Structural Fire Safety State of the Art Future Directions. Andy Buchanan University of Canterbury, New Zealand

Transcription

1 Structural Fire Safety State of the Art Future Directions Andy Buchanan University of Canterbury, New Zealand

2 Where have we come from? 1666 Great Fire of London 1900s - Prescriptive codes Fire Resistance Ratings Simple test methods No science Last 20 years - lots of change

3 What are the changes? INPUTS: Fire science Structural analysis Performancebased codes Structural Fire Safety OUTPUTS: Predictable behaviour Better science Safer buildings for less cost

4 What are our objectives? Who are the stakeholders? Building owner Designer Regulator Forensic investigator Researchers Manufacturers Code writers One building at a time Groups of buildings

5 How much time have we got? For one building: During an emergency Preliminary design Full design Risk assessment Forensic study minutes hours days months years

6 What are our objectives? Life safety vs property protection? Analysis Design Does better analysis give better design?

7 What are our objectives? Researcher Analysis Code writer One off designer Everyday designer

8 What do the regulators want? Prescriptive codes How to build it - don t ask any questions Anyone can do it limited education Performance-based codes Design accepted if performance is met Requires science and judgement

9 Performance based codes 1 New Zealand code structure 2 3 No calculations prescriptive Structural design Design from first principles

10 Performance based codes How well has it worked? Good for a start few players Big shift from property to life safety New entrants (cowboys with computers) National standards now being set Need to prescribe design fires

11 Analysis Fire science Thermal analysis Structural analysis Computing power

12 Predictive capacity Accuracy Computing power

13 Limits to predictive capacity INPUTS: Fire size Accuracy Location Geometry Restraint Materials Spalling Adhesion Assumptions COMPUTING: Micro-macro dilemma Troubleshooting Computing power OUTPUTS: Data overload What is failure? Knowledge of operator (education)

14 Micro-macro dilemma OK Whole structure Low resolution Critical regions Difficult Detail vs complexity OK High resolution NIST had this problem with WTC

15 Predictive capacity Computing power is out-stripping the ability to do improved analysis, because of: Limitations on input data Limited ability to handle output Lack of large scale test results Keep it simple.

16 What can we do now? Work on problems that can be solved Computer friendliness Data management Material properties More test data Thermal analysis Structural analysis.

17 What can we do now? What about the difficult problems? Fire size? Fire location? Sprinkler reliability? Changes in use? Fire after earthquake? Terrorist attacks? RISK ASSESSMENT

18 Risk Assessment Seismic engineering: 1. Determine statistical range of earthquakes 2. Subject the building to small, medium, large earthquakes 3. Calculate a distribution of effects 4. Estimate likely life-time cost of damage 5. Change the design, do it again 6. Quantify likely performance

19 Must use real fires with decay phase Risk Assessment Seismic Fire engineering: 1. Determine statistical range of earthquakes 2. Subject the building to small, medium, large earthquakes fires fires 3. Calculate a distribution of effects 4. Estimate likely life-time cost of damage 5. Change the design, do it again 6. Quantify likely performance

20 What are the differences? Earthquakes: Whole city affected Seismologists can estimate distribution Well established design procedures Fires: When do they happen? How severe are they? Do the sprinklers work? Better design methods needed

21 Case studies Cardington tests Concrete slabs and steel beams Concrete walls and steel portal frames Timber buildings What can we learn?

22 Cardington tests Good behaviour of unprotected steel frames Damage to property on the floor above?

23 Concrete slabs

24 Fire tests

25 SAFIR: In-plane forces Good analysis, with simple boundary conditions Red = Compression Blue = Tension

26 Realistic fires - decay phase temperatures ISO 834 fire ISO834 Standard fire with decay phase Temperature ( o C) Steel temperatures Top reinforcing bars Decay phase Bottom reinforcing bars Time (minutes)

27 Decay temperatures C1 B1 A1 Tensile forces increase as the fire goes out

28 Axial force development Time Temperature Deflection Time C Strength Time Time Axial force T

29 With decay phase Time Temperature Deflection Time C Strength Time Time Axial force T Tensile forces increase as the fire goes out

30 Hollow-core slabs Temperature in the voids Prestressing; no reinforcement Effects from surrounding structural members

31 Analytical model in SAFIR shell elements long. beam elements trans. beam el

32 SAFIR analysis Thermal analysis

33 Effect of seating details Correct boundary conditions are critical for predicting fire behaviour

34 Boundary conditions Pin roller Pin pin Fixed slide Fixed fixed

35 Steel portal frame

36 Fire behaviour Difficult to estimate fire severity

37 SAFIR model Complex problem: Difficult to give advice to designers Time = minutes

38 Modular precast concrete Why not do this in wood? Need to investigate fire performance

39 Multi-storey timber buildings

40 Prestressed timber What is the fire performance of members, and connections?

41 Wood properties in fire Cone calorimeter tests

42 Full-scale beam test Need thermal and mechanical properties of wood

43 Connection furnace

44 Bolted connection Need bearing strength of wood at elevated temps

45 Intumescent paint Difficult to calculate intumescent behaviour

46 Epoxied steel rods Difficult to calculate epoxy behaviour

47 Wood-concrete composite floors Need fire performance of wood, concrete and connections

48 Conclusions Structural fire engineering is challenging. Computer analysis is growing fast, but it is not enough on its own. We need knowledge about materials, structures, fires, computing, and testing. Design and analysis are different skill sets Risk assessment will add a new dimension Thank-you, questions please

49 Light timber factory wall Cannot calculate cracking of gypsum plaster

50 Timber structures Cone calorimeter - charring of LVL

51 Self-drilling dowels

52 Industrial buildings

53 What limits predictive capacity? Accuracy Our computing power is out-stripping our ability to do improved analysis Computing power

54 SAFIR analysis 0.00 Midspan vertical deflection (m) f t = 0 MPa f t = 1.5 MPa f t = 3.0 MPa Experimental results Time (Minutes)