STRENGTHENING OF STEEL AND HYBRID SHEAR WALLS

The 12th Interntionl Symposium on Fier Reinforced Polymers for Reinforced Concrete Structures (FRPRCS-12) & The 5th Asi-Pcific Conference on Fier Reinforced Polymers in Structures (APFIS-2015) Joint Conference, 14-16 Decemer 2015, Nnjing, Chin STRENGTHENING OF STEEL AND HYBRID SHEAR WALLS Ntlj Petkune 1 ; Ted Donchev 2, Hom Hdvini 3, Dvid Wertheim 4, Mukesh Limchiy 5 1 Kingston University London Emil: ntlj.petkune@gmil.com 2 Kingston University London Emil: T.Donchev@kingston.c.uk 3 Kingston University London Emil: H.Hdvini@kingston.c.uk 4 Kingston University London Emil: D.Wertheim@kingston.c.uk 5 Kingston University London Emil: M.Limchiy@kingston.c.uk Keywords: FRP, hyrid elements, composites, strengthening, sher wlls ABSTRACTS FRP mterils hve een intensively used for strengthening of reinforced concrete, steel, composite nd other structures for more thn 20 yers. Strengthening with FRP provides severl dvntges like light weight, high strength, resistnce to corrosion nd high verstility. This pper is going to discuss strengthening techniques for steel nd hyrid steel/frp sher wlls using CFRP nd GFRP. Two different types of specimens were developed. First type re three new specimens steel sher wll (SSW-1), hyrid cron sher wll (HCSW-1) nd hyrid glss sher wll (HGSW-1); second type re three strengthened specimens SSW-2, HCSW-2, HGSW-2 creted from first three specimens fter their testing till destruction. Six medium size sher wll specimens were tested under qusi-sttic seismic loding. For second type of sher wll specimens, strengthening of oundry elements of sher wlls ws done with ppliction of FRP fric nd lmintes; new infill pltes were used. Anlysis of the results ws done y compring the ehviour nd filure modes for new nd strengthened specimens fter initil testing. Specimens with proposed scheme for strengthening with FRP lmintes nd GFRP wrpping hd higher stiffness nd similr energy dissiption cpcity s new specimens. 1 INTRODUCTION Steel sher wlls (SSW) hve good lterl resisting properties in regions with high levels of seismic ctivity. Since 1970s they hve een populr in USA nd Jpn for construction of high-rise uildings providing significnt reduction in wll thickness, weight of the uilding nd s result reduction of foundtion lods [1]. Ltest reserch indictes opportunities for pplying thin wlled structures s well. When uildings re sujected to erthquke loding, severe dmges to sher wlls cn occur. It is importnt to use cost-effective techniques to recover initil strength, stiffness of the sher wll structure in order void demolition of the uilding or introduction of new dditionl elements. This pper will discuss the use of the composites to provide method for permnent

N. Petkune, T. Donchev, H. Hdvini, D. Wertheim, M. Limchiy strengthening of sher wlls fter erthquke dmges or cn provide post-strengthening solution, where structures require supporting higher lods for future design use. Experimentl studies were conducted to investigte ehviour of steel nd hyrid sher wlls under qusi-sttic loding nd their ehviour with strengthening techniques vi glss FRP (GFRP) nd cron FRP (CFRP) ppliction. 2 BACKGROUND Fire reinforced polymers (FRP) mterils hve een used in civil engineering re for few decdes for strengthening reinforced or pressed concrete structures, improving cpcity of ridges, dms nd tues. Most common fiers used for strengthening purposes re GFRP nd CFRP, s they hve numerous dvntges like high tensile strength, high strength-to-weight rtio, ese of the ppliction nd corrosion resistnce. Recently, FRP mterils hve een used for strengthening of steel structurl elements s well. They re used to enhnce seismic resistnce, ftigue loding, enhnces the serviceility nd ultimte strength of steel flexurl memers [2]. FRP cn e prticulrly eneficil in pplictions when it is importnt to void introducing residul stresses due to welding process. Teng et l. [3] discussed wide rnge of steel structures strengthened with FRP mterils nd highlighted the importnce of preprtion of the steel surfces nd properties of the dhesive nd their influence to the onding of oth mterils. Numerous studies were conducted on the ehviour of steel sher wlls; however limited studies re ville on the strengthening of the dmged sher wlls to recover their initil cpcity. Experimentl testing of dmged steel sher wlls with the use of GFRP i-directionl fric round columns nd infill plte ws proved s n effective temporry retrofitting solution. Lod cpcity of the strengthened specimen ws incresed in comprison to un-strengthened SSW, however significnt delmintion ws noticed s displcement ws incresed [4]. An innovtive lterl resisting system, hyrid sher wlls defined for the purpose of this project consisting of steel frmes nd steel infill pltes lminted with (FRP). Experimentl studies on the use of hyrid steel/gfrp sher wlls indicted higher stiffness, lrger energy dissiption properties nd more uniform tension field during loding thn steel sher wlls [5]. Nteghi et l. [6] tested steel sher wlls with infill pltes lminted with GFRP. Infill pltes lminted with GFRP significntly increse ultimte strength nd initil stiffness. Cumultive energy dissiption of the hyrid steel/gfrp sher wlls is lrger thn steel sher wlls. It lso hve to e noted tht direction of the fiers mtters s well, nd pplying lmintes in the direction of the tension field provides etter improvements. Hyrid sher wlls consisting of steel/cfrp mteril in comprison to steel sher wlls hve lrger energy dissiption, enhnced elstic stiffness nd sher cpcity [7]. Petkune et l. [8] investigted ehviour of steel GFRP nd CFRP sher wlls, this pper presents second phse of this project- strengthening of hyrid sher wlls. 3 METHODOLOGY 3.1 Description of specimen Specimens re scled model for sher wll design with height of 1025 mm nd width of 1090 mm (figure 1). Tested smples consist of steel frmes nd steel or hyrid infill pltes. Steel frme memers consist of two columns nd em ll of them mde from UB 127x76x27 sections. The frmes were designed t Kingston University nd produced y Cnnon Steels Ltd. Primry fish pltes were welded to steel frme. Figure 1 ) Dimensions of sher wll ) connection etween fish pltes nd infill plte

The 12th Interntionl Symposium on Fier Reinforced Polymers for Reinforced Concrete Structures (FRPRCS-12) & The 5th Asi-Pcific Conference on Fier Reinforced Polymers in Structures (APFIS-2015) Joint Conference, 14-16 Decemer 2015, Nnjing, Chin Two different types of specimens were tested. First type re three new specimens steel sher wll (SSW-1), hyrid cron sher wll (HCSW-1) nd hyrid glss sher wll (HGSW-1); second type re three strengthened specimens SSW-2, HCSW-2, HGSW-2 produced using the first type of specimens fter testing till destruction. For steel sher wll specimens, olted connection etween fish pltes nd infill pltes ws used. For ll hyrid specimens, in ddition to olted connection Epoxy Plus dhesive (Devcon) with sher strength of 20 MP ws used (figure 1). It ws used to compenste reltively wek connection etween FRP surfce nd steel due to low coefficient of friction. The specifiction of specimens is shown in tle 1. Tle 1 Description of specimens Nme of the specimen Lels Design configurtion of the infill plte Thicknesses of the infill plte, mm Steel Sher Wll SSW-1 Steel [S] 0.80 Strengthened Steel Sher Wll SSW-2 Steel [S] 1.40 Hyrid CFRP /Steel Sher Wll HCSW-1 [-45/+45/e/S/e/+45/-45] 1.70 Strengthened Hyrid CFRP HCSW-2 [-45/+45/e/S/e/+45/-45] 1.70 /Steel Sher Wll Hyrid GFRP/Steel Sher Wll HGSW-1 [-45/+45/e/S/e/+45/-45] 2.40 Strengthened Hyrid HGSW-2 [-45/+45/e/S/e/+45/-45] 2.40 GFRP/Steel Sher Wll Note: e- EF72 dhesive film The hyrid specimens re steel frmed with infill pltes which were prepred y lminting steel plte (0.8 mm) with two lyers of prepreg FRP mteril. The use of the prepreg FRP llowed the customiztion of the pltes in ccordnce to design configurtions in terms of the ngle inclintion nd numer of FRP lyers. Unidirectionl fiers were plced t ±45 o ngle of fiers, two lyers on oth sides of plte. For HCSW-1 nd HCSW-2, CFRP fric type MTM 28-1 series prepreg, with 127 GP tensile modulus (specified y mnufcturer Umeco Structurl mterils) ws lminted on ech side of the infill plte. For HGSW-1 nd HGSW-2, prepreg GFRP fric type Multipreg E722-02, with 71 GP tensile modulus (specified y mnufcturer (produced y Amer Composites) ws lminted to produce the hyrid infill plte. For preprtion of hyrid specimens, FRP lyers were ttched following mnufcturer s specifictions. Hyrid specimens were prepred y thoroughly clening steel plte with snd pper nd cetone. EF72 dhesive film (mnufctured y Amer Composites) with surfce weight of 100 g/m 2 ws plced etween steel plte nd FRP fric to crete etter ond for the infill pltes of ll four hyrid smples. Then FRP lyers were plced in ccordnce to design specifictions with orienttion of fiers indicted in tle 1. After tht, ech specimen ws plced inside vcuum g with pump hed nd plced inside oven. Oven/vcuum curing process ws done t rte of temperture increse of 3 o C per minute until 120 o C temperture nd minimum vcuum g pressure of 980 mr. Then constnt heting of 120 o C ws kept for 1 hour nd finlly the temperture decresed to 60 o C during cooling down cycle nd the smple ws left to cool vi externl ir fterwrds. 3.2 Preprtion of strengthened specimens (type 2) Second series of smples consist of three strengthened sher wll specimens: steel sher wll (SSW-2), hyrid CFRP/steel sher wll specimen (HCSW-2) nd hyrid GFRP/steel sher wll specimen (HGSW-2) fter testing under qusi-sttic loding until destruction. Specimens were strengthened vi ttchment of the CFRP lmintes on the frme, wrpping of the columns with GFRP fric, then removl nd replcement of infill plte. The infill pltes were removed nd replced with new ones. Dmged infill plte of steel sher wll specimen ws replced with new infill plte with thickness of 1.4 mm, which is thicker thn for type 1 smple due to strengthening considertions. Infill pltes in hyrid specimens were replced with new ones with the sme design specifictions s per type 1 specimens.

N. Petkune, T. Donchev, H. Hdvini, D. Wertheim, M. Limchiy The steel frmes of the specimens were strengthened with CFRP lmintes nd GFRP fric. Firstly, the pint ws removed with mechnicl wire rush to gurntee etter ond etween the steel nd the composites. Then the frme ws clened with white spirit to remove the dust nd oil dirt. Weer CFRP S&P CFK 150/2000 lmintes with thickness of 1.2 mm were ttched to the frme (figure 2) with moisture-tolernt structurl dhesive from Weer. Adhesive hs two components: isphenol epoxy resin nd polymine hrdener, which were mixed with proportion of 2.4:1 y mss. Adhesive ws pplied on the lmintes t pproximtely 3 mm thick lyer nd then the lmintes were ttched to the steel frme iming to cover the re of otined plstic hinges fter previous testing. After curing of the dhesive, the i-directionl woven glss fire wrpping (Weer) ws pplied round the whole surfce of the columns (figure 2). It ws cut ccording to the specifictions nd ttched to the frme using mixture of epoxy resin nd hrdener (2:1 y mss). 3.3 Testing set-up nd protocol Figure 2 Scheme for strengthening ) A-A nd B-B section of sher wll columns ) pln view of sher wll specimen Figure 3 shows test set-up. Test specimen ws fixed to rection frme vi olts nd clmps, with lterl supports preventing out-of-plne uckling of the specimen. Sher wll specimens were tested under qusi-sttic displcement controlled loding, which ws pplied vi loding system consisting of screw jck, electric motor, ger ox with cooling system nd inverter. Lod cell ws used for mesuring the lod nd liner vrile displcement trnsducers (LVDTs) were recording the displcements. Figure 3 ) test set-up for sher wll specimens ) qusi-sttic loding protocol (ATC-24)

The 12th Interntionl Symposium on Fier Reinforced Polymers for Reinforced Concrete Structures (FRPRCS-12) & The 5th Asi-Pcific Conference on Fier Reinforced Polymers in Structures (APFIS-2015) Joint Conference, 14-16 Decemer 2015, Nnjing, Chin Testing procedure ws followed in ccordnce to ATC-24 protocol from Applied Technicl Council (ATC-24, 1992). Figure 4 shows cyclic sinusoidl loding pplied for rnge of different mplitudes vrying from 0.4 mm to 35 mm displcement t slow rte. Initilly, three cycles of ech mplitude were pplied, nd then from 15 mm displcement numer of cycles ws decresed to two ccording to ATC-24 protocol. 4 RESULTS 4.1 Lod vs displcement Figure 5 shows comprison of the lod vs displcement vlues for SSW-1, SSW-2, HCSW-1, HCSW-2, HGSW-1 nd HGSW-2. Lod ws clculted tking the verge from the extreme vlues for ech of the cycles with the sme mplitude ove 5 mm. It cn e seen tht hyrid cron nd hyrid glss oth type 1 nd 2 specimens hve higher results thn steel sher wll specimens t every level of the displcement, indicting tht the use of the hyrid infill pltes improve lod cpcity significntly s expected [8]. The highest lod vlues were chieved y HGSW-1&2 specimens. Strengthened smples re compred with smples from type 1 to investigte the opportunity for effective strengthened of SW systems fter erthquke loding. Steel sher wll specimen (SSW-2) hs higher difference of 22% t 25 mm displcement, with lower difference of 12% t 30mm in comprison with SSW-1. The lod-displcement curves for HCSW1&2 nd HGSW1&2 re presented in figure 5. The ove discussed type of strengthening gives etter results thn originl smples (type 1) in the intervl 10 mm nd 30 mm for CFRP smples n in the intervl 5 mm nd 30 mm for GFRP smples. The increse of the cpcity fter strengthening in comprison with type 1 is etween 5% t 10 mm nd 16% t 30 mm for HCSW nd 2% t 5 mm nd 20% t 30 mm for HGSW. 4.1 Energy dissiption Figure 5 Lod vs Displcement Figure 6 shows energy dissiption grphs for SSW, HCSW nd HGSW for type 1 nd 2 clculted y estimting re within hysteretic curves, s shown in figure 6. Previous studies [8] showed tht energy dissiption for hyrid specimens of this type is higher thn for steel specimens. Energy dissiption increses significntly from 5 mm to 30 mm displcement.

N. Petkune, T. Donchev, H. Hdvini, D. Wertheim, M. Limchiy Figure 6 ) Hysteretic curves for hyrid specimens t 25 mm ) Energy Dissiption SSW-1&2, HCSW-1&2, HGSW-1&2 For hyrid specimens, energy dissiption for type 1 nd 2 were pproximtely the sme. Cummultive differences for energy dissiption is 6.5% for SSW, 2.2% for HCSW nd 1.7% for HGSW specimens. 6 CONCLUSIONS Steel sher wlls nd hyrid FRP sher wlls were tested fter strengthening with cron FRP lmintes nd glss FRP fric. The following conclusions cn e mde from the pper: Hyrid sher wlls of type 1 re hving higher lod ering cpcity, higher stiffness nd higher energy dissiption thn SSW system. Proposed wy of strengthening vi FRP stiffening of the frme nd replcement of infill plte is effective for ll 3 configurtions of smples. The increse of the cpcity is up to 16% for HCSW, 20% for HGSW nd 22% for SSW smples. The energy dissiption of strengthened smples is close to energy dissiption of the smples from type 1 with less thn 10% differences for ll specimens. REFERENCES [1] T.M. Roerts, Seismic resistnce of steel plte sher wlls, Engineering structures, 1995, 1:344-351. [2] S.Rizkll, M. Dwood, D. Schnerch, Development of cron fier reinforced polymer system for strengthening steel structures. Composites Prt A (Elsevier), 2008, 36: 388-397. [3] J.G. Teng, T. Yu, D. Fernndo, Strengthening of steel structures with fier-reinforced polymer composites, Journl of Construction Steel Reserch (Elsevier), 2012, 78:131-143. [4] N. Petkune, T. Donchev, D. Petkov, H. Hdvini, M. Limchiy, Y. Hussein, Opportunities for strengthening of dmged steel sher wlls. Proceedings of Conference on Civil Engineering Infrstructure Csed on Polymer Composites (CECOM), Krkow, Polnd. 2012. [5] A. Mleki, T. Donchev, H. Hdvini, M. Limchiy, Improving the seismic resistnce of structure using FRP/steel sher wlls. Proceedings of 6th interntionl Conference on Fier Reinforced Polymer (FRP) Composites in Civil Engineering (CICE2012), Rome, Itly, 2012. [6] F. Nteghi-Alhi, M. Khzei-Poul, Experimentl study of steel plte sher wlls with the infill pltes strengthened y GFRP lmintes. Journl of Construction Steel Reserch (Elsevier), 2012, 78:159-172. [7] F. Htmi, A. Ghmri, A. Rhi, Investigting the properties of steel sher wlls reinforced with Cron Fier Polymers (CFRP), Journl of Construction Steel Reserch, 2011, 70:36-42. [8] N. Petkune, T. Donchev, H. Hdvini, M. Limchiy, D. Wertheim, Investigtion of the ehviour of hyrid steel nd FRP sher wlls. Proceedings of 7th interntionl Conference on Fier Reinforced Polymer (FRP) Composites in Civil Engineering (CICE2014), Vncouver, Cnd. 2014.