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(1)International Congress FIRE COMPUTER MODELING UNIVERSIDAD DE CANTABRIA Dpto. de Transportes y Tecnología de Proyectos y Procesos GIDAI - Seguridad contra Incendios - Investigación y Tecnología Avda. Los Castros, s/n 39005 Santander. Espana

(2) International Congress FIRE COMPUTER MODELlNG Edited by: Jorge A. Capote Daniel Alvear Compiled by: Mariano Lázaro David Lázaro Virginia Alonso Acknowledgements: Servicio de Publicaciones (Universidad de Cantabria) FIRE COMPUTER MODELlNG : international congress, [Santander, 19 de Octubre de 2012J I edited by Jorge A. Capote, Daniel Alvear ; compiled by Mariano Lázaro , David Lázaro, Virginia Alonso-- Santander: Universidad de Cantabria, GIDAI, [2012J. D.L SA-608-2012 ISBN 978-84-86116-69-9 1.lncendios - Simulación por Ordenador - Congresos I. Capote Abreu, Jorge A, ed. li!. 11. Alvear Portilla, Daniel, ed. li!. 111. Lázaro Urrutia, Mariano 111. Universidad de Cantabria. Grupo de Investigación y Desarrollo de Actuaciones Industriales. 614.84 (063) Printed: Gráficas Iguna, S.A. ©COPYRIGHT. Ali rights reserved. Na part 01 this book may be reprinted or reproduced or utilized in any lorm ar by any electronic, mechanical, or other means, now know ar hereafter invented, inciuding photocopying or recording, or in any infonmation storage or retrieval system, without permission in writing Irom the editor.

(3) Hybrid wood/steel elements under tire Barbosa,L.F.M'; Almeida, P.M.L. '; Fonseca, E.M,M. 2; Barreira, L.M.S" ; Coelho, D.C,S,3 ! Mechanical Engineering, Polytechnic Institute of Bragança, 2 Department of Applied Mechanics, Polytechnic Institute of Bragança, !,2Campus de Sta , Apolónia, 5301-857, Bragança, Portugal, 3 Faculty of Engineering, Porto, ABSTRACT The main objective of this paper is to present a computational mo dei for the fire resistance of wood/steel hybrid elements , Different design solutions will be presented, The most important factors for fire safety in hybrid elements are the thermal effects degradation and the charring depth formation in wood materiais, and also the heat conduction extremely well in steel material. Unprotected steel elements under fire condition may suffer serious damage, The use of hybrid wood/steel elements could increase both structural strength and stiffness. Wood could be considered as an insulating material, the core section could remain at low temperature, function of fire exposure time and element cross section size. All presented results will permit to evaluate different design solutions, which facilitates the fire design of wood/steel hybrid elements, The presented study was conducted in arder to articulate the best constructive solution using the finite element method. 1 INTRODUCTION In the past, buildings have been entirely constructed with steel or entirely with wood, but recently have begun to integrate with both different materiais, using hybrid wood/steel solutions, [1-2]. Hybrid structure does not merely indicate a framework member composed by a combination of different materiaIs, but a construction using different methods according specific structural functions [2]. For this reason, the use of hybrid materiais could increase the structural integrity, Steel material has many advantages over wood elements, strength, stability, resistance to woodworm, among others. Steel is incombustible and most of the times it can full recover strength after fire. However, steel has one significant disadvantage over wood, steel material conducted heat extremely well, [3J, Wood is a renewable resource, recently attracted by public attention, as an environmentalIy friendly material. This product is a building material with attractive attributes, as architectural and structural aspects. The wood when exposed to accidental actions, such as fire conditions, has a surrounding charring depth. However, this layer can delay the heating process to the wood core section, acting as an insulating. By comparison with other traditional materiais applied to the building construction, wood exhibits an exceptional strength, contrarily to that occurs with steel elements, where the structural collapse may result from the deterioration of mechanical prope11ies with temperature increase, [4]. 407

(4) 408 INTERNATIONAL CONGRESS FIRE COMPUTER MODELL"IG The combination between wood and steel leads to economic and ecologic benefits, weight optimization, fire resistance increase, ealihquake resistance and an efficient assembJing [5]. Recently building codes and standards have been increasing the performance of structures in fue. Several researches have presented experimental and munerical mo deis for the study of wood degradation in presence of high temperatures [6-8]. The charring rate of softwood Of hardwood material exposed to fire conditions has been studied by researchers in different countries, [9-16]. Also, several studies have been presented to investigate the behaviour of steel elements under fire conditions, [17]. The greatest opportunity in fire research is the development of computational fire resistance models and experimental methodologies for hybrid materiais submitted to natural fire scenarios [18]. In this work the fust objective was to produce the temperature time history in different design solutions submitted to different fue scenarios. The second objective is to verifY the best constructive solution and compare the fue resistance. Ali mo deis were developed by the finite element method using ANSYS. 2 MATERIAL PROPERTIES The most important factors for structural strength in wooden elements submitted to fire are the material properties degradation and the charring deplh formation. The wood density decreases with the material degradation caused by the pyrolysis process, in the presence of high temperatures . For wood temperatures around 280[°C] to 300[°C] are general1y prescribed as the start of pyrolysis, [19]. Wood bums leading to material degradation and decomposition. The wood therrnal properties are strongly affected by temperature and moisture content levei . The thermal behaviour of wood is complex, but has been well documented. Eurocode 5 [20] provides lhe design values for wood thermal properties, for density, therrnal conductivity and specific heat, figure 1. The values below about 350[°C] represent the properties of wood and above 350°C represent the properties of charred layer. The specie (Spruce) considered in thi study presents a value of density equal to 450[kg/m3]. The thermal properties of steel are function of the temperature and should be determined from Eurocode 3 [21]. The density of steel is considered constant and equal to 7850[kg/m3]. The specific heat and the thermal conductivity of steel are represented in figure 2, [21]. Figure 3 gives the therrnal properties ofthe air with temperature dependence for specific heat, therrnal conductivity and density, [22]. The evolution offire temperature (Sa in [0C]) over time (t in [min]) was defined by standard fire curve. In this work the standard IS0834 fire curve was adopted, with the expression I, according the Eurocode 1 [23]: ()'" = 20 + 3451oglO (8t + 1) (1 )

(5) HYBRlD WOOD/STEEL ELEIvIENTS UNDER FIRE Barbosa,L.F.M; Almeida, P.ML.; Fonseca, E.MM; Barreira, L.MS.; Coelho, 14 ~ -, 409 D.c.s. -, - Specific heat [JlkgKJ - - Density ~- [ g! cm ~] Thennal conductiv; ty [W!mK) 2 ' 1 I .... _---500 250 1000 750 1250 Temperature [oq Fig. 1. Thermal properties ofwood. 60~ - - - - - -~ Specífic h~t(xlO)[J/kgK] -~ 50 --- TheJmal conductivity [WímK] 10 -----------~- 500 250 750 1000 1250 Temperature r"C] Fig. 2. Thermal properties of steel. 1.25 ~- - I'. ,, 1.00 0.75 -~ . , ...., ,, - ,, ..... , Specific h",t (,1000)[JlkgJ<) - - Density [glcm;) , --- Thennal conductivity [WimK) 0.50 0.25 0.00 -_ ..-- ----_ ..- --_ .. --- ---------_ .... ---_...- --_._--"'-_...-._- "'.... _.....- --,--_._-- -_ .. O 250 500 750 Temperature [0C] Fig. 3. Thermal properties of air. 1000 1250

(6) INTERNATIONAL CONGRESS 410 FlRE COMPUTER MODELJNG 3 STUDIED MODELS Table 1 represents three different geometries in study (Gl, G2 and G3), and the fire scenario, considering one side (lF) and three sides (3F). For each model, four different nodal positions were chosen to obtain the temperature evolution during one hour of fue exposure. Geometries Fire at three sides (3F) Fire at one side (1 F) ,i G1 - - - 'f I I I I I ~ ~ ~ G2 G3 Table I. Geometries and nodallocations. ~

(7) HYBRlD WOOD/STEEL ELEMENTS UNDER FIRE Barbosa,L.F. M ; Almeida, P.M L.; Fonseca, E.M M; Barreira, L.MS. ; Coelho, D.C.S. 41\ Table 2 represents a11 different combinations according to the material for each mode! (Wood, Steel, Wood-Steel). According to the fire scenario and the material combination, 24 different mo deis were considered in this study. Four of these models were considered with air in the internaI cavity. The air modelling permits to verify the heating conduction inside the void. Wood-Stee\ (WS) Steel-Wood (SW) G2-1F-W G2-3F-W G2-1 F-S G2-3F-S G2-1F-WS G2-3F-WS G2-1F-SW G2-3F-SW G3-1F-S G3-3F-S G3-1 F-S-air G3-3F-S-air G3-1F-WS G3-3F-WS G3-1 F-WS-air G3-3F-WS-air Table 2. 24 models andjire acliol1. The boundary conditions considered in a11 analysis are convection and radiation, according to the temperature evolution in fire . A transient thermal analysis was defined with ANSYS. A two dimensional finite element with eight nodes (PLANE77) was considered. AlI temperatures were obtained during one hour of fire exposure. Tables 3 to 8 represent the results for each mode! in ana!ysis, according to the time history for each chosen node and the temperature field distribution at 3600[s].

(8) INTERNA TIONAL CONGRESS 412 FIRE COMPUTER MODELING Time history, O to 3600[s] Temperatures at the end of 3600[s] 1000 - - " 900 _ _ _ _ _ _ _ _ _-::=.,.,.=-'=_'='_- ~- soo - "'. - . 2: ~- _ 7 '~ -- - 600 ~ ,$' - ~ ISO S ~ -- Node I ----- ' 400 - - ;::: 500 ,-- ,..-- - - - - . . . ~ -' ~ ----- · - -Nú " 100 •o --~ ... ' ; :~.400 .. 1100 1200 ~.'" : .r- .••-:.; ,; ,:;.~ 1600 :!00l .:-~ ••.-.-..::;:'.. 1400 2800 3100 G1-1F-S 1000 -ISO í! 34 900 '00 700 E 600 [ 500 ~ - - Nodc I ;:: 400 " 300 - · Nod,, 3 200 100 o o 400 ROO 1200 lól.:l 2000 2-\.00 2800 :UIll) 3600 --·Nooc4 G1-1F-WS 1000 -1501134 700 -- f'\o« I E..., •~ ! 500 . 400 : 300 ' 200 - ·1\",1..:3 lO<> o -.:= o -: 400 800 IZOO =- ~-= 1600 lDOO TinlCls! - ~ 2400 2XOO 3200 )tiOO ---'P\odo.:'" G1-1F-SW Table 3, Model G 1 and flre scenario (1 F).

(9) HYBRlD WOOD/STEEL ELEMENTS UNDER FIRE Barbosa,L.F.M; Almeida, P.ML , Fonseca, E.MM; Barreira, L.MS.; Coelho, Time history, O to 3600[s] 413 D.es. Temperatures at the end of 3600[s] 1000 - 900 ISQS3J ,ou -- N.:xkl 300 --Nooc) :(1) I~ ~' U o _ _ ' _ _ J" 400 SOO I:!OO "':;= ;:_ lóOO 1000 ': ':~=; 2400 ;:_~"= ' _ ' ~_ 21.100 3200 ' : _: 3600 "" N(MJc4 Timc(s) ~J:"! G1-3F-W i .~diI · bl.:J§1? - [SOI:l.M ' OI) ,~ )011 1) o 400 Il0l1 1200 1600 2110U ;woo 2Il00 l:!lD ) (,00 -· ~0lk:4 l'it't<' I ~ l G1-3F-S 1000 - lS0!CU 900 $OU -- Nod..: ! 400 1.100 1100 -1600 2000 2400 28()() .nou I 3600 --·- Nodc4 Timc [s] G1-3F-WS 1000 - 1$0834 HOtl 70() --Nudcl 2600 ~ E é' 500 • . -Nodc2 400 . 300 20(1 - ·Nm t ~.\ 11lO o L- 7 -"' o "'00 - -" 800 1:'00 16QO " ~= 2000 ;':-_ 24()() ' _2800 3200 3600 ·-·-:-.lode4 Timelli] G1-3F-SW Table 4. Model G 1 and fire scenario (3F). ·i:!>"'.~l-bJ;1 n . ~!.'Ji . ú'!,._"? '~i

(10) INTERNATIONAL CONGRESS 414 FlRE COMPUTER MODELING Time history, O to 3600[s] Temperatures at the end of 3600[s] 1000 - 900 '"" 7 ---- - 700 ~ G wo '- .\00 ! ' )00 __ L -- Node I , ~ -- - - ----.- ,,r 500 - ~ ~ I $O:U4 ~-' ; - -NOOc 3 100 O ~ - () -~ 400 ~ - SOO 1200 1600 " - - - 2000 - 2ROO 1400 3600 ----Nodc4 3~O Tim\"{.' ] G2-1 F-W lUOO - \lOO IS08 ~ -- ""rlI! I . ---- ~ = .. _.. 100 o _ O . :~ -=~ 4M ll M ~- 1200 It.OO - _ ._ - lOO') _ . _ 2400 . _ ~. ~O ~- _ ]200 · --1\0&: 2 .. 3600 - -·l\otlc4 Tintel sl G2-1F-S 1000 .00 - ISO 834 800 -- Nooe 1 300 200 100 O _ . Nodc3 ~: =":' O 400 .:=~ ~ : : :~ &00 ..........------_ ... -.. __ ..... =-. ~ =- ._ 1100 1600 2000 Ti n:c{s) 2-1 00 2800 3200 :1600 ---· Nm!,,--I G2-1F-WS 1000 - :50834 '00 E ~40 7W -- '.Jode! 600 !"- '00 3{)o · ··X00..:2 , • --N
(11) HYBRlD WOOD/STEEL ELEMENTS UNDER FIRE Barbosa,L.F.M.; Almeida, P.ML.; Fonseca, E.MM ; Barreira, L.M S.; Coelho, 41 5 D.es. Temperalures aI lhe end of 3600 [s] Time hislory, O lo 3600[s] -ISÚlI.l4 · · · N,Jdc2 - ·NoJc ) {' / ' . / 100 Ú '-- --- o -.----------- ------------- -.- ~o I:!OO .\(1<) 1600 2000 2400 21\00 .t:!oo j6(l(} ---·NOI.I<.:-I Timc[sJ G2-3F-W 1000 - I5OS):; 900 '00 70D -- No'.!" I 600 500 400 }OO '00 -100 1600 l!OO ~O 100() 2400 2800 3200 3600 --- -Nooc 4 Tim" fsl G2-3F-S - ISON3.1 -- Nodc l · · -J\'odc2 - 'NodcJ 400 800 1600 1200 !OOU 2400 2800 J:OO J600 -··· N«I,,-I Time[sj G2-3F-WS ,----j 1000 900 - ISO!l14 '00 , 7~) !Itl!':'j,.y·;ó;:,m: -- Nodc 1 i: 6(}O ~ 400 I i 500 · · - Nlldc2 JOO ;,' - ' NoJc ) 200 100 o~ ,';" o ...\00 ~O - - -l~ O , -. - .. - - - - - 1600 ~O 2400 2l!OO J200 3600 ---·Nüdc4 Tll1'c [s] G2-3F-SW h Table 6. Model G2 and fire scenario (3F). ,x.,~7s:·bil!_ ===-. Y.fiS4& . S<;."%5 . '>;"

(12) INTERl\ATIONAL CONGRESS FIRE COMPUTER MODELlNG 416 Time history, O to 3600[s] Temperatures ai lhe end of 3600[s] 1000 -ISO ":3.J 900 800 '00 -- Nodc3 100 -':"~,. :'~ .tOO ..:._---_ ..-~. !)()O 1200 -' 2000 16W - ~40 21<00 .l:!IX1 J600 ----Í'iOOt 4 Tltn.; [s ] G3-1F-S - 1000 "'lo - lSOK30() Tim ;:000 2400 2800 3200 3(;00 ----N(xk4 ;:r~J G3-1 F-S-air -1~ 900 OX~ ",Q 700 .... "'<'lI,: 1 E 600 ~ $00 J" 400 J 01l 200 ~_.:-; 100 " li : _: = : _____________. ____ _ ~;.: _: ~ ;~_ 400 800 1200 :~_ lóOO 2000 T imcLs] 2400 2800 3200 3600 ----:"\'OIj",4 G3-1F-WS 1000 'JOO ! ~ L. - IS O X.'4 700 : E r.oo ' ~m ~ -- Nudc I .. ... "'" "'" 100 • o~-",: - - No';,,) _ . _:",;'= .JOO ~ - -:. lIllfl 1200 :'_ 1600 : ~. _ •• __ ._--_._---------_.ZOOl} ! .. oo .v;un J:!OO J hnJ - ' -N
(13) HYBRlD WOOD/STEEL ELEMENTS UNDER FIRE Barbosa, L.F.M; Almeida, P.ML.; Fonseca, E.MM; Barreira, L.M S.; Coelho, D.C.S. Time history, O to 3600[s] li"" 417 Temperatures aI the end of 3600[5] 900 ·WO 1100 12()(J 1600 2000 24011 2S00 3200 .'600 ----.Nodc4 limeis] G3-3F-S - _ _:"Ii.~ 7):a.~3 1000 - 900 150 834 SOl) 700 ~ j ~O "- ~ -- NoJcl (>OI) · · -Nvdcl .100 ,jO(J - - '1odl:.1 400 SÔO 1200 1600 2000 rin..:[ s1 2400 2~O noo ----N
(14) INTERNA TTONAL CONGRESS F/RE COMPUTER MODELING 418 4 RESUL TS ANO OISCUSSION After ali simulations it is possible to identify different conclusions. The fire exposure at tlu'ee sides is the worst situation. For the same period of time, the temperature increases, in a11 elements. The interface between charred and noncharred wood is the demarcation plane between black and brown material and is characterized by a temperature of 300°C, according Emocode 5 [20]. Considering all different geometries and materiais: -For model G 1, the elements that have wood in front of the fire exposure, protects the core section. For materiais with steeI in front of the fire, the heat conduction is very high and quickly heats a11 components. -In the model G2, the wood elements in fIOnt of the fire are very thin, and quickly lose their resistance due the char layer formation, compromising the remaining structure. In this model the steel material has better performance. -For mo deI G3, when wood material is extemally applied to the steel profile, plays an important role as insulation, reducing the temperature inside steel. In the cases where both (outside and inside of the model) are made of steel, the temperature in the inner pro file is higher, than the previous solution. According to these results, it can be seen that wood elements present lower temperatures than steel, and the maximum temperature in the model is always inside the char layer. The hybrid modeI can perforrn well under fire conditions. Regarding the best design solution for a11 studied models, it is concluded that the hybrid model 3F-G3-WS has a good fire resistance even for three sides exposure, showing the ability of wood to protect the steel. REFERENCES 1. 2. U.S. Department of Housing and Urban Development, Stee1 Framing Alliance and NAHB Research Center Inc., Hybrid Wood and Steel Sole Plate Connection Wa11s to Floors Testing Report, American IIOn and Steel Institute / Steel Framing A11iance, 2003 , Revision 2006, Research Report RP03-4. Toshihiro, A., Marin, K., Naoyuki, 1., Masato, M., Kuniaki, I. T. O. , Design of a Hybrid Structure Consistillg of a Steel Beam String Structure and a Woodell HP Shell Reinforced by Aramid Fiber Sheets, Journal of the International Association for Shell and Spatial Structures IASS, 41 No. I34, 2000.

(15) HYBRID WOOD/STEEL ELEMENTS UNDER FJRE Barbosa,L.F. M ; Almeida, P.ML.; Fonseca, E.MM; Barreira, L.MS.; Coelho, D.es. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 419 Jan, K. , Phil, c., Making Steel Framing as Thermally Efficient as Wood Most Current Developments from ORNL, Proceedings of the Thirteenth Symposium on Improving Bui1ding Systems in Hot and Humid C1imates, Houston, TX, ESL-HH-02-05 -40, 20-22 May 2002. Fonseca, E. M. M., Barreira, L., Experimental and Numerica1 Method for Determining Wood Char-Layer at High Temperatures due an Anaerobic Heating, International Journ al olSalety and Security Engineering, 1, No. 1, 2011 , pp . 65-76 . Kamyar T., Wo1fgang W., Tamir P., Michael K., Steel reinforced timber structures for multi storey buildings, WCTE, World Conference Timber Engineering, 2012. White, R. H. , Dietenberger, M. A. , Fire Safety, Chapter 17, Wood Handbook: Wood as an Engineering Material, Forest Products Laboratory, 1999, USDA Forest Service. Poon, L., England, l P. , Literature Review on the Contribution ofFire Resistant Timber Construction to Heat Release Rate - Timber Development Association, Warrington Fire Research Aust. Pty. Ltd., pp.l -78, 2003, Project NO.20633 version 2b. Janssens, M. L., Modeling of the thermal degradation of structural wood members exposed to fire, Fire and MateriaIs , 28, 2004, pp. 199-207. Schaffer, E. L., Chan'ing rate of selected woods transverse to grain, Forest Products Laboratory, 1967, Madison (WI), Research paper FPL 69. White, R. H., Charring rates of different wood species, PhD dissertation, 1988, Madison University ofWisconsin, Madison (WI) , White, R, H" Erik V, Nordheim, E. V., Charring rate ofwood for ASTM E1l9 exposure, Fire Technol, 28, N" 1, 1992. Konig, l, Walleij, L., One-dimensional charring of timber exposed to standard and parametric fires in initially unprotected and postprotection situations. Swed Inst Wood Technol Res, 1999. Gardner, W. D., Syme, D. R., Charring of glued-laminated beams of eight austra1iangrown timber species and the effect of 13 mm gypsum p1asterboard protection on their charring, Sydney, 1991, N.S.W. Technical report nO.5, Co1lier, P. C. R., Charring rates oftimber, Branz, New Zealand, 1992, Study reporto Pun, C. Y. , Seng, H, K. , Midon, M. S. , Malik, A. R. , Timber design handbook. FRIM, 1997, Malayan Forest Records no.42. Cachim, P. B., Franssen, l M., Assessment of Eurocode 5 Charring rate Calculation Methods, Fire Technology, 46, 2010, pp. 169-18l. Nwosu, D. I , Kodur, V. K. R , Behaviour of stee1 frames under fire conditions, Cano J. Civ. Eng., 26, 1999, pp. 156-167. Joo-Saeng P., Jun-Jae L. , Fire Resistance of Light-framed Wood Floors Exposed to Real and Standard Fire, Journal 01 Fire Sciences, 22, 2004, pp. 449-471. Gandhi, P. D" Backstrom, R" Thermal and Mechanical Finite element modelling of Wood-Floor Assemblies Subjected to Furnace Exposure, Underwriters Laboratoires, USA, 2008, Project number: 07CA42520.

(16) 420 INTERNATIONAL CONGRESS FIRE COMPUTER MODELlNG 20. EN 1995-1-2:2004. Eurocode 5: Design oftimber structures, Part 1-2: General-Structural fire design, CEN, 2004. 21. EN 1993-1-2: 1995 . Eurocode 3: Design of Structures - Part 1-2: General Rules Structural Pire Design, CEN, 1995. 22. Holman, J. P., Transferência de Calor, 1983, McGraw-Hill, São Paulo. 23. EN 1991-1 -2:2002. Eurocode 1: Actions on Structures - Part 1-2: General actions Actions 011 Structures Exposed to Pire, CEN, 2002.

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