen  0 T free  ΔL  N 1 1   T   T  20 AE E  T   L  severe fire 1  γ  1 KB,flex T K C,ax T t verification on single columns, but effect of adjacent element is considered Luisa Giuliani     ‐ verification on single members  without effect of adjacent element Fire safety design of steel structures
  • 71. Problems Approach and methodology Motivation Structural analysis issues A THERMAL  EFFECTS THERMAL  EXPANSION INDIRECT STRESSES BOWING EFFECT B LARGE  DISPLACEMETS CATENARY/MEMBR.  ACTION C COLLAPSE  CONDITION Luisa Giuliani     ‐ Fire safety design of steel structures higher displacements induced possible overloading of elements
  • 72. Approach and methodology Motivation B. Large displacements Q 1. A vertically loaded simply supported beam is exposed to fire. The sliding support: a. will stay still b. 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? simply supported horizontally restrained L L Problems WHEN DISPLACEMENT ARE LARGE THESE BEAMS BEHAVE DIFFERENTLY UNDER VERTICAL LOADS Luisa Giuliani     ‐ Fire safety design of steel structures
  • 73. Problems Approach and methodology Motivation B. Large displacements Q 1. A vertically loaded simply supported beam is exposed to fire. The sliding support: a. will stay still b. 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? simply supported horizontally restrained N N L L  first expansion then contraction first compression then tension A Luisa Giuliani     ‐ Fire safety design of steel structures
  • 74. simply supported beam horizontally restrained beam q q T T 1 2 thermal effect prevails  expansion compression  II ord. moment LD prevails  bowing effect Problems Approach and methodology Motivation B. Large displacements Luisa Giuliani     ‐ Fire safety design of steel structures tension  catenary action
  • 75. Approach and methodology Motivation Structural analysis issues A THERMAL  EFFECTS THERMAL  EXPANSION INDIRECT STRESSES BOWING EFFECT B LOW RESTRAIN Problems possible overloading of elements possible loss of supports LARGE  DISPLACEMETS CATENARY/MEMBR.  ACTION C higher displacements induced COLLAPSE  MODE HIGH RESTRAIN Luisa Giuliani     ‐ Fire safety design of steel structures generally beneficial for members
  • 76. B. Collapse mode: sway collapse of industrial hall Denmark 2013 Romania 2010 Alexandru Dondera, MSc thesis, 2013  Luisa Giuliani     ‐ Fire safety design of steel structures
  • 77. B. Collapse mode: early beam buckling of tall buildings HIGH RESTRAINT  = 0.9 THERMAL BUCKLING 600 500 Axial Force (kN) LOW RESTRAINT 700 400 PLASTIC HINGE 300 200 100 0 ‐100 0 100 ‐200 200 300 400 500 600 Temperature (°C) 700 800 900 1.000 TENSILE COLLAPSE IPE 270 HE 1000 M Riccardo Aiuti, MSc thesis, 2013  Luisa Giuliani     ‐ Fire safety design of steel structures
  • 78. Problems Approach and methodology Motivation B. Collapse mode: vertical propagation WTC, Usmani&al.2003 Luisa Giuliani     ‐ Fire safety design of steel structures
  • 79. Approach and methodology Motivation Structural analysis issues A THERMAL  EFFECTS THERMAL  EXPANSION INDIRECT STRESSES BOWING EFFECT B LOW RESTRAIN Problems possible overloading of elements possible loss of supports LARGE  DISPLACEMETS CATENARY/MEMBR.  ACTION C higher displacements induced generally beneficial for members Sway collapse COLLAPSE  MODE HIGH RESTRAIN Luisa Giuliani     ‐ Fire safety design of steel structures Early buckling, possible PC
  • 80. Fire safety design of steel structures LEARNING OBJECTIVES 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 main difference in each of the 4 design steps for structural verification and design. IV. Problems: Explain how mutual stiffness of beams and columns and large displacements determines sway collapse and buckling collapse of steel structures. Luisa Giuliani Assistant Professor, Ph.D., P.E. lugi@byg.dtu.dk DTU ‐ BYG Civil Engineering Department Technical University of Denmark