Structures in Fire Yesterday, Today and Tomorrow

1. 8th IAFSS Symposium Beijing, 18-23/9/2005 Structures in Fire Yesterday, Today and Tomorrow Jean-Marc Franssen jm.franssen@ulg.ac.be http://www.structuresinfire.com Mécanique des matériaux & Structures

2. Part 2: Dynamic analyses • I • II • III Plan of this presentation • Part 1: General considerations • A • A.1 • A.2 • B • B.1 • B.2 • C • C.1 • C.2 • D • D.1 • D.2 • D.3 • D.4 ……….Dynamic analyses

3. Part 1 of the presentation: General considerations Various methods for determining the fire resistance. • Experimental Tests • Tabulated data • Simple calculation models • Advanced calculation models

4. Test setup at NIST • Method 1 : Experimental testing • Testing specimens for material behaviour

5. Method 1 : Experimental testing • Testing material behaviour • Standard fire tests. • Circumstancial disadvantages: cost, delays, limited # of facilities. • Real disadvantages: only elements, size of the element, • boundary conditions, variability.

6. Picture from Nakamura et al., 1rst IAFSS, Gaithersburg, 1985 • Method 1 : Experimental testing • Testing material behaviour • Standard fire tests • Small scale fire tests • Steel: OK • Hydral materials: ???

7. Courtesy: T. Lennon - B.R.E. • Method 1 : Experimental testing • Testing material behaviour • Standard fire tests • Small scale fire tests • Large scale fire tests • Rare - Local fires - Observations more than research

8. Experimental testing is used mainly in research. • Experimental testing will remain for ever. • Verification of basic hypotheses used in calculation models • Integrity criteria in separating elements

9. Method 2 : Tabulated data Definition: presentation, in simple form, of results obtained by other methods.

10. Method 2 : Tabulated data • Available for simple members submitted to the standard fire. • Used mainly for masonry, concrete and composite elements, • not so much for steel. • Quite valuable for a preliminary design. • Interpolation software, please. • Background: ???

12. Method 3 : Simple calculation models Definition: Method based on global equilibrium conditions.

13. Method 3 : Simple calculation models • Extrapolations of similar methods used at room temperature • Can be used by hand • One method for each material/member type. • Not well suited for complex structures. • => Used for real projects.

14. Method 4 : Advanced calculation models Definition: Based on principles of structural mechanics or of heat transfer (local equations).

15. Method 4 : Advanced calculation models • Finite differences, finite elements, boundary elements. • Require a computer (numerical calculation models).

16. Method 4 : Advanced calculation models Three different families of software: • 'My Ph.D.' software • One author (university)

17. Method 4 : Advanced calculation models Three different families of software: • 'My Ph.D.' software • One author (university) • Limited field of application

18. Method 4 : Advanced calculation models Three different families of software: • 'My Ph.D.' software • One author (university) • Limited field of application • Limited availability This is MY software !!!

19. This is MY software !!! Method 4 : Advanced calculation models Three different families of software: • 'My Ph.D.' software • One author (university) • Limited field of application • Limited availability • Limited durability

20. Method 4 : Advanced calculation models Three different families of software: • 'My Ph.D.' software • Dedicated software (VULCAN, SAFIR,…) • From a group (University)

21. Method 4 : Advanced calculation models Three different families of software: • 'My Ph.D.' software • Dedicated software (VULCAN, SAFIR,…) • From a group (University) • Wider field of application

22. Method 4 : Advanced calculation models Three different families of software: • 'My Ph.D.' software • Dedicated software (VULCAN, SAFIR,…) • From a group (University) • Wider field of application • Become available now $ $ $ $ $

23. Method 4 : Advanced calculation models Three different families of software: • 'My Ph.D.' software • Dedicated software (VULCAN, SAFIR,…) • Commercial software (ANSYS, ABAQUS,…) • Widely distributed, used and validated • Price !!! • Nice graphics ? + + + or - - -

24. Method 4 : Advanced calculation models Yesterday Today Uniform temperature Non uniform temperature Linear gradient

25. Method 4 : Advanced calculation models Yesterday Today Single members or 2D frames 3D analyses

26. Method 4 : Advanced calculation models Yesterday Today Linear elements Shell elements

27. Method 4 : Advanced calculation models Yesterday Today Several types of F.E. One type of F.E.

28. Method 4 : Advanced calculation models Yesterday Today Dynamic analyses Static analyses See part 2 of this presentation

29. Method 4 : Advanced calculation models Tomorrow • Very large models • Connections • C.F.D. - F.E. interconnection • Spalling of concrete • Cooling phase of the fire • Moisture movements (e.g. in wood) • Shear strength of concrete • Mechanical properties of gypsum • …

30. Part 2 of the presentation: Dynamic analyses

31. Successive static analyses used to load a structure at room temperature

32. Successive static analyses used to take into account the temperature increase

33. Normal evolution toward failure

34. Local or temporary failure at T3

35. Local or temporary failure caused by: • geometrical reasons (buckling of one bar in a statically indeterminate sytem), • material behaviour (descending branches in s-e relationships).

36. Various solutions sometimes used: • Remove the unstable element from the structure. • Use « modified » s-e relationships. • Use non-tangent stiffness matrix. • Use « Riks » type methods (arc-length).

37. NEWMARK method with and Solution implemented in SAFIR: DYNAMIC ANALYSIS

38. Case study 1 : 1D axial oscillator 20°C, elastic

39. No damping

40. Damping = 1.5%

41. Damping = 50%

42. Case study 2 : 2D snap through 20°C, damping = 1.5%

43. Elastic

44. Elasto-plastic

45. Case study 3 : EC3 steel, heated bracing in a sway frame

46. u Evolution of the horizontal displacement

47. Evolution of the axial force in the diagonal N

48. Case study 4 : EC3 steel, 1 out of 2 bays heated

49. t = 25’

50. t = 26’30’’