Available online at ScienceDirect. Procedia Engineering 172 (2017 )

Transcription

1 Aville online t ScienceDirect Procedi Engineering 172 (217 ) Modern Building Mterils, Structures nd Techniques, MBMST 216 Adhesive onding in steel construction - Chllenge nd innovtion Yvonne Ciupck *, Hrtmut Psternk, Christoph Mette, Eliseth Stmmen, Klus Dilger Chir of Steel nd Timer Structures, BTU, Konrd-Wchmnn-Allee 2, 346 Cottus, Germny Institute of Joining nd Welding, Technische Universität Brunschweig, Lnger Kmp 8, 3816 Brunschweig, Germny Astrct Despite much dvncement of typicl joining techniques in steel construction, fundmentl prolems, like residul stresses for welds s well s wekening of the cross section for olts nd screws, still remin. The ppliction of onded joints could improve the sitution. The utomotive industry shows the potentil of this certin joining technique since yers. Even in civil engineering nd especilly in steel construction, reserchers re continuously estlishing the onding technology s structurl element. On the one hnd onded joints men chllenge, ut on the other hnd n innovtion, wht is shown in this pper. 217 Pulished y Elsevier Ltd. This is n open ccess rticle under the CC BY-NC-ND license 216 The Authors. Pulished y Elsevier Ltd. ( Peer-review Peer-review under under responsiility responsiility of the of orgnizing the orgnizing committee committee of MBMST of MBMST Keywords: Adhesive; joining technology; steel structure. 1. Chllenge 1.1. Design of ondline geometry A gret numer of dhesives with different crrying nd deformtion ehvior, s well s vrying hndling properties re ville for the design of onded structures. Due to generl lck of experience the selection of suitle dhesive systems is difficult tsk for civil engineer. Generl requirements for n dhesive re chrcterized y specific viscosity for the mnufcturing nd sufficient crrying nd deformtion cpcity of the ondline. Despite these prmeters the properties of the dherent surfce ply n importnt role for the compound. * Corresponding uthor. Tel.: ; fx: E-mil ddress: yvonne.ciupck@-tu.de Pulished y Elsevier Ltd. This is n open ccess rticle under the CC BY-NC-ND license ( Peer-review under responsiility of the orgnizing committee of MBMST 216 doi:1.116/j.proeng

2 Yvonne Ciupck et l. / Procedi Engineering 172 ( 217 ) Thus, clening nd degresing of steel surfces re essentil during the onding process. In ddition, mechnicl pre-tretments such s lsting cn improve the dhesion properties. Uniform lod Sher: "suitle" Pressure: "suitle" Tension: "less suitle" Uneven nd cominted lod Sher nd peel: "d" peel: "d" clevge: "d" Fig. 1. Influence of geometric design nd loding of ondline. Moreover, the kind of loding hs ig influence on the crrying cpcity of onded steel construction. Uneven nd comined lods s well s peel stresses should e voided, s shown in Fig. 1. But uniform distriuted tension, pressure nd sher impcts re suitle. By slopping the dherent ends stress peks cn e reduced, which increses the crrying cpcity of the onded connection Crrying nd deformtion ehvior of onded constructions The crrying nd deformtion ehvior of ondlines is nonliner nd time dependent. According to the kind of dhesive sis distinct creep nd relxtion effects cn e oserved. The long-term mechnicl ehvior is influenced y environmentl effects, e.g. temperture, UV-rdition nd humidity. These impcts cn led to irreversile degrdtion of the mechnicl ondline properties. Prticulr ttention is pid to the temperture dependency, ecuse dhesives re chrcterized y so-clled glss trnsition temperture. If ondline is exposed to high therml impcts, higher thn the glss trnsition, it shows incresed deformtions nd decresed ultimte stress. Low tempertures led to high stiffness nd n incresed notch sensitivity of the ondline. These reltions cn e utilized in ppliction, e.g. elstic dhesives nd seling mterils re used for tempertures higher thn the glss trnsition to void therml residul stresses nd compenste therml strins. Becuse of the complexity of the crrying nd deformtion ehvior, n pproprite description of the stress distriution in ondline mens complex clcultions, e.g. numeric simultions. Since simple nd stndrdized concepts re necessry for the design in civil engineering, the development of suitle nlyticl models poses specil chllenge. Fig. 2. () Butt joint test; () Lp sher test. Another importnt chllenge is the determintion of chrcteristic mteril prmeters for the design of ondlines. Wheres the temperture dependency of mteril properties for steel dherents need only to e considered for fire design, it is not sufficient for dhesives. The detection of time dependent mteril prmeters, y considertion of dmging environment impcts, is impertive. But currently, only simple test methods re ville, which exclute the implementtion of suchlike influence fctors. On the one hnd the sher-stress to sherstrin reltion cn e descried with sher lp tests ccording to DIN EN [1]. On the other hnd evidence out the crrying ehvior of ondlines under norml stress sttes cn e otined from utt joint tests ccording to DIN EN 1587 [2]. The specimens nd loding sitution for these experimentl investigtions re shown in Fig. 2.

3 188 Yvonne Ciupck et l. / Procedi Engineering 172 ( 217 ) With these destructive tests, the ondline properties cn e chrcterized, ut initilly without considertion of time nd environment dependent effects. Interction reltions cn e deduced from multi-xil tests, such s rcn-tests. The offhnded trnsfer of knowledge from these smll scle specimen tests to typicl steel construction dimension is not possile, so specimen component tests still remin necessry. 2. Innovtion 2.1. Appliction of onding technology for fçde construction The Chir of Steel nd Timer Structures of the Brndenurg University of Technology dels with two ppliction exmples of onding technology in different reserch ctivities. A onded connection of trpezoidl fçde nd onded reinforcement of hollow section, for typicl trnsom-mullion-fçde, re investigted. Fçdes with trpezoidl sheets re deployed predominntly for light weight hlls nd industry constructions. After the erection of steel skeleton s the primry structure, sustructure of light weight steel profiles is instlled, fcilittes the connection of the trpezoidl sheets y screws or crtridge-fired pins. This joining method with fsteners wekens the cross section nd cn led to indvertent dents, scrtches or holes in the fçde view. In ddition, the self clening effect is dysfunctionl in the re of slient fstener heds. Due to these prolems of typicl joints, the possiilities of indirect onded fçde connection hve een developed, which re shown in Fig. 3. The connection concepts re designed so tht ded lods re crried y specil lod ppliction points t the top of the fçde. Thus, creep effects of the ondline re voided. Specilly formed connection profiles in ddition to olt connection, relized with n elongted hole, llow the deformtion of the outer shell without introducing constrins into the ondline. cover outside sel isoltion glss L-profile T-profile -profile em screw self-drilling inside reinforcement ondline Fig. 3. () Structures for onded fçde connections with different shpe of connection profile; () Bonded fçde reinforcement. Principl requirements of rchitects nd contrctors for representtive uildings re high side view trnsprency, structured nd light filled fçdes. In lot of cses the trnsom-mullion-construction is relized, so in order to chieve the desired impression, it is necessry to put the primry structure in the ckground. Tht requires minimiztion of the outer dimensions y incresing the stiffness of the structured memer t the sme time. An innovtive solution is offered y the dhesive onding technology. With steel reinforcement, onded to the inside of typicl hollow section, new type of compound cross section with n incresed stiffness nd crrying cpcity is creted (Fig. 3). The dvntge of reinforced trnsom-profile compred to hollow section with higher thickness is the lesser slenderness of the wes, thus voiding the uckling of wes under pressure. The principle of fçde hollow profiles with n inner reinforcement is similr to glued lminted timer, ut in contrst to timer structure, ondline design nd evidence is necessry, due to the higher stiffness of the steel dherents. The presented constructions re developed so tht ll onded connections cn e relized in lortory under controlled conditions. Non-reproducile ondlines nd onding on the side re voided nd the pre-prepred elements cn e mounted on site. The joining with dhesives is introduced s n dditionl process step, without chnging the estlished principles nd methods of fçde construction.

4 Yvonne Ciupck et l. / Procedi Engineering 172 ( 217 ) Experimentl investigtions of onded steel constructions under sttic loding Force [N] Deformtion [mm] Fig. 4. () Test setup; () Test results. The ppliction exmples from Fig. 2 were experimentlly investigted, in order to determine the lod nd deformtion ehvior, s well s to deduce Eurocode-sed design concept [3]. A strip coted trpezoidl profile with thickness of 1 mm ws used for the fçde connection, nd simplified L-profile with thickness of 2 mm ws chosen to crete the connection profile. With two-component copolymer sed dhesive ondline thickness of 2 mm ws set. The surfce ws pretreted y lsting with rounded cut wire to improve the dhesion properties of the steel dherents. The experimentl set up, shown in Fig. 4 ccurtely represents the conditions in the mounted stte of the fçde connection, ecuse the generl impct results from wind, cting perpendiculr to the ondline. During the conduction of the displcement-controlled test, the ends of the trpezoidl element were rced ginst the mchine tle. All joints filed with cohesive filure nd ehved strongly non-liner (Fig. 4). The ondline llows lrge deformtions, which is positive in regrd to dvnce notice of filure. Specific experimentl investigtions were crried out, in order to evlute the structurl ehvior of the fçde reinforcement. A typicl hollow section with width of 6 mm, height of mm nd wll thickness of 2.5 mm ws chosen. Due to the interesting ondline filure, which should e investigted in the tests, the profile length ws set to 1 m, sed on pilot tests nd nlyticl nlysis. With specil pneumtic method, which ws developed for this ppliction exmple, sheet metl steel (width: 5 mm; height: 2 mm) ws onded to the inner side of the hollow profile. The pre-tretment of the specimens ws defined y lsting the reinforcement with rounded cut wire, s well s clening nd refining ll surfces with cetone. To ccurtely reflect the instll conditions, the lod ws trnsferred to the specimen y two doule sher connections t every lod ppliction point nd t the supports. These points were designed to llow tension-free horizontl deformtions nd rottions. 3 w F/2 2 w F/2 w 1 F w F/2 w 1 F 2 w 3 A w A F/ Cross section A-A Force [kn] , 2, 4, 6, 8, Deformtion in xis [mm] Fig. 5. () Four point ending test; () Test results.

5 19 Yvonne Ciupck et l. / Procedi Engineering 172 ( 217 ) The evlution of the experiment shows tht the ondline of ll specimens filed with cohesive filure. During the tests distinct leveling of the ultimte lod ws oserved, which develops with the ondline filure. Compred to reference specimen without reinforcement (dshed line in Fig. 5), n improvement of stiffness nd crrying cpcity cn e deduced Design of onded joints in steel structures In previous reserch project [3] Eurocode-sed design rules for the presented ppliction exmples were developed. This ws relized y juxtposition of test results with solutions of nlyticl models, which re descried in [4]. The min ide of this procedure is to seprte the onded joint into theoreticl components, which cn e treted seprtely. Bsed on the wekest-link-pproch, the crrying cpcity of the connection or compound cn e expressed y the smllest vlue of clculted resistnces of the ondline nd the steel dherents. Herein the ondline is modeled y spring elements, which cn e chrcterized y smll scle specimen tests (see chpter 1.2), representing the specific loding sitution of the ppliction exmple. The principle of the component model is shown in Fig. 6. Fig. 6. Component spring model. Meinz [4] developed two nlyticl models to descrie the crrying ehvior of the presented pplictions, sed on the theory of elstic supported sls. He ssumed the properties of ondline to e expressed y chrcteristic vlues of tension strength ( k), sher strength ( k), Young s modulus (E k) nd sher modulus (G k). These prmeters were determined y utt joint nd lp sher tests (see Fig. 2) ccording to the Eurocode requirements nd re summrized in tle 1. Tle 1. Chrcteristic mteril properties of different dhesives [N/mm²]. Adhesive sis E k k G k k Copolymer Epoxy In ccordnce to the regultion of the Eurocode concept [5], semi-proilistic studies for oth models were crried out. The min ojective ws to determine prtil sfety fctors M for the resistnce models nd to introduce so-clled conversion fctors to tke into ccount temperture dependent ( t) nd mnufcturing dependent effects ( m). Regrding the cohesive ondline filure mode, the design vlue of the resistnce cn e expressed with Eq. (1). Rk Rd t m i M (1) The clirtion process resulted in prtil sfety fctor for the onded fçde connection of 2.16 nd for the fçde reinforcement of These vlues re sed on defined reference conditions during the test, which re ssumed to e 2 C nd 2 mm ondline thickness for the elstic copolymer or.2 mm for the epoxy resin sed dhesive. To consider influences from temperture or chnges of the thickness of the dhesive lyer, smll scle tests were repeted while vrying certin test conditions. To determine the conversion fctors, proilistic

6 Yvonne Ciupck et l. / Procedi Engineering 172 ( 217 ) conceptions with respect to proility functions re employed. The distriution function of resistnce must e formulted depending on the vriles temperture nd ondline thickness. This procedure results in conversion fctors, which re summrized in tle 2 for temperture dependent effects nd in tle 3 for mnufcturing dependent influences. Tle 2. Conversion fctors for temperture dependent effects. t Copolymer Epoxy -2 C T 2 C 2 C < T 8 C -2 C T 2 C 2 C < T 8 C Sher Tension Tle 3. Conversion fctors for mnufcturing dependent effects. m Copolymer Epoxy 2 mm d k 5 mm.2 mm d k.5 mm.5 mm < d k 2 mm Sher Tension As shown within the results, the investigted effects depend on the type of loding. Consequently different conversion fctors for norml nd sher stress conditions re recommended. Due to the strong decrese of the mteril prmeters t high tempertures nd different ondline thicknesses, the conversion fctors re declred for specific rnges Adhesive onded steel structures under cyclic loding As mentioned efore, the performnce of dhesive onded joints depends on time nd environment influences. The crrying nd deformtion ehvior of ondline is chrcterized y creep nd relxtion effects, ffected y temperture nd permnently chnged y geing processes. The ojective of n ongoing reserch project is to crry out cyclic test procedures for the presented ppliction exmples, tking into ccount these polymer specific properties [6]. In first step, representtive lod functions for the test sequences re deduced from rel mesured dt. Becuse the studied fçde connection is minly stressed y wind nd temperture, this investigtion focuses on environmentl dt from different wether sttions in Germny. The extreme tempertures for specific period, s well s the vrition of therml impcts over time, re determined y sttisticl mens. For the deduction of the fçde temperture sed on mesured ir temperture, different thermo-physicl effects, such s rdition nd convection, re considered nd shown in Fig. 7. The otined vlues from this simultion descrie temperture rnge from -2 C to 8 C, in greement with Eurocode 1 [7] nd the uilding code for externl wlls [8]. Direct nd diffuse solr rdition Forced convection Outside Inside Free convection Het rdition Het rdition Het pssge Fçde temperture [ C] Jn Fe Mr Apr My June July Aug Sept Oct Nov Dec Fig. 7. () Fçde temperture influencing prmeters; () Sttisticlly determined temperture lod cycle.

7 192 Yvonne Ciupck et l. / Procedi Engineering 172 ( 217 ) A suitle loding cycle (see Fig. 7) ws determined sed on sttisticl studies regrding n hourly pproch. The minimum temperture is ssumed to e -2 C (dshed line in Fig. 7) ccording to the code requirements [7]. Thus, for every month so-clled model dy is provided, which rnges from the minimum to the mximum temperture. The curve in Fig. 7 shows the vrition of therml impcts during the monthly model dy. During the experimentl investigtions model dy needs to e repeted, ccording to the numer of dys month. Moreover, test procedure for simultion of wind loding is extrpolted from ctul mesured wind speed dt. Due to the comintion of the typicl wind lod y qusi-sttic men nd turulent time-dependent prt, the test cycle ws developed from mesurements with vrious smpling rtes. To descrie the time stedy wind lod, the 1 minute men vlue of the windiest Germn wether sttion in Helgolnd (from the rchive of Deutscher Wetterdienst ) is used. This is comined with the wind turulences mesured in Krlsruhe [9] with smpling rte of 1 Hz. The composite wind speed function is trnsferred to lod to numer-of-cycles function for 1 m wide qudrtic uilding, s model fçde. In the frmework of the project, this specific function ws nlyzed y the rinflow method, which results in n mplitude collective for wind lod shown in Fig. 8. Amplitude [N] Numer of cycles, cumultive [-] Fig. 8. Amplitude collective for wind lods. The im for the next step, the testing of ppliction exmples for cyclic loding, is to simplify the lod collective for wind nd reduce the testing time y mens of endurnce strength theory. In order to descrie the generl ehvior of onded joints under cyclic loding, some pre-investigtions on smll scle specimens nd the fçde connection were crried out under constnt mplitudes. The stress rtio is chosen with vlue of.1, which mens vrying ut permnent tensile loding for the ondline. To prevent heting of the dhesive due to mechnicl lod, the tests were crried out with frequency of 5 Hz. If lod cycles re reched nd no dmge is detected, the vlue of the lod is ssigned within the ftigue strength. The results of these exmintions for polyurethne dhesive re shown in Fig. 9. Mximum lod [kn] Smll scle specimen: S k = 1.3 Specimen component: S k = 1.1 Adhesive sis: Polyurethn Sustrt: Steel Lod: Axil, sinusoidl Filure proility: 5 % R =.1 1/T s = 1.11 R =.1 1/T s = 1.38 Smll scle specimen Specimen component Cycles [-] S k Without frcture Ftigue strength [kn] Fig. 9. Comprison of test results of cyclic tests.

8 Yvonne Ciupck et l. / Procedi Engineering 172 ( 217 ) All specimens filed with cohesive filure of the ondline. The notch sensitivity (k) is clculted with vlue of for the utt joint tests nd of 6.48 for the fçde connection. The threshold of the lod, which the joint cn withstnd permnently (ftigue limit S k), is evluted with vlue of 1.3 kn for the smll scle specimen nd of 1.1 kn for the specimen component. 3. Conclusion nd Outlook The onding technology is more thn just n lterntive joining method for steel structures, which cn e shown y vrious pplictions nd reserch projects in different fields. Despite mny dvntges of onded joints the civil engineering nd especilly steel construction community is reluctnt in emrcing this innovtive technique. Often it is justified y douts out the durility nd lck of experience. Interpreting such douts s open questions nd chllenges cretes the possiility nd the potentil for exceptionl innovtions. The generl interest in developing stndrds s sis for nlysis nd design of dhesive joints in steel, is expected to rise with growing numer of functionl nd clculle pplictions. The future work for the presented ppliction exmples for fçde structures focuses on experimentl investigtions under vrile mplitudes nd the cretion of scientific sed guideline for the design of onded steel joints. For the introduction of lterntive innovtive onded steel joints, the effort is limited to the development of engineering-models, plnning nd construction design. Generl technicl pprovls or individul pprovls cn e chieved more esily, thus sustinly incresing the innovtive cpcity of smll nd medium-sized enterprises. Acknowledgements The IGF reserch project (IGF-No BG) of the Reserch Assocition for Steel Appliction (FOSTA), Sohnstrße 65, 4237 Düsseldorf, hs een funded y the AiF within the progrm for sponsorship y Industril Joint Reserch (IGF) of the Germn Federl Ministry of Economic Affirs nd Energy, sed on n enctment of the Germn Prliment. References [1] DIN EN , Structurl dhesives - Determintion of sher ehviour of structurl onds, Prt 2: Thick dherends sher test (ISO 113-2:21, modified), Germn version EN :24. [2] DIN EN 1587, Adhesives Determintion of tensile strength of utt joints (ISO 6922:1987 modified), Germn version EN 1587:29. [3] K. Dilger, H. Psternk et l., IGF Project No BG, Entwicklung eines Eurocode-sierten Bemessungskonzepts für Kleverindungen im Sthlu (in Anlehnung n DIN 199), Germny, 212. [4] J. Meinz, Kleen im Sthlu Betrchtungen zum Trg- und Verformungsverhlten und zum Nchweis gekleter Trpezprofilnschlüsse und verstärkter Hohlprofile in Pfosten-Riegel-Fssden, Disserttion, Brndenurgische Technische Universität Cottus, Germny, 21. [5] DIN EN 199, Eurocode : Bsis of structurl design; Germn version EN 199:22 + A1:25 + A1:25/AC:21, 21. [6] K. Dilger, H. Psternk et l., IGF Project No BG, Untersuchungen zum Trgverhlten und der Leensduer von Kleverindungen im Sthlu unter zyklischer Belstung, Germny, [7] DIN EN : Eurocode 1: Actions on structures Prt 1-5: Generl ctions Therml ctions; Germn version EN :23 + AC:29, 21. [8] DIN , Cldding for externl wlls, ventilted t rer Prt 1: Requirements, principles of testing, 21. [9] KIT, Institut für Meteorologie und Klimforschung (215):