PARAMETRIC STUDY FOR SEISMIC RESPONSE OF DUAL STEEL FRAMES WITH DISSIPATIVE STEEL PANELS

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1 BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI Pulict de Universitte Tehnică Gheorghe Aschi din Işi Tomul LXI (LXV), Fsc. 3, 2015 Secţi CONSTRUCŢII. ARHITECTURĂ PARAMETRIC STUDY FOR SEISMIC RESPONSE OF DUAL STEEL FRAMES WITH DISSIPATIVE STEEL PANELS BY CĂLIN NEAGU *, FLOREA DINU nd DAN DUBINA Received: July 17, 2015 Accepted for puliction: July 31, 2015 Politehnic Univeristy Timişor, Romni Deprtment of Steel Structure nd Structurl Mechnics Astrct. Present study investigtes the prmetric response of dul steel frmes tht consist of steel plte sher wlls nd moment resisting frmes. The prmetric study ws crried out using numericl model which ws vlidted ginst experimentl tests. Sp2000 ws used to replicte the test results in order to vlidte the numericl models. The numericl model ws pplied to conduct incrementl dynmic nlyses on 6 story SPSW frme in order to determine its seismic response. In the nlysis two types of soil conditions nd seven different ground motion records were tken into ccount. The min ojective ws to estimte the ehviour fctor q, which is used in seismic design of such structures. Summry of investigtions nd min results will e presented. Key words: dul frmes; dissiptive pnels; nonliner dynmic nlysis; q fctor. 1. Introduction The structurl system using steel plte sher wlls (SPSW) for lterl resistnce hd mjor development worldwide with the introduction of design rules in North Americn nd Jpnese codes. The lck of design provisions in * Corresponding uthor: e-mil: clin.negu@upt.ro

2 62 Călin Negu, Flore Dinu nd Dn Duin Europen seismic code EN mde difficult the ppliction of the system. In the sence of such design provisions, other design codes (e.g. AISC 2010, (ANSI/AISC , 2010)) could e used s reference, ut this is not very strightforwrd. The economic cost nd construction efficiency of the system represent two dvntges of such structurl systems. The detiling of the infill pnel to ordering elements cn e done using fillet welds or olted connections. When olted connections re used, the construction time my e reduced nd there is possiility of plte replcement fter n erthquke. This represents recent development in the field, where dissiptive elements my e designed nd detiled to e replced fter n erthquke (Duin & Dinu, 2014). This requires specil design nd detiling conditions nd my reduce the cost of intervention for low to moderte erthqukes. In most cses, replcement is conditioned y the re-centering cpcity of the dul system. In order to ddress the issues presented ove with regrd to the performnces of SPSW systems, reserch progrm, including experimentl nd numericl studies, ws developed t Politehnic University Timisor, Lortory of Steel Structures. The experimentl study ws performed on dul SPSW systems in order to quntify the ehvior fctor q nd to evlute the recentering cpcity of the system. The numericl studies were performed on dul SPSW structures designed ccording to Eurocodes. Where necessry, AISC 2010 (ANSI/AISC , 2010) provisions were employed, lso. The study reported in this pper investigted the performnce of six story SPSW dul structure. The dul structurl system used is composed of moment resisting frme (MRF), two infill pnels which re connected to the oundry elements with olts, nd two dditionl stnchions tht re plced s interior verticl oundry elements (Fig. 1). This system llows the concentrtion of dmge minly in the pltes. If the flexile MR frmes re designed to remin elstic during the erthquke, they provide the restoring force tht is necessry to re-center the structure nd to llow the replcement of the dmged infill pltes. Infill pltes = + Stnchions Link em Fig. 1 Dul SPSW with MRF, infill pltes nd stnchions. Non-liner dynmic nlyses were employed tking into ccount two sets of ground motions scled for two types of spectr corresponding to soft nd

3 Bul. Inst. Polit. Işi, t. LXI (LXV), f. 3, stiff soil conditions given in EN The numericl models were clirted nd vlidted ginst experimentl dt (Duin & Dinu, 2014). 2. Prmetric Study 2.1. Design of Structure Design of the structure ws done ccording to Eurocodes (EN1998-1; EN ; EN ) nd AISC (ANSI/AISC , 2010). According to EN1998-1, the uilding site is chrcterized y pek ground ccelertion of 0.4 g, with corner period T C of 0.8 s (Type 1 response spectr nd ground type D). A ehvior fctor of 5 ws used for preliminry design of structure. The structure hs the configurtion presented in Fig. 2. Fig. 2 SPSW structure; equivlent structure with tension digonls. According to AISC Seismic Provisions (ANSI/AISC , 2010), SPSW is first pproximted y verticl truss with equivlent tension rces (Fig. 2 ). The cross sections of the equivlent rces need to e designed to meet the lterl drift requirements. According to the cpcity design principles from AISC (ANSI/AISC , 2010), the horizontl nd verticl oundry elements (HBE nd VBE) re designed to resist the mximum forces developed under the tension field ction of the fully yielded pnels. Axil forces, sher forces, nd ending moments develop in the SPSW oundry elements ecuse of the overll overturning, sher, nd tension field ction in the pnels. VBEs nd HBEs should remin essentilly elstic under the forces generted y fully yielded pltes, ut flexurl hinges re llowed t the ends of HBEs. To prevent excessive deformtion, leding to premture uckling under the pulling ction of the pltes, the minimum moment of inerti of the columns ws clculted. After the equivlent structure with the verticl truss ws designed nd configured, the rces were replced y steel pnels. For n ssumed ngle of inclintion α of the tension field (tken s 45 ) nd using the re of the equivlent rces, the thickness of the pltes ws clculted (Duin & Dinu, 2014).

4 64 Călin Negu, Flore Dinu nd Dn Duin The geometry nd section of frme memers re shown in Fig. 3. The exterior ys mesure 6 m, the interior y mesure 8 m nd hs two rced spns of 2.8 m long. IPE450 IPE500 IPE450 HEB400 2 mm HEB500 HEB400 HEB500 6 m m Fig. 3 Six story uilding frme. HEB m The story height is 3.5 m. The ems, stnchions nd columns were designed using S355 steel, which hs nominl yield strength f y of 355 N/mm 2. The pltes were designed using S235 steel, which hs nominl yield strength f y of 235 N/mm 2. Europen IPE nd HEB hot rolled profiles were used for ems, columns nd stnchions (see Fig. 3) Anlysis Procedure A non-liner incrementl dynmic nlysis (IDA) ws employed in order to estimte the seismic response of the SPSW system. Two type of soils were tken into ccount, i.e. soft soil (type D) nd stiff soil (type A) (Fig. 4), nd seven different ground motion records for ech type of soil. D A Fig. 4 Type 1 elstic spectrum ccording to EN

5 Bul. Inst. Polit. Işi, t. LXI (LXV), f. 3, Ech ground motion record ws scled to the liner-elstic 5%-dmped spectrl ccelertion etween 0.2T 1 nd T 1 (where T 1 is the fundmentl period of the structure) to mtch the trget spectrum (Type A nd D spectr, see Fig. 5). T 1 Ground motions T c=0.4s g=0.54g S=1.0 T 1 Ground motions T c=0.8s g=0.4g S=1.35 Fig. 5 Scled records: type A elstic spectrum; type D elstic spectrum. Note tht the first three periods of the structure re T 1 = 0.61 s, T 2 = = 0.18 s nd T 3 = 0.08 s. In the incrementl dynmic nlysis, the ground motion records were scled to severl intensities (using fctor λ) until the ttinment of numericl non-convergence (dynmic instility, DI) or other limiting criteri re ttined (e.g. exhustion of plstic deformtion cpcity in elements). Three performnce levels were considered, i.e. serviceility limit stte (SLS), where the intensity of ground motion is scled y λ = 0.5, ultimte limit stte (ULS) with intensity fctor λ = 1.0 nd collpse prevention limit stte (CPLS) with intensity fctor of λ = Vlidtion of Numericl Models The Finite Element Model used for the IDA nlysis is detiled y Duin & Dinu, (2014) nd (2013). The numericl model ws vlidted ginst experimentl test results. The test specimens were isolted from the second nd third story of 6 story dul SPSW frme structure with the configurtion presented in Fig. 1. Becuse of lortory restrictions, the specimens were downscled. The experimentl frme ws 3,500 mm height nd 4,200 mm wide (distnces mesured etween elements centerlines, Fig. 6 ). Slender steel pnels, with plte thickness of 2 mm, rtio L/tw mounting 595 nd spect rtio L/h of 0.8, were used. Typicl connections used for the experimentl specimens re presented in Fig. 6. Extended end plte olted connections were used to join ems nd columns. The joint ws considered rigid nd prtil strength (M j,rd =

6 66 Călin Negu, Flore Dinu nd Dn Duin = 0.9M,Rd ) (ccording to EN clssifiction) (Fig. 6 ). For the connection of the pltes to the oundry elements, 8.8 clss preloded olts nd 6 mm fish pltes were used. Additionl fishpltes of 4 mm were dded in order to strengthen the plte nd reduce the numer of olts (Fig. 6 c). HE240B Bolts 8.8 grde, M20 Finplte 120x6 Infill plte Strengthening plte c Fig. 6 Experimentl specimen; em-to-column joint; c plte to oundry elements connection. The specimen ws sujected to incresing cyclic loding until filure, ccording to ECCS loding protocol (Fig. 7 ) (ECCS 1985). Two ctutors with 360 mm stroke nd 1,000 kn nd 500 kn cpcity, respectively, were used, one t ech story (Fig. 7 ). To note tht monotonic test is first required for evluting the yielding displcement tht is used s loding prmeter in the cyclic test. Fig. 7 Loding protocol; Test set-up. Fig. 8 shows the monotonic () nd cyclic () response of the specimen in terms of se sher force versus top displcement. Due to the high plte slenderness (2 mm thickness), the sher uckling occurred t reltively low levels of drifts, t pproximtely 0.4%. After uckling, the lterl lod ws crried through the tension field developed in the pnel. The infill pltes yielded first t 0.9% inter-storey drift (Fig. 8, point ). The specimen could withstnd

7 Bul. Inst. Polit. Işi, t. LXI (LXV), f. 3, drifts of lmost 6% efore the drop in strength (point ).The numericl models hve een vlidted ginst the monotonic nd cyclic tests. The numericl model for monotonic nlysis predicted with good ccurcy the entire ehviour of the system, including the softening rnch, see Fig. 8. The smll differences cn e ttriuted to imperfections in testing set-up nd contriution of em to column connections (gusset plte effect). Using pivot hysteretic type hinges for strips, it ws possile to predict the overll cyclic ehviour lso, including the degrdtion of the pltes nd pinching effect, Fig Bse sher force [kn] Experimentl Numeric Top displcement [mm] Bse sher force, KN Fig. 8 Numeric vs. experimentl results Top displcement, mm Experimentl Numeric 2.4. Results One of the min prmeters ssocited with the glol performnce of the SPSW systems is the ehviour fctor q. The ehviour fctor q cn e expressed s product of the ductility reduction fctor, q μ, nd the over-strength fctor, q s. The over-strength my vry significntly nd is ffected y the contriution of grvity lods, mteril over-strength, structurl redundncy, etc. The ductility component q μ is defined s the rtio etween the ccelertion multiplier leding to collpse, λ u, nd the ccelertion multiplier leding to first yielding, λ 1. The ductility fctor is more importnt when the dissiption cpcity is of concern, nd will e further investigted. Fig. 9 to Fig. 12 show the development of plstic hinges nd the interstory drift rtios for the 6 story structure. In this pper is presented only the plstic mechnisms for the 2 nd nd 4 th ground motions (see Fig. 5), while the corresponding inter-story drifts re shown in comprison for the two types of soil conditions. In cse of 2 nd ground motion, t ultimte limit stte the plstic hinges re minly developed in pltes, with very smll dmge in moment resisting frme for soft soil conditions. This indictes tht the frmes remined in elstic domin nd poses the restoring force tht is required to re-center the structure

8 68 Călin Negu, Flore Dinu nd Dn Duin nd to replce the dmged pnels. At collpse prevention limit stte, the dmge is initited in the frme lso for oth type of soils, nd is lrger for soft soil conditions (see Fig. 9). SLS-A ULS-A CPLS-A SLS-D ULS-D CPLS-D Fig. 9 Plstic mechnism for 2nd ground motion: stiff soil; soft soil SLS-A ULS-A CPLS-A Story CPLS-D SLS-D ULS-D Inter-story drift, % Fig. 10 Inter-story drift rtio for the two types of soils (2 nd ground motion). In cse of 4 th ground motion, for stiff soil conditions the dmge is concentrted minly in pltes, frme does not present ny dmge until CPLS, indicting tht the structure hs re-centering cpcity (Fig. 11 ).

9 Bul. Inst. Polit. Işi, t. LXI (LXV), f. 3, SLS-A ULS-A CPLS-A SLS-D ULS-D CPLS-D Fig. 11 Plstic mechnism for 4 th ground motion: stiff soil; soft soil. In cse of soft soil conditions, plstic hinges re developed t ULS in pltes nd frme elements (em nd columns), which show tht the frme does not hve enough re-centering cpcity. (Fig. 11 ). For soft soil condition, the structure exhiits lrger drifts compred to stiff soil conditions (see Figs. 10 nd 12). One cn oserve n mplifiction of effects in cse of soft soil conditions (Type D spectrum), nd concentrtion of dmges in the lower hlf of the structure (Figs. 10 nd 12) SLS-A ULS-A CPLS-A Story 3 2 SLS-D ULS-D 1 CPLS-D Inter-story drift, % Fig. 12 Inter-story drift rtio for the two types of spectr (4 th ground motion).

10 70 Călin Negu, Flore Dinu nd Dn Duin Tle 1 present the plstic rottions in hinges developed in ems (B) nd columns (C) t the three limit sttes for the two ground motions presented ove (2 nd nd 4 th ). Tle 1 Plstic Hinges Vlues for the Two Ground Motions Soil Level 2 nd cc. 4 th cc. B C B C SLS A ULS CPLS SLS B ULS CPLS DI DI DI DI Note: B ems; C- column; DI dynmic instility. Fig. 13 shows the incrementl dynmic nlysis curves in terms of inter-story drift rtios nd ccelertion multipliers for the structure for the two types of soil conditions considered in this study. In cse of ground motions scled to type D spectrum, the structure ttins the collpse criteri efore reching collpse prevention limit stte for 3 ground motions (2 nd, 4 th nd 7 th ). In cse of ground motions scled to type A spectrum, the structures ttin the collpse criteri well fter collpse prevention limit stte. Tle 2 shows the individul vlues for ech ground motion nd the verge vlue of the ductility component, q μ, per type of spectrum. For stiff soil conditions (type A spectrum), the verge vlue of the ductility fctor is 4.0, while for soft soil conditions (type D spectrum), q μ mounts 3.6. The type of ground motion influences the yielding nd the ultimte vlue of the ccelertion ut the effect on q μ fctor is not very significnt. A soil D soil 6 th 5 th 3 rd 6 th 1 st 1 st 4 th 2 nd 7 th 3 rd 7 th 5 th 4 th 2 nd Fig. 13 IDA curves for ground motions scled to type A nd D spectr.

11 Bul. Inst. Polit. Işi, t. LXI (LXV), f. 3, Tle 2 q μ Vlues Soil Prm. 1st 2nd 3rd 4th 5th 6th 7th Averge λ A λ u q λ D λ u q To note tht, if the verge vlues of the ductility fctor re multiplied with the over-strength fctor q s = 1.5 used in design, the resulting vlue of ehviour fctor q is round 6, which indictes tht the SPSW system hs good ductility nd my e designed considering the high dissiption concept. 3. Conclusions An extensive numericl simultion progrm using incrementl nonliner dynmic nlysis ws employed on 6 story dul SPSW structure with link ems nd rigid em-to-column connection, in order to evlute the ehviour fctor q. A set of seven ground motions nd two types of soil (i.e. stiff nd soft soil) were tken into ccount. The results of the numericl nlyses showed tht the type of ground motion ffects the response of SPSW structures. The dmge in structure is more severe in cse of soft soil conditions. The vlues of q fctor otined in the numericl study re closed to those reported experimentlly (Duin & Dinu, 2014) nd confirm tht SPSW structures cn e clssified s highly dissiptive structures. However, further studies re required for complete vlidtion of ehviour fctor q. Acknowledgement. This work ws prtilly supported y the strtegic grnt POSDRU/159/1.5/S/ (2014) of the Ministry of Ntionl Eduction, Romni, co-finnced y the Europen Socil Fund Investing in People, within the Sectorl Opertionl Progrmme Humn Resources Development REFERENCES Duin D., Dinu F., Experimentl Evlution of Dul Frme Structures with Thin Wlled Steel Pnels. Thin Wlled Structures, 78, Duin D., Dinu F., Experimentl Evlution of Dul Frme Structures with Thin- Wlled Steel Pnels. Thin-Wlled Structures, 78, 57 69, 2013.

12 72 Călin Negu, Flore Dinu nd Dn Duin Negu C., Multi-Storey Building Frmes Stiffened with Dissiptive Sher Wlls. Ph. D. Diss., Univ. Politehnic Timişor, Romni, Vmvtsikos D., Cornell C.A., Incrementl Dynmic Anlysis. Erthquke Engng.. Struct. Dynm., 31, 3, (2002). * * * ANSI/AISC , Seismic Provisions for Structurl Steel Buildings. Amer. Inst. for Steel Constr., * * * ECCS 1985, Recommended Testing Procedures for Assessing the Behvior of Structurl Elements under Cyclic Lods. Europen Convention for Constructionl Steelwork. Technicl Committee 1, TWG 1.3 Seismic Design, No.45, * * * Eurocode 3: Design of Steel Structures. Prt 1-1: Generl Rules nd Rules for Buildings. EN , CEN, * * * Eurocode 8: Design of Structures for Erthquke Resistnce. Prt 1: Generl Rules, Seismic Actions nd Rules for Buildings. EN , CEN, * * * Eurocode 3: Design of Steel Structures. Prt 1-8: Design of Joints. EN , CEN, STUDIU PARAMETRIC PENTRU RĂSPUNSUL SEISMIC AL CADRELOR DUALE DE OŢEL CU PANOURI DISIPATIVE DIN OŢEL (Rezumt) Se investigheză răspunul prmetric l cdrelor dule de oţel formte din cdre necontrvântuite şi pnouri de forfecre din oţel (SPSW). Studiul prmetric fost efectut folosind un model numeric vlidt cu jutorul unor teste experimentle. Sp2000 fost folosit pentru clir rezulttele testelor în vedere vlidării modelului numeric. Acest model fost folosit pentru efecture unor nlize dinmice incrementle pe un cdru SPSW cu 6 nivele în vedere determinării răspunsului seismic. În ceste nlize u fost lute în considerre două tipuri de teren şi şpte ccelerogrme diferite. Oiectivul principl l- constituit estimre fctorului de comportre q, cre este folosit în proiectre seismică curentă l cestui tip de structuri. Rezulttele principle sunt prezentte pe scurt.