Aville online t www.sciencedirect.com ScienceDirect Procedi Engineering 19 (217 ) 237 242 Structurl nd Physicl Aspects of Construction Engineering Numericl Anlysis of Steel Portl Frme Exposed to Fire Lenk Lusov *, Ivn Kolos, Vldimir Michlcov, Ivet Skotnicov VŠB-Technicl University of Ostrv, Fculty of Civil Engineering, Ludvík Podéště 1875/17, 78 33, Ostrv, Czech Repulic Astrct The pper presents numericl comprtive study which is concerned with the ehvior of steel hollow section portl frme exposed to elevted tempertures while considering the effect of oth therml nd structurl responses incorporting mteril nd geometric nonlinerities. The work provides study of deformtions nd es ffecting the filure ehvior of solved portl frme. The filure temperture is evluted while respecting vrile mteril chrcteristics in time of growing temperture. This work presents n investigtion of the portl frme with the uniform nd non-uniform temperture distriution over the height of the rfter using finite element softwre SCIA Engineer. 217 The Authors. Pulished y Elsevier y Elsevier Ltd. This Ltd. is n open ccess rticle under the CC BY-NC-ND license (http://cretivecommons.org/licenses/y-nc-nd/4./). Peer-review under responsiility of the issue editors. Peer-review under responsiility of the orgnizing committee of SPACE 216 Keywords: Portl steel frme; fire; filure mechnism; FEM; numericl modeling 1. Introduction This pper presents prmetric study of the steel portl frme exposed to fire. Behviour of the frme structure exposed to fire depends on the restrint t memer ends nd the degree of force redistriution during fire development. The vlid stndrds for fire design sitution llow using simplified methods of clcultion sed on empiricl formule for therml nlysis of structures [1]. These ssumptions my result in solutions, which cn e suitle for structurl element clcultions, ut my not e enough e.g. for structures where elevted temperture cuses dditive internl forces due to restrined conditions. In these cses, dvnced clcultions must e crried out. It is very importnt to mke comprison with experimentl testing, which used to e very difficult nd expensive. In the clcultions of structures exposed to elevted temperture the effect of oth therml nd structurl responses incorporting mteril nd geometric nonlinerities must e considered. The temperture distriution in section is otined in therml nlysis nd the -strin stte of structure t the time of growing temperture is solved in * Corresponding uthor. Tel.: +42-596-732-1326. E-mil ddress: lenk.lusov@vs.cz 1877-758 217 The Authors. Pulished y Elsevier Ltd. This is n open ccess rticle under the CC BY-NC-ND license (http://cretivecommons.org/licenses/y-nc-nd/4./). Peer-review under responsiility of the orgnizing committee of SPACE 216 doi:1.116/j.proeng.217.5.332
238 Lenk Lusov et l. / Procedi Engineering 19 ( 217 ) 237 242 sttic nlysis. Furthermore, vrile vlues of mteril properties, which depend on temperture, must e tken into ccount [2]. Some results from the nturl fire Crdington tests re descried in prmetric studies [3,4], where the influence of the end-restrints of steel ems nd the prolem of locl uckling re highlighted. Numericl studies [5,6] show differences in therml field in the hollow nd open cross sections nd show the importnce of determining the exct temperture distriution in the section of restrined structures. 2. Frme structure Numericl studies deling with structures exposed to fire used to e crried out using specil softwre progrms intended for fire nlysis. The ide of the uthors is to nlyze the prolem of steel structures exposed to fire in the widely distriuted commercil softwre nd to compre the results with specil softwre intended for fire nlysis. In this study the portl hollow section frme exposed to elevted temperture is solved in SCIA Engineer nd the results re compred with the nlysis mde y the softwre SAFIR in [7]. Both softwre re sed on FEM. In this pper, the uthors intend to void the prolem with the uckling of the lower flnge in fire [4] due to the hollow section nd the prolems of the end-restrints, therefore is supposed to e protected rigid em-column connection. In this pper, inner forces nd norml from mteril nd geometricl liner nd nonliner solutions re evluted. This study evlutes the filure temperture predicted through the suggested filure criterion. This study is lso sed on uthors experimentl testing crried out in the therml technicl chmer t the fculty of Sfety engineering in 212 with the steel hollow section frme structure with fixed supports [5] where the formtion of plstic hinges ws monitored. 2.1. Sttic schem nd loding Fig. 1. Sttic schem of portl frme nd heted cross-sections. Sttic schem of the portl frme cn e seen in Fig. 1. The unprotected frme consists of two columns with fixed ends nd rfter with inclintion = 11, ll of the hollow cross-section 25/1. The rfter of the frme is loded with uniformly distriuted mechnicl lod of g = 1 kn/m, which remined constnt throughout the structurl nlysis. The frme is lso sujected to fire lod ccording to the stndrd ISO-834 fire curve [1]. Two cses of temperture lod re solved. In the first cse (frme A, Fig. 1) there is supposed to e uniformly heted columns nd rfter. In the second cse (frme B, Fig. 1) the columns re heted from ll sides nd the rfter from three sides. Comprtive study [7] did not show clerly whether it ws used in the clcultion non-uniformly distriuted temperture over the height of the rfter, or whether roof pnels lid directly on the frme structure nd cooled it from ove. Therefore, in this study there re solutions for oth cses (frme A, frme B).
Lenk Lusov et l. / Procedi Engineering 19 ( 217 ) 237 242 239 2.2. Numericl model The sttic nlysis is solved in SCIA Engineer softwre sed on FEM [8]. There were two models of frme mde in SCIA - 2D em model nd 3D shell model. The 2D finite element model of the frme is formed with 8 em finite elements. The 3D finite element model of the frme consists of 9436 isotropic thick shell elements. The roof sl is not prt of the model in SCIA s it only provides therml oundry condition for the temperture. 2.3. Boundry conditions The temperture of the structure is derived y normtive reltions for het trnsfer from gs temperture (ISO-834) in time of fire [1]. Therml oundry conditions for the upper flnge of the rfter of the frme B re tken from ANSYS softwre ccording to the verified experiment descried in [5,6], where the importnce of clcultions of temperture distriution t hollow sections t restrined structures is highlighted. The model in ANSYS nd temperture distriution in the section cn e seen in Fig. 2. Fig. 2. Temperture distriution in the section of the frme B in time of fire: () t = 9 minutes; () t = 15 minutes. Fig. 2, show the comprison temperture grdient within the rfter cross-section in time of fire t = 9 minutes when temperture of the exposed prt of the section is 3 C nd lso in time of fire t = 15 minutes when the temperture of the exposed side is 5 C. The verge temperture of the top flnge otined from therml nlysis is input into the clcultions in SCIA nd lso corresponding mteril chrcteristics. Fig. 3. Therml loding () frme A; () frme B. Fig. 3 shows the grph of the therml loding. Gs temperture curve is given y the stndrd ISO-834 fire curve [1]. The other curves represent therml loding of the structure. The higher temperture curve (Fig. 3) elongs to the temperture of the exposed sides of the frme nd the lower temperture curve elongs to the upper flnge of the rfter of the frme B.
24 Lenk Lusov et l. / Procedi Engineering 19 ( 217 ) 237 242 2.4. Mteril properties The mechnicl mteril properties of the exmined structure t mient tempertures re: f y = 235 MP, nd Young's modulus of elsticity E = 21 GP. Therml nd physicl mteril properties of steel re nonlinerly temperture dependent nd in the clcultions followed the description ccording [9]. Chnging therml mteril properties re used in the therml nlysis in ANSYS nd chnging mechnicl properties re used in SCIA clcultions in the structurl nlysis. 3. Results of the prmetric study Mteril nd geometric liner nd nonliner clcultions [1] re provided in this study. The swy mechnism [5,7] formtion of plstic hinges is expected in the frme nd in the column s se. Results re elorted grphiclly in Fig. 4-7. Grphs in Fig. 4 nd 5 compre developed mteril nd geometric liner nd nonliner solutions of norml in 2D nd 3D model in monitored plces. Fig. 4 shows the results of the frme A nd Fig. 4 shows the results of the frme B. Quite different results cn e seen. Plstic hinges on frme A re formed t 6 C (t = 19 min.) in the nd lso t the se. There is possiility on frme B of formtion of the first plstic hinges in the frme erlier (3 C, time t = 9 minutes) due to the non-uniform temperture in the rfter, plstic hinges in the se re formed in the temperture 6 C (t = 19 minutes). The first plstic hinges ccording to the comprtive study [7] would ecome t 467 C in the nd the second plstic hinges t 556 C in the column s se, so results from SCIA Engineer show similrity with the comprtive study [7]. Norml [MP] -5-1 -15-2 -25 se se Norml [MP] -5-1 -15-2 -25 se se Fig. 4. Norml in nd column s se - nonliner solution: () frme A; () frme B. Norml [MP] -5-1 -15-2 -25 se se Norml [MP] -5-1 -15-2 -25 se se Fig. 5. Norml in nd column s se - liner solution: () frme A; () frme B.
Lenk Lusov et l. / Procedi Engineering 19 ( 217 ) 237 242 241 Slight differences in the results might rise due to the different therml oundry conditions of the structure or different settings in the nonliner clcultions in the softwre. Fig. 6 shows the results of the developed deflection t mid-spn of the rfter in the frme A nd B from mteril nd geometricl nonliner solutions. Fig. 7 shows the results of the developed ending moment in the frme nd xil force in the rfter on frme A nd B from 2D em model. All results show similrities with the comprtive study. Deflection t mid-spn [mm] 1-1 -2-3 -4-5 -6-7 -8 Uz elst Uz elst Uz plst Uz plst Deflection t mid-spn [mm] 1 5-5 -1-15 -2-25 -3 Uz elst Uz elst Uz plst Uz plst Fig. 6. Deflection t mid-spn of the rfter nonliner solution: () frme A; () frme B. Bending moment [knm] 1 5-5 -1-15 My - uniform My - uniform se My - nonuniform My - nonuniform se Axil force in rfter [kn] -1-2 -3-4 -5-6 -7-8 -9 N - uniform temp. N - nonuniform temp. Fig. 7. () Bending moment development in the nd in the se of the column; () rfter xil force. Fig. 8. Detil of norml distriution on the frme B in MP: () frme, t = 9 minutes; () column s se, t = 19 minutes.
242 Lenk Lusov et l. / Procedi Engineering 19 ( 217 ) 237 242 Fig. 8 shows detils of the frme B nd formtion of plstic hinges in time of fire t = 9 minutes, temperture of the rfter is 3/185 C, the limit of the mteril is the sme s t the mient temperture f y = 235 MP. Fig. 8 shows detil of the frme B in column s se in time of fire t = 19 minutes, temperture of the rfter is 6/45 C, limit for reched temperture 6 C drops to the vlue f y = 11 GP. 4. Conclusions A comprtive study etween the results of the proposed model from SAFIR softwre nd the results from the softwre SCIA Engineer re presented in the pper. The study shows developed deformtions nd es ffecting the filure ehvior of the solved portl frme in time of fire nd the following conclusions cn e drwn: The comprison etween the two different softwres gree. The softwre which is not intended for generl fire nlysis cn e used for the dvnced numericl clcultions of structures exposed to fire if there re respected chnges of mteril chrcteristics under fire nd lso the effect of growing temperture in the restrint structures. In this study, models in 2D nd 3D show similr development of the exmined vriles, the filure temperture is 6 C which corresponds with the time t = 19 minutes ccording to the stndrd fire curve. The results show different formtion of plstic hinges depending on whether the hollow section frme rfter is heted from three sides or from ll sides. Therml nlysis is very useful for getting the exct temperture distriution long the height of the section especilly t the eginning of the fire when the effect of non-uniform temperture could e more importnt thn in the lter stges of the fire. Acknowledgements Finncil support from VŠB-Technicl University of Ostrv y mens of the Czech Ministry of Eduction, Youth nd Sports through the Institutionl support for conceptul development of science, reserch nd innovtions for the yer 216 is grtefully cknowledged. References [1] Hndook 5: Design of Buildings for the Fire Sitution, Book y Leonrdo d Vinci Pilot Project CZ/2/B/F/PP-1347, 25. [2] J. Králik. A RSM pproximtion in proilistic nonliner nlysis of fire resistnce of technology support structures, Advnced Mterils Reserch, 969 (214), pp. 1-8. DOI: 1.428/www.scientific.net/AMR.969.1. [3] A. Sntigo, L.S. d Silv, P.V. Rel, M. Veljkovic, Numericl study of steel su-frme in fire, Computers nd Structures 86 (28)1619-1632. [4] F. Wld, L.S. d Silv, D. Moore, T. Lennon, M. Chldn, A. Sntigo, et l. Experimentl ehviour of steel structure under nturl fire. Fire Sfety J 41 (7) (26), 59-22. [5] L. Lusov, V. Michlcov, I. Skotnicov, P. Konecny, Effect of Non-Uniform Temperture Distriution over the Cross-Section in Steel Frme Structure, 215, 1.428/www.scientific.net/AMM.769.65. [6] L. Lusov, I. Skotnicov, J. Brozovsky, Numericl Anlysis of Effects of Fire to Steel Frme Structures, in: The Twelfth Interntionl Conference on Computtionl Structures Technology, Itly, 214, DOI: 1.423/ccp.16.2. [7] M.M.El-Heweity, Behvior of portl frmes of steel hollow sections exposed to fire, Alexndri Engineering Journl (212) 51, pp. 95-17. [8] T. Liu Finite-element modeling of ehviors of steel rfters nd connections in fire, Journl of Constructionl Steel Reserch, 36 (3) (1996), pp. 181 199. [9] EC3-Eurocode3: Design of steel structures. Prt 1 2: Generl rules-structurl fire design, Brussels, Belgium, 25. [1] J.B. Schleich, J.C. Dotreppe, J.M. Frnssen, Numericl simultions of fire resistnce tests on steel nd composite structurl elements or frmes, in: Proc., 1st Int. Symp., Fire Sfety Sci., Interntionl Assocition for Fire Sfety Science, Boston, 1985, pp. 311 323.