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Evaluation of risk of breakage by thermal shock 2008

Evaluation of risk of breakage by thermal shock 2008. Technical Advisory Service. Thermal shock. Definition Parameters of influence Method of calculation Example of calculation. Thermal shock - Definition.

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Evaluation of risk of breakage by thermal shock 2008

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  1. Evaluation of risk of breakage by thermal shock 2008 Technical Advisory Service

  2. Thermal shock • Definition • Parameters of influence • Method of calculation • Example of calculation

  3. Thermal shock - Definition • A breaking by thermal shock occurs when there is a too high difference of temperature between two point of a annealed glass. • Indeed, if the temperature of the glass increases, this glass expands. • Reminder : Coefficient of linear expansion : 9.10-6 m/(m °C) Ex: T° difference of 50°C for a 2 m glass  9.10-6 m/(m °C) x 50°C x 2 m = 0,0009 m = 0,9 mm

  4. Thermal shock - Definition • This phenomenon does not present a problem if the increase in temperature is uniform on all the glazing and if the movement is not blocked. • On the other hand, if the border of the glazing remains cold, it will prevent the hot part from dilating freely and it results the beginning traction constraints. • At a certain difference of temperature between two points of a same glazing, there is a risk of thermal breakage.

  5. Thermal shock

  6. Thermal shock

  7. Thermal shock

  8. Thermal shock • Thermal breakage starts allways at the edge of the glass, perpendicular to the edge and the 2 faces. • The breakage can be single or multiple.

  9. Thermal shock

  10. Thermal shock • Definition • Parameters of influence • Method of calculation • Example of calculation

  11. Thermal shock – Parameters of influence • Climatic conditions • Parameters depending of the glazing and its setting • Outside « architectural » parameters • Inside « architectural » parameters

  12. Thermal shock – Parameters of influence • Climatic conditions : • Daily difference of temperature (°C) • Solar intensity (W/m²)

  13. Thermal shock – Parameters of influence • Parameters depending of the glazing and its setting • Nature of glass  Energy absorption (EA)

  14. Thermal shock – Parameters of influence • Parameters depending of the glazing and its setting • Type of setting and colour of the frame

  15. Thermal shock – Parameters of influence • Parameters depending of the glazing and its setting • Structural glazing • VGG • Alu with thermal break • Dark alu without thermal break • Middle alu without thermal break • Wood or PVC • Clear alu without thermal break • Dark steel • Clear steel • Concrete/Masonry

  16. Thermal shock – Parameters of influence • Parameters depending of the glazing and its setting • State of the glass edges : damaged edges or presenting chips increase the risk of thermal breaking, these one starting from these weak points.

  17. Thermal shock – Parameters of influence • Parameters depending of the glazing and its setting • Use of TV or sliding frame with Low E Toughened or heat strengthened glass

  18. Thermal shock – Parameters of influence

  19. Thermal shock – Parameters of influence • Parameters depending of the glazing and its setting • Glass in a roof Inside temperature Outside temperature

  20. Thermal shock – Parameters of influence • Outside « architectural » parameters • Exposure of the facade (in the Northern hemisphere)

  21. Thermal shock – Parameters of influence

  22. Thermal shock – Parameters of influence

  23. Thermal shock – Parameters of influence • Outside « architectural » parameters • Eventual shadows on the glazing (eaves of a building, blind) and letting only one part of the glazing in the shadow.

  24. Thermal shock – Parameters of influence

  25. Thermal shock – Parameters of influence

  26. Thermal shock – Parameters of influence

  27. Thermal shock – Parameters of influence

  28. more and more dangerous

  29. Thermal shock – Parameters of influence • Inside « architectural » parameters • Presence of blinds • Proximity of heating appliances • Proximity of the inside aeration forcing air system (hot or cold) on the glazing • Inside ceiling • Proximity of a dark object behind the glazing

  30. Thermal shock – Parameters of influence

  31. Thermal shock – Parameters of influence Minimum distance 20 cm Liquid temperature max 65°C

  32. Thermal shock – Parameters of influence h L Risk if L < h

  33. Thermal shock • Definition • Parameters of influence • Method of calculation • Example of calculation

  34. Thermal shock – « Glass in building » method 1°) Basic calculation of Dt : SV: Dt = I . AE + A . he he + hi he + hi With I = solar intensity (750 à 850 W/m²) A = maximum daily t° range (10 à 13 °C) DV: Dte = … Dti = …

  35. Thermal shock – « Glass in building » method 2°) Influence of the inside blinds : Dt1 = Dt + Dt’

  36. Thermal shock – « Glass in building » method 2°) Influence of the inside blinds : Values of Dt’

  37. Thermal shock – « Glass in building » method 2°) Influence of the inside blinds : Values of Dt’

  38. Thermal shock – « Glass in building » method 3°) Influence of the frame : Dt2 = Dt1 x f1

  39. Thermal shock – « Glass in building » method 3°) Influence of the frame :

  40. Thermal shock – « Glass in building » method 4°) Influence of the outside shadows : Dt3 = Dt2 x f2

  41. Thermal shock – « Glass in building » method 4°) Influence of the outside shadows

  42. Thermal shock – « Glass in building » method • Stress in the glass : • s = E . e = E . a . DT3 = 0,63 . DT3 • Criteria of acceptability : • DT3 < 30°C  OK • DT3 > 30°C  a thermal treatment (toughened or heat strengthened) is necessary

  43. Thermal shock – « Glass in building » method • Notes : • Thermal treatment can be toughened or heat strengthened glass • Advantage of a toughned glass : it is a safety glass against injuries too • Advantage or a heat strengthened glass : does not present a risk of spontaneous breakin and so, no heat soak treatment is needed

  44. Thermal shock – « Glass in building » method • Notes : • The edge treatment is not considered as a good solution to prevent of the risk of thermal shock • The spandrels must always be tempered

  45. Thermal shock • Definition • Parameters of influence • Method of calculation • Example of calculation

  46. Thermal shock – Example of calculation • Example of a calculation : • 6 mm Stopsol Supersilver Dark Blue pos.212 mm air6 mm Planibel clear • AEe = 55 • AEi = 4

  47. Thermal shock – Example of calculation • Example of a calculation : • 6 mm Stopsol supersilver Dark Blue pos.212 mm air6 mm Planibel clear • Setting in an aluminium frame with thermal break and outside shadow • DTe = 33,5 °C • DTi = 13,0 °C •  The glass outside must be tempered

  48. Thermal shock – Example of calculation • Example of a calculation : • 6 mm Stopsol supersilver Dark Blue pos.212 mm air6 mm Planibel clear • Setting in Structural glazing without shadow nor blind • DTe = 17,6 °C • DTi = 8,5 °C •  A thermal treatment is not necessary

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