Tampere University of Technology Research Centre of Metal Structures, Frami, Kampusranta 9 C, FI Seinäjoki, Finland

Transcription

1 EFFECT OF ZINC COATING ON STEEL TEMPERARURES AT ELEVATED TEMPERATURES RESEARCH TEAM: Keijo Fränti, Hilkka Ronni,, Markku Heinisuo, PRESENTATION: Keijo Fränti Tampere University of Technology Research Centre of Metal Structures, Frami, Kampusranta 9 C, FI-632 Seinäjoki, Finland METNET, Aarhus 211 1

2 Welded termowires on steel. Thermocouple wire type K IEC Cone calorimeter and measuring equipment of steel temperature METNET, Aarhus 211 2

3 3 different heat fluxes 25, 5 and 75 kw/m2 Measuring of temperatures - both sides of the specimen - air 1 mm above the specimen - apr. 1m from the cone METNET, Aarhus 211 3

4 Speciments: 1x1x2 mm3, S235JRG2 steel s 39 tests Chem. element C Mn Si S P % Four different type of test speciments were used; one non-coated and three different zinc layers Specimen group Average zinc coating, μm ,3 3 17,9 METNET, Aarhus 211 4

5 Photoes: Czech Technical University in Praque Similar tests have been done for open and hollow section profiles Furnace tests By Czech Technical University in Praque METNET, Aarhus 211 5

6 Faculty of Built Environment, Department of Structural Engineering Test results: 25 kw/m kw/m Average temperature of uncoated s Average temperature of zinc coated s Variation is very small Total warming of zinc coated specimen is clearly lower compared to non coated METNET, Aarhus 211 6

7 Faculty of Built Environment, Department of Structural Engineering 75 kw/m kw/m Average temperature of uncoated s Average temperature of zinc coated s Variation is small The final temperature of zinc coated specimen reaches the temperature of uncoated specimen Clear time lag appears METNET, Aarhus 211 7

8 Faculty of Built Environment, Department of Structural Engineering But 5 kw/m 2???? Thickness of zinc couting 1 Specimen Thickness of zinc coating 2 Specimen Thickness of zinc coating 3 Specimen Heat flux 5kW/m 2, zinc coating 1 surface of surface of Thikness of zinc coating 2 Specimen Heat flux 5kW/m 2, zinc coating Thikness of zinc coating 1 Specimen Thickness of zinc caoting 3 Specimen Heat flux 5kW/m 2, zinc coating Thikness of zinc coating 1 Specimen Thikness of zinc coating 2 Specimen Thivkness of zinc coating 3 Specimen large variation in the results just for this heat flux, especially with respect to time the inflection points of the curves are at the same temperature, but the time lag changes largely Note that different zinc layers don t correlate in results any thermo dynamical study has not yet been done so, we do not know exactly what happens at the hot galvanized surface final temperatures are the same compared to non coated specimens METNET, Aarhus 211 8

9 Temperature of open section specimens Temperature of hollow section specimens Results of tests made in Czech Technical University are well in line Furnace tests METNET, Aarhus 211 9

10 Estimation of resistance of galvanized steel Heat transfer equations: U Q in Q in Q out 4 4 T T h T T A t ; Stefan-Bolzmann and Newton gas steel gas steel m Assume that steel members do not affect to each others and they are in same temperature Q out = for steel temperature during the time interval Δt U Q T in steel Q out Am / V c 4 4 V c Tsteel T gas Tsteel h T gas Tsteel 4 4 T T h T T t gas steel gas steel A m t METNET, Aarhus 211 1

11 Clear time lag appears, even with thin wall (A m /V=) zinc coating gives more time to resque humans and save property ~ 6 min => +45 % ~ 4 min => +45 % METNET, Aarhus

12 Conclutions Zinc coating provides clear time lag compared to uncoated First minutes are the most critical in fire Thermo dynamical basis is still open => more studies Aging of galvanizing, effect of different alloys, etc. are open => more studies However, zink coating may mean that in some cases no fire protection is needed, or slight over-design is enough to reach required resistance in fire => Economical and environmental savings. METNET, Aarhus

13 to be continued. METNET, Aarhus

14 Thank you for your time METNET, Aarhus