1 / 72

Fire Safety Engineering & Structures in Fire

Fire Safety Engineering & Structures in Fire. Structural Fire Engineering – Introduction. Workshop at Indian Institute of Science 9-13 August, 2010 Bangalore India. Preliminaries. Martin Gillie Acknowledge Prof. Asif Usmani Many former and current Phd students

rflynn
Download Presentation

Fire Safety Engineering & Structures in Fire

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Fire Safety Engineering & Structures in Fire Structural Fire Engineering – Introduction Workshop at Indian Institute of Science 9-13 August, 2010 Bangalore India

  2. Preliminaries • Martin Gillie • Acknowledge • Prof. Asif Usmani • Many former and current Phd students • The fire group at Edinburgh • Other fire researchers • Aims • Introduce research background • Describe key aspects of analysis and design of heated structures • Presentations • Introduction • Material behaviour at high temperature • Heat transfer in structures • Structural mechanics at high temperature • Modelling of heated structures • Comments on design codes

  3. Fire is a “load” on structures Caracas Los Angeles Taipei

  4. Piper Alpha Mont Blanc Kings Cross Kobe

  5. INTRODUCTION • Traditional fire design is geared towards FIRE PROTECTING steel so that temperatures remain below 550°C (in a standard fire test) • Two well-recognised problems with this approach • Fire scenario is artificial • Whole structure response is very different from single element response • 500C is still a high temperature – no guarantee of conservatism

  6. Traditional fire resistance design of steel structures • Standard fire resistance test • Standard fire • Single elements of construction • axially unrestrained • Applied fire protection to reduce the temperature of steel during a fire

  7. The fire resistance test • History • Procedure formalised ~80 years ago (based on test done ~100 yrs ago) • Standard temperature-time curve -1918(USA), 1932(UK) • Testing single elements or assemblies • Unrestrained (UK) • Restrained/unrestrained (USA) • Furnace • Characteristics differ around the world • No two furnaces provide the same exposure

  8. Column tests

  9. Test criteria • Stability • the ability of a load bearing element of construction to continue to perform its function • Integrity • prevent passage of flames or gases through holes, cracks, fissures or by collapse (cotton pad) • Insulation • should not allow the temperature rise on the unheated side of the element to exceed 140°C above its initial value

  10. Standard fire curves No cooling branch Logarithmic curve T=To+345(log0.113t+1)

  11. Standard and Natural fires

  12. Standard fire test in furnace • Determinate: so stresses governed by equilibrium and depend on applied load • Free expansion of heated beam • Deflections dominated by mechanical strains at given stress level • “Runaway” collapse when strength declines to stress value corresponding to loading

  13. Failure of a simple beam

  14. Need for new methods • Despite the obvious lack of scientific rigour traditional design approach has provided good service, so why change? • The economic burdens of fire in general • Order of 1% of GDP in industrialised countries • Overall total economic burden of fire in USA over $128 billion! Not including losses of productivity, environmental impact • Innovative designs not possible or difficult using the Standard Fire test approach • Need for ability to understand and predict real structural behaviour.

  15. Cost of Fire • Fire costs as % of GDP (Snell, 2001) • USA 0.80 • Japan 0.78 • UK 0.66 • Canada 0.91 • Design methods based on poor science are inefficient • increased burden on economy • less competitive! • Very inflexible – innovative design difficult.. • Solution: Applying better science & technology=>RESEARCH

  16. Research Context • Natural fire vs. standard fire has attracted considerable effort • Heat transfer models are reasonably reliable for design • Steel material behaviour to heating reasonably well know • Concrete behaviour less predictable • Relatively less effort on understanding whole structure response, until recently

  17. UK situation in Composite Steel-Concrete design c1997 • Nearly all design geared towards maintaining steel temperatures below 550°C through fire protection • UK fire protections costs are approximately 15% of total structural steel cost, reduced from over 20% in 1981, but not through any changes in design procedures

  18. Milestone events in UK • A number of severe accidental fires • Broadgate Phase 8 (1990,London,under-construction & unprotected) • Fire temperatures of over 1000 °C, no structural failure • Structural repairs 5% of total repair cost • Churchill Plaza (1991,Basingstoke,built 1988,protected for 90-min) • Fire engulfed -floors (8-10 of 12 storeys), complete burnout in 4 hrs • Total repair cost £17m. No structural damage or repairs

  19. Milestone experiments • Evidence suggesting that the prevalent fire design procedures were grossly over-conservative was getting stronger • Six full scale fire tests were performed at the BRE large building test facility at Cardington (4 by British Steel - Now Corus & 2 by BRE) in 1995-96 • Variety of fire compartments with mostly unprotected beams and protected columns • Again no structural collapse occurred

  20. BRE Large Building Test Facility

  21. Cardington Frame

  22. 3x5 bay frame: 4 tests by British Steel

  23. 2 tests by BRE

  24. Restrained beam test

  25. Restrained beam test

  26. Restrained beam test • 3mx8m compartment testing 305x165 mm unprotected secondary beam spanning 9m between 254x254 mm columns. • Maximum deflection (midspan) 232 mm at 887°C • Beam lower flange buckles at both ends just inside the compartment with tensile cracking in concrete slab • The best test to benchmark computational codes and other analytical models (because its simple and most key events occur)

  27. BS TEST2: “Plane Frame”

  28. Plane frame test

  29. Plane frame test • 3mx21m compartment (whole building width) with all beams unprotected and columns unprotected over the top 800mm • Columns squash at 670°C steel temperature (max. atmosphere temperature was 750°C) • Primary beam to secondary beam connections failed due excessive deflection of primary beam and the squash event • Main lesson “always protect columns to full exposed height”

  30. BS TEST 3: “Corner Test”

  31. Corner Test: Plan

  32. Corner test

  33. Corner test • 10mx7.5m compartment with atmosphere temperatures over 1000°C. All internal beams unprotected (edge beams protected) • Maximum deflection 428 mm at steel temperature of 935°C at midspan of the middle secondary beam, with deflection recovering to 296 mm after cooling • The lower flanges of all unprotected beams buckled • The best test to benchmark computational codes and other analytical models for 3D behaviour

  34. BS TEST4: “Demonstration Test”

  35. Demonstration Test: Plan

  36. Demonstration Test

  37. Demonstration test

  38. Demonstration test • Large compartment simulating and open plan office • Real office equipment and wood cribs equivalent to 46 kg/m2 fire load density. • All steel beams unprotected • Maximum deflections of 650 mm achieved with unprotected steel reaching 1150°C. Concrete temperatures were not recorded • Considering the high temperatures achieved and no steel protection this test (along with BRE large compartment test) provides the greatest confidence in robustness of behaviour • Difficult test to model as no concrete temperatures available

  39. Milestone modelling event • Edinburgh University (with British Steel and Imperial College) began the project for computational modelling of the Cardington fire tests (Sept 1996 to March 2000) with DETR funding • Objective: • ‘To understand and exploit the results of the large scale fire tests • at Cardington so that rational design guidance can be developed • for composite steel frameworks at the fire limit state’

  40. British Steel Test 1 (Restrained beam test)

  41. Grillage model for Restrained beam test

  42. Deflected model

  43. Deflections

  44. Total axial force in the composite beam

More Related