欧洲建筑防火规范（Introduction to Eurocode Structural Fire Engineering）

1、1 2 strain (%) 0.51.01.52.0 stress (n/mm2) 0 300 250 200 150 100 50 20c 200c 300c 400c 500c 600c 700c 800c lsteel softens progressively from 100-200c up. lonly 23% of ambient- temperature strength remains at 700c. lat 800c strength reduced to 11% and at 900c to 6%. lmelts at about 1500c. 3 1.0 0.9 0

2、.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 1234 1000c 800c 20c 200c 400c 600c strain (%) normalised stress lconcrete also loses strength and stiffness from 100c upwards. ldoes not regain strength on cooling. lhigh temperature properties depend mainly on aggregate type used. 4 reaction occurs when oxygen/fuel

3、mixture hot enough 5 cooling . iso834 standard fire curve ignition - smouldering pre-flashover heating post-flashover 1000-1200c natural fire curve time temperature flashover 6 300 100 200 0 400 500 600 700 800 900 1000 060012001800240030003600 time (sec) gas temperature (c) 576 675 739 781 842 945

4、utesminint)1t 8log(34520 7 200 400 600 800 1000 1200 0120024003600 time (sec) gas temperature (c) typical ec1 parametric fire curve external fire standard fire hydrocarbon fire lfire resistance times based on standard furnace tests - not on survival in real fires. lec1 parametric fire temperature-ti

5、me curves. based on fire load and compartment properties (500m2). only allowed with calculation models. 8 compartment temperature load-bearing resistance time time fire severity time equivalent lused to rate fire severity or element performance relative to furnace test. lmatches times to given tempe

6、rature in a natural fire and in standard fire. fire resistance time equivalent standard fire natural fire element 9 fire testing lload kept constant, fire temperature increased using standard fire curve. lmaximum deflection criterion for fire resistance of beams. lload capacity criterion for fire re

7、sistance of columns. problems llimited range of spans feasible, simply supported beams only. leffects of continuity ignored. beams fail by “run-away”. lrestraint to thermal expansion by surrounding structure ignored. 10 100 200 300 0120024003600 time (sec) deflection (mm) 11 100 200 300 012002400360

8、0 time (sec) deflection (mm) span2/400d if rate tfi.requ load resistance:rfi.d.t efi.d.t temperature: cr.d d usually only directly feasible using advanced calculation models. feasible by hand calculation. find reduced resistance at design temperature. most usual simple ec3 method. find critical temp

9、erature for loading, compare with design temperature. 19 steel l mechanical (effective yield strength, elastic modulus, . ) concrete l thermal (thermal expansion, thermal conductivity, specific heat) l mechanical (compressive strength, secant modulus, . ) l thermal (thermal expansion, thermal conduc

10、tivity, specific heat) 20 lstrength/stiffness reduction factors for elastic modulus and yield strength (2% strain). strain (%) 0.51.01.52.0 stress (n/mm2) 0 300 250 200 150 100 50 20c 200c 300c 400c 500c 600c 700c 800c lelastic modulus at 600c reduced by about 70%. lyield strength at 600c reduced by

11、 over 50%. 21 rft 03006009001200 100 80 60 40 20 % of normal value temperature (c) rft effective yield strength (at 2% strain) ss elastic modulus ss strength and stiffness reductions very similar for s235, s275, s355 structural steels and hot-rolled reinforcing bars. (ss) cold-worked reinforcing bar

12、s s500 deteriorate more rapidly. (rft) 22 100 50 0 2004006008001000 1200 temperature (c) 6 5 4 3 2 1 strain (%) strength (% of normal) strain at maximum strength normal-weight concrete laccurate for normal density concrete with siliceous aggregates. lconservative for normal density concrete with cal

13、careous aggregates,. lightweight concrete lconservative for light- weight concretes. all types treated the same. strength reduction factors 23 stress-strain relationship in cooling from 700c (at 400c) stress-strain relationship in heating phase (700c) 5 15 25 0,010,020,03 stress-strain relationship

14、at ambient temperature stress-strain relationship in heating phase (400c) stress-strain relationship after cooling from 700c (at 20c) 24 0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 100 200 300 400 500 600 700 800 900 temperature (c) expansion coeff /c (x 10-6) steel steel thermal expansion stops during cr

15、ystal structrure change in the 700-800c range. normal-weight concrete concrete unlikely to reach 700c in time of a building fire. lightweight concrete light-weight concrete treated as having uniform thermal expansion coefficient. 25 la=45w/mk (ec3 simple calculation model) thermal conductivity (w/mk

16、) 10 20 30 40 50 60 0200 400 600 800 1000 1200 temperature (c) steel ca=600j/kgk (ec3 simple calculation model) specific heat (j/kgk) 5000 0200 400600 800 1000 1200 temperature (c) 4000 3000 2000 1000 steel 26 nc lc nc lc may assume constant value for nc: 1,60 w/m.k may assume constant value for nc:

17、 1000 j/kg.k cc* specific heat cc (j/kg.k) 400 800 1000 1200 2006001000 c thermal conductivity lc (w/m.k) 2006001000 c 1 2 3 27 thermal analysis: both ec3 part 1.2 and ec4 part 1.2 unprotected and protected steel beams lower and upper flanges considerably different temperatures proper calculation of

18、 temperatures! temperature 28 th v a c 1 d .net m aa t .a temperature increase in time step t: 4 m 4 rres 8 r .net 27327310 x67,5h heat flux hnet.d has 2 parts: radiation: mgcc ,net h convection: steel temperature steel fire temperature 29 perimeter c/s area exposed perimeter c/s area h b 2(b+h) c/s area 90%! 30 steel temperature steel protection fire temperature dp some heat stored in protection layer. v a d c c p p aa pp heat stored in protection layer relative to heat stored in ste